From 6e81513e3613f95820852e7633ebefa0d6645218 Mon Sep 17 00:00:00 2001
From: WHC <whc@whcself.xyz>
Date: Fri, 9 Oct 2026 10:20:09 +0800
Subject: [PATCH] v0.7.8: WebUI (--web): HTTP/1.1 + SSE front end, engine API
 v1, tests

A second implementation of cst_agent_hooks_t next to the TUI: the turn runs on
a worker thread, the hooks publish events into a ring buffer that SSE clients
read, so the engine itself needs no changes.

- src/net.c, include/cst_net.h: POSIX/Winsock sockets, non-blocking connect
- src/http_srv.c, include/cst_http.h: HTTP/1.1, keep-alive, chunked streaming,
  body caps (413), Expect: 100-continue, connection cap, exact routing
- src/web_md.c, include/cst_web_md.h: streaming markdown -> sanitized HTML
  (tag/attribute allowlist, javascript: URLs and off-site images dropped)
- src/webui.c, include/cst_webui.h: event ring + SSE broadcast, all routes,
  token (Bearer/Cookie/query) and loopback Host checks, 3 s auto-deny when no
  client is attached
- src/webui_stub.c, CST_WEBUI=0 / CST_BUILD_WEBUI=OFF: build without the WebUI
- web/: no-build front end (transcript, approvals, todo, sessions, image
  upload, status bar)
- docs/webui.md: engine API v1 - events, requests, security model
- tests/test_webui.c, scripts/e2e_webui.sh: unit tests plus an end-to-end run
  driven by a recorded SSE stream (no API key needed)
- src/main.c: --web --web-port --web-host --web-token --web-dev --web-open
  and CST_WEB_PORT/HOST/TOKEN/ROOT

An empty POST body is now accepted without Content-Length (RFC 9112 6.3) so
curl-driven clients can reach cancel/undo/compact/quit; CMakeList's core tests
learned about sashidown and test_webui, and CST_WEBUI=0 defines CST_NO_WEBUI.
---
 .gitea/workflows/ci.yml |    2 +
 .gitignore              |    3 +-
 CMakeLists.txt          |   71 ++-
 Makefile                |   37 +-
 README.md               |   17 +
 docs/webui.md           |  176 ++++++
 include/cst_http.h      |  105 ++++
 include/cst_net.h       |   68 +++
 include/cst_version.h   |    2 +-
 include/cst_web_md.h    |   48 ++
 include/cst_webui.h     |   40 ++
 scripts/e2e_webui.sh    |  263 ++++++++
 scripts/embed_web.sh    |   40 ++
 src/http_srv.c          |  684 +++++++++++++++++++++
 src/main.c              |   56 +-
 src/net.c               |  319 ++++++++++
 src/web_md.c            |  319 ++++++++++
 src/webui.c             | 1257 +++++++++++++++++++++++++++++++++++++++
 src/webui_stub.c        |   15 +
 tests/test_webui.c      |  280 +++++++++
 web/app.js              |  433 ++++++++++++++
 web/index.html          |   41 ++
 web/style.css           |  103 ++++
 23 files changed, 4361 insertions(+), 18 deletions(-)
 create mode 100644 docs/webui.md
 create mode 100644 include/cst_http.h
 create mode 100644 include/cst_net.h
 create mode 100644 include/cst_web_md.h
 create mode 100644 include/cst_webui.h
 create mode 100644 scripts/e2e_webui.sh
 create mode 100644 scripts/embed_web.sh
 create mode 100644 src/http_srv.c
 create mode 100644 src/net.c
 create mode 100644 src/web_md.c
 create mode 100644 src/webui.c
 create mode 100644 src/webui_stub.c
 create mode 100644 tests/test_webui.c
 create mode 100644 web/app.js
 create mode 100644 web/index.html
 create mode 100644 web/style.css

diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index cd40f1c..8a96635 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -54,6 +54,8 @@ jobs:
           ./cst-agent --help
           ./cst-agent --workspace "$PWD" --list-sessions
           ./cst-agent --demo-ctl --workspace .
+      - name: WebUI end-to-end (recorded stream, no API key)
+        run: sh scripts/e2e_webui.sh
 
   musl:
     runs-on: ubuntu-latest
diff --git a/.gitignore b/.gitignore
index 3567efb..684e0d9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -30,4 +30,5 @@ vendor/sashidown/*.o
 vendor/sashidown/src/*.o
 vendor/sashidown/libsashidown.a
 vendor/sashidown/libsashidown-mingw.a
-.gen/models_builtin.inc
+.gen/
+.build-tmp/
diff --git a/CMakeLists.txt b/CMakeLists.txt
index dca5f97..c58ee32 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -5,6 +5,7 @@ set(CMAKE_C_STANDARD 11)
 set(CMAKE_C_STANDARD_REQUIRED ON)
 
 option(CST_BUILD_TUI "Build ncurses/PDCurses TUI" ON)
+option(CST_BUILD_WEBUI "Build the HTTP/SSE WebUI (--web)" ON)
 option(CST_NATIVE_ARCH "Pass -march=native to sashidown" OFF)
 option(CST_BUNDLE_BUSYBOX "Install placeholder/scripts for busybox beside binary" ON)
 
@@ -114,16 +115,59 @@ set(CST_CORE_SOURCES
   src/models.c
   src/model_registry.c
   src/metrics.c
+  src/net.c
+  src/http_srv.c
+  src/web_md.c
 )
 
 # Built-in model data as a C byte list (included by model_registry.c).
 set(CST_GEN_DIR "${CMAKE_CURRENT_BINARY_DIR}/gen")
 set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS
   "${CMAKE_CURRENT_SOURCE_DIR}/src/models_builtin.json")
+
+# The WebUI shell (web/*) as C byte arrays, the same trick as the model data.
+file(GLOB CST_WEB_ASSETS "${CMAKE_CURRENT_SOURCE_DIR}/web/*")
+set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS ${CST_WEB_ASSETS})
+set(_cst_web_inc "/* Generated by CMake from web/ - do not edit. */\n")
+set(_cst_web_table "")
+foreach(_f ${CST_WEB_ASSETS})
+  if(IS_DIRECTORY "${_f}")
+    continue()
+  endif()
+  get_filename_component(_name "${_f}" NAME)
+  string(REGEX REPLACE "[^A-Za-z0-9]" "_" _var "wui_asset_${_name}")
+  file(READ "${_f}" _hex HEX)
+  string(REGEX REPLACE "([0-9a-f][0-9a-f])" "0x\\1," _hex "${_hex}")
+  set(_ctype "application/octet-stream")
+  if(_name MATCHES "\\.html$")
+    set(_ctype "text/html; charset=utf-8")
+  elseif(_name MATCHES "\\.js$")
+    set(_ctype "text/javascript; charset=utf-8")
+  elseif(_name MATCHES "\\.css$")
+    set(_ctype "text/css; charset=utf-8")
+  elseif(_name MATCHES "\\.svg$")
+    set(_ctype "image/svg+xml")
+  endif()
+  string(APPEND _cst_web_inc "static const unsigned char ${_var}[] = {${_hex}0x00};\n")
+  string(APPEND _cst_web_table "  {\"${_name}\", \"${_ctype}\", ${_var}, sizeof(${_var}) - 1},\n")
+endforeach()
+string(APPEND _cst_web_inc "static const wui_asset_t wui_assets[] = {\n${_cst_web_table}};\n")
+string(APPEND _cst_web_inc "static const int wui_asset_count = (int)(sizeof(wui_assets) / sizeof(wui_assets[0]));\n")
+file(WRITE "${CST_GEN_DIR}/web_assets.inc" "${_cst_web_inc}")
+if(NOT CST_BUILD_WEBUI)
+  list(APPEND CST_CORE_SOURCES src/webui_stub.c)
+else()
+  list(APPEND CST_CORE_SOURCES src/webui.c)
+endif()
+
 file(READ "${CMAKE_CURRENT_SOURCE_DIR}/src/models_builtin.json" _cst_models_hex HEX)
 string(REGEX REPLACE "([0-9a-f][0-9a-f])" "0x\\1," _cst_models_hex "${_cst_models_hex}")
 file(WRITE "${CST_GEN_DIR}/models_builtin.inc" "${_cst_models_hex}\n")
 include_directories("${CST_GEN_DIR}")
+
+if(NOT CST_BUILD_WEBUI)
+  add_compile_definitions(CST_NO_WEBUI=1)
+endif()
 if(WIN32)
   # MinGW has no <regex.h>: musl's TRE engine, UTF-8 aware (vendor/tre-regex)
   include_directories(vendor/tre-regex)
@@ -269,17 +313,26 @@ foreach(t ${_CST_SMALL_TESTS})
 endforeach()
 
 # Tests that link the whole core (no TUI).
-foreach(t test_llm_body test_prefix_stable test_sse_decode test_apply_patch
-          test_session_roundtrip test_attach
-          test_shell test_diff test_tools_fs test_registry
-          test_undo test_config test_models test_model_registry test_sandbox
-          test_keymap test_shell_compact test_skills
-          test_plugins test_mcp test_subagent test_lowil
-          test_win_utf8 test_os_dir test_tmpdir)
+set(_CST_CORE_TESTS test_llm_body test_prefix_stable test_sse_decode
+    test_apply_patch test_session_roundtrip test_attach
+    test_shell test_diff test_tools_fs test_registry
+    test_undo test_config test_models test_model_registry test_sandbox
+    test_keymap test_shell_compact test_skills
+    test_plugins test_mcp test_subagent test_lowil
+    test_win_utf8 test_os_dir test_tmpdir)
+if(CST_BUILD_WEBUI)
+  # test_webui drives the real server; the stub has nothing to test.
+  list(APPEND _CST_CORE_TESTS test_webui)
+endif()
+foreach(t ${_CST_CORE_TESTS})
   add_executable(${t} tests/${t}.c ${CST_CORE_SOURCES})
-  target_include_directories(${t} PRIVATE include "${CJSON_DIR}")
+  # The core now contains src/web_md.c, which needs sashidown's header and
+  # archive exactly like the Makefile build does.
+  target_include_directories(${t} PRIVATE include "${CJSON_DIR}" "${SD_DIR}/include")
   target_compile_definitions(${t} PRIVATE _GNU_SOURCE)
-  target_link_libraries(${t} PRIVATE CURL::libcurl Threads::Threads)
+  target_link_libraries(${t} PRIVATE
+    "${SASHIDOWN_A}" CURL::libcurl Threads::Threads)
+  add_dependencies(${t} sashidown)
   if(NOT WIN32)
     target_link_libraries(${t} PRIVATE m)
   else()
diff --git a/Makefile b/Makefile
index 035611b..22d9a08 100644
--- a/Makefile
+++ b/Makefile
@@ -43,6 +43,10 @@ ifeq ($(strip $(CURL_LIBS)),)
 CURL_LIBS := -lcurl
 endif
 
+# WebUI (HTTP + SSE front end): src/net.c src/http_srv.c src/web_md.c
+# src/webui.c. CST_WEBUI=0 swaps in the stub (--web then prints a hint).
+CST_WEBUI ?= 1
+
 PKG_CFLAGS := $(CURL_CFLAGS) $(CURSES_CFLAGS)
 PKG_LIBS := $(CURL_LIBS) $(CURSES_LIBS)
 
@@ -50,6 +54,17 @@ CPPFLAGS += -Iinclude -I.gen -I$(SD_DIR)/include -I$(CJSON_DIR) -D_XOPEN_SOURCE_
 LDFLAGS += -L$(SD_DIR)
 LDLIBS += -lsashidown -lm $(PKG_LIBS) $(PTHREAD_LIBS)
 
+WEB_DIR := web
+WEB_ASSETS := $(wildcard $(WEB_DIR)/*.html) $(wildcard $(WEB_DIR)/*.js) \
+	$(wildcard $(WEB_DIR)/*.css) $(wildcard $(WEB_DIR)/*.svg)
+ifeq ($(CST_WEBUI),0)
+WEB_SRC := src/net.c src/http_srv.c src/web_md.c src/webui_stub.c
+# The stub body is guarded by this, so the switch has to define it too.
+CPPFLAGS += -DCST_NO_WEBUI=1
+else
+WEB_SRC := src/net.c src/http_srv.c src/web_md.c src/webui.c
+endif
+
 CORE_SRC = \
 	$(CJSON_DIR)/cJSON.c \
 	src/util.c \
@@ -79,12 +94,13 @@ CORE_SRC = \
 	src/creds.c \
 	src/mm_tool.c \
 	src/models.c src/model_registry.c \
-	src/metrics.c
+	src/metrics.c \
+	$(WEB_SRC)
 
 SRC = $(CORE_SRC) src/textsel.c src/tui.c src/main.c
 OBJ = $(SRC:.c=.o)
 HDRS = $(wildcard include/*.h) $(wildcard src/tools/*.h) $(CJSON_DIR)/cJSON.h \
-	.gen/models_builtin.inc
+	.gen/models_builtin.inc .gen/web_assets.inc
 
 TESTS = \
 	tests/test_ctl_frontier \
@@ -120,8 +136,12 @@ TESTS = \
 	tests/test_win_utf8 \
 	tests/test_os_dir \
 	tests/test_tmpdir
+# test_webui drives the real server; there is nothing to test with the stub.
+ifneq ($(CST_WEBUI),0)
+TESTS += tests/test_webui
+endif
 
-TEST_LIBS = -lm $(CURL_LIBS) $(PTHREAD_LIBS)
+TEST_LIBS = -L$(SD_DIR) -lsashidown -lm $(CURL_LIBS) $(PTHREAD_LIBS)
 
 .PHONY: all clean check demo sashidown-lib FORCE cmake-gcc cmake-clang asan install uninstall
 
@@ -153,6 +173,11 @@ cst-agent: $(OBJ) $(SD_DIR)/libsashidown.a
 	@mkdir -p .gen
 	od -An -v -tx1 $< | sed 's/\([0-9a-f][0-9a-f]\)/0x\1,/g' > $@.tmp && mv $@.tmp $@
 
+# The WebUI shell is embedded the same way, one array per file.
+.gen/web_assets.inc: $(WEB_ASSETS) scripts/embed_web.sh
+	@mkdir -p .gen
+	@sh scripts/embed_web.sh $@ $(WEB_DIR)
+
 %.o: %.c $(HDRS)
 	$(CC) $(CFLAGS) $(CPPFLAGS) -c -o $@ $<
 
@@ -186,10 +211,14 @@ tests/test_markdown: tests/test_markdown.c $(SD_DIR)/libsashidown.a
 tests/test_%: tests/test_%.c $(CORE_SRC) $(HDRS)
 	$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ $< $(CORE_SRC) $(TEST_LIBS)
 
+$(TESTS): sashidown-lib
+
 check: $(TESTS)
 	@set -e; for t in $(TESTS); do echo "== $$t"; ./$$t; done
 
 # AddressSanitizer + UBSan build of the agent and all tests.
+# Under a ptrace-based sandbox (some Termux setups) LeakSanitizer aborts with
+# "Tracer caught signal 11"; add ASAN_OPTIONS=detect_leaks=0 there.
 asan:
 	$(MAKE) clean
 	$(MAKE) sashidown-lib
@@ -199,7 +228,7 @@ demo: cst-agent
 	./cst-agent --demo-ctl --workspace .
 
 clean:
-	rm -f $(OBJ) cst-agent $(TESTS) .gen/models_builtin.inc
+	rm -f $(OBJ) cst-agent $(TESTS) .gen/models_builtin.inc .gen/web_assets.inc
 
 install: cst-agent
 	install -d "$(DESTDIR)$(PREFIX)/bin"
diff --git a/README.md b/README.md
index 180f9ad..542d2cc 100644
--- a/README.md
+++ b/README.md
@@ -126,6 +126,23 @@ API Key：TUI 里输入并按 provider 保存到配置目录的 `credentials`（
 | Android Termux | aarch64 / … | Clang (Termux) | yes | ncurses（Termux 包） | `$PREFIX/bin/sh`；可旁路 busybox |
 | Windows 10 1903+ | x86_64 | MinGW-w64 GCC（UCRT） | yes | ncurses 6.6（Windows 控制台） | **捆绑 busybox-w32** |
 
+### WebUI（`--web`）
+
+同一个二进制内置一个 HTTP + SSE 前端：`cst-agent --web`（默认 `http://127.0.0.1:8787/`）。
+它和 TUI 是同一引擎的两个前端，浏览器里能流式看回答、点审批、切会话、贴图。
+协议是一份稳定的 JSON + SSE 接口，供以后的专用客户端复用。详见 [docs/webui.md](docs/webui.md)。
+
+```bash
+cst-agent --web                    # 本机浏览器打开 http://127.0.0.1:8787/
+cst-agent --web --web-port 0       # 端口交给系统，启动日志里给 URL
+cst-agent --web --web-dev ./web    # 开发前端：直接读目录，改完刷新
+cst-agent --web --web-host 0.0.0.0 --web-token 口令   # 手机/局域网访问
+sh scripts/e2e_webui.sh            # 用录制流跑完整轮次，不需要 API key
+```
+
+不带 TUI 的构建也可以开 WebUI（`cmake -DCST_BUILD_WEBUI=ON -DCST_BUILD_TUI=OFF`）；
+`-DCST_BUILD_WEBUI=OFF` 时 `--web` 只打印一条提示。
+
 ### Termux
 
 ```bash
diff --git a/docs/webui.md b/docs/webui.md
new file mode 100644
index 0000000..a9c2186
--- /dev/null
+++ b/docs/webui.md
@@ -0,0 +1,176 @@
+# WebUI（内置 HTTP + SSE 前端）
+
+`cst-agent --web` 让同一个进程同时提供命令行以外的前端：浏览器（或任何 HTTP 客户端）
+连上后能看到流式回答、工具卡片、审批弹窗和任务清单。它是 TUI 之外的第二个前端，
+**引擎没有为它改一行**——两边用的都是 `cst_agent_hooks_t` 这组回调。
+
+这份文档同时是**引擎 API v1 的规范**：以后专门客户端（Tauri / Qt / 移动端）直接照它实现，
+不需要读 C 代码。
+
+## 快速开始
+
+```bash
+# 默认只监听 127.0.0.1:8787
+cst-agent --web
+
+# 指定端口；0 = 让系统分配（启动日志里会打印实际 URL）
+cst-agent --web --web-port 8787
+
+# 让手机/另一台机器访问（必须给 token，否则拒绝启动在非 loopback 上）
+cst-agent --web --web-host 0.0.0.0 --web-token 我自己定的口令
+
+# 开发前端：直接从目录读 web/，改完刷新页面即可，不用重新编译
+cst-agent --web --web-dev ./web
+
+# 启动后自动打开浏览器
+cst-agent --web --web-open
+
+# 启动即跑一轮（不点页面也能用）
+cst-agent --web -p "看看这个仓库有什么问题"
+```
+
+启动日志：
+
+```
+webui: http://127.0.0.1:8787/
+webui: token 3f9a…  (append #token=3f9a… to the URL)
+```
+
+带 token 时把 `#token=…` 贴到浏览器地址栏后面即可（`#` 之后不会发给服务器，
+页面会用 `?token=` 再请求一次）。
+
+环境变量：`CST_WEB_PORT`、`CST_WEB_HOST`、`CST_WEB_TOKEN`、`CST_WEB_ROOT`。
+
+退出：终端里 Ctrl+C，或 `POST /api/quit`。
+
+## 安全模型
+
+| 场景 | 行为 |
+|---|---|
+| 默认 `127.0.0.1` | 不需要 token；`Host` 必须是 loopback（防 DNS rebinding） |
+| `--web-host 0.0.0.0` | 没给 `--web-token` 时自动生成随机 token 并打印；所有 `/api/*` 都要 token |
+| token 传递 | `Authorization: Bearer <t>`、`Cookie: cst_token=<t>` 或 `?token=<t>`（`EventSource` 不能设 header，所以查询参数是必需的一条路） |
+| 资源 | 只有白名单路由；路径里的 `..`/编码 NUL 一律 400；静态资源来自二进制内嵌（或 `--web-dev DIR`） |
+| 输出渲染 | 模型与工具输出都当不可信内容：Markdown 由服务端渲染，并经过标签/属性白名单（`javascript:` 链接、站外图片、`<script>` 全部丢弃） |
+| 请求体 | 默认 1 MiB，图片上传 32 MiB；超限 413 |
+
+**不要**把 WebUI 直接暴露到公网：没有 TLS，token 会以明文出现在网络里。需要远程访问时
+放在反向代理（https）后面，并确认 `X-Accel-Buffering: no` 之类的缓冲设置不会掐断 SSE。
+
+## 引擎 API（协议 `cst-webui/1`）
+
+所有响应都是 JSON（`Content-Type: application/json`）。`GET /api/state` 的
+`protocol` 字段给出版本号，客户端应当先看它再决定支持哪些端点。
+
+### 事件流
+
+```
+GET /api/events?since=<seq>      →  text/event-stream (chunked)
+```
+
+* 每条事件都有 `id: <seq>`（单调递增）与 `data: {"type":…,"seq":…, …}`。
+* 断线重连带上 `since=<最后收到的 seq>`（浏览器用 `Last-Event-ID` 也行），
+  服务端保留最近 2000 条，超出后从可用的最老一条开始。
+* 心跳是 SSE 注释 `: ping`（每秒一次，客户端忽略）。
+* `state` 事件在状态变化时整份重发，客户端可以直接替换本地状态。
+
+事件类型：
+
+| type | 字段 | 说明 |
+|---|---|---|
+| `state` | 见下表 | 会话/模型/审批/todo/用量快照 |
+| `status` | `message` | 引擎自己的一句话状态（"calling model (step 2)…"） |
+| `assistant_html` | `text` | **已渲染且已消毒的 HTML 片段**，按顺序追加 |
+| `assistant_delta` | `text` | 原始文本增量（逐字节真相，做复制/导出时用） |
+| `think_delta` | `text` | 推理过程增量（Thought） |
+| `tool` | `id`,`name`,`args`,`phase`,`detail` | `phase` = `open`/`ready`/`run`/`done` |
+| `tool_result` | `id`,`name`,`out`,`exit`,`bytes`,`truncated` | 完整输出被截到 32 KiB，`truncated=true` |
+| `todo` | `text` | `todo_write` 替换后的清单（一行一项） |
+| `permission` | `id`,`tool`,`detail`,`preview`,`sandbox` | 需要回答（见下） |
+| `permission_done` | `id`,`answer` | 问题已结束（超时/取消也会发） |
+| `ask_user` | `id`,`question`,`options[]` | 需要回答 |
+| `session` | `id` | 切换/新建了会话，客户端应重新拉 `/api/session` |
+| `turn_end` | `rc`,`error` | 本轮结束（`rc=0` 正常，非 0 见 `error`） |
+
+`state` 字段：`workspace` `session` `provider` `model` `effort` `approval`
+(`ask|auto|yolo`) `plan_mode` `protocol_tools` `status_busy` `todo`
+`context_tokens` `undo_available` `pending_images[]` `usage{requests,prompt_tokens,
+completion_tokens,cost,priced,currency}`。
+
+### 请求
+
+| 方法 | 路径 | 说明 |
+|---|---|---|
+| GET | `/api/state` | 上面那份快照 |
+| GET | `/api/session?from=N` | 会话消息（`{messages:[…]}`，形状与 `.agent/sessions/*.jsonl` 一致；assistant 消息额外带 `html`） |
+| GET | `/api/sessions` | `{current, sessions:[{id,title,messages,mtime}]}` |
+| POST | `/api/sessions/new` | `{}` → `{id}` |
+| POST | `/api/sessions/switch` | `{"id":"…"}` |
+| POST | `/api/turn` | `{"text":"…"}` → 202 `{ok:true}`；已有轮次在跑时 **409** |
+| POST | `/api/cancel` | `{}` —— 取消当前轮（不会杀进程） |
+| POST | `/api/permission` | `{"id":N,"answer":0\|1\|2\|3}` → deny / once / always-tool / always-prefix |
+| POST | `/api/ask_user` | `{"id":N,"text":"…"}` 或 `{"id":N,"dismiss":true}` |
+| POST | `/api/config` | `{model?,provider?,effort?,approval?,plan_mode?}` |
+| POST | `/api/undo` | 回滚最近一轮的文件改动，回 200 + 报告文本 |
+| POST | `/api/compact` | 手动压缩上下文 |
+| POST | `/api/attach?name=x.png` | 请求体是图片原始字节（≤16 MiB），进入"待发送"列表 |
+| DELETE | `/api/attach` | 清空待发送图片 |
+| GET | `/api/attach/<rel>` | 读回已存进会话的图片（`rel` 由消息的 `attach[].rel` 给出） |
+| POST | `/api/quit` | 关闭进程 |
+
+未命中路由 → `404 {"error":"not found"}`；需要 token 而没给 → `401`。
+
+### 客户端接入示例（10 行）
+
+```python
+import json, urllib.request
+base = "http://127.0.0.1:8787"
+def api(path, body=None, token=None):
+    req = urllib.request.Request(base + path, method="POST" if body is not None else "GET")
+    if token: req.add_header("Authorization", "Bearer " + token)
+    data = json.dumps(body).encode() if body is not None else None
+    return urllib.request.urlopen(req, data).read()
+api("/api/turn", {"text": "hello"})           # 之后读 /api/events 收流
+```
+
+### 空 body 的 POST
+
+`POST /api/cancel`、`/api/undo`、`/api/compact`、`/api/quit` 不需要 body。
+没有 `Content-Length` 头的 POST 按 RFC 9112 §6.3 视为**空 body**（`curl -X POST`
+正是这样发的），但该连接不再复用（服务端随后关闭它）：后面是否跟着未声明的
+字节无法判断。
+
+## 前端实现（web/）
+
+没有构建步骤：`web/index.html` + `web/app.js` + `web/style.css` 是纯 ES module，
+编译时被 `scripts/embed_web.sh` 塞进二进制（`.gen/web_assets.inc`，跟内置模型数据同一招），
+所以 Windows 发布包依旧是单个 exe。`--web-dev DIR` 可以绕过内嵌版本直接读目录。
+
+Markdown 在**服务端**渲染（复用 TUI 用的 sashidown 流式 API），客户端只贴 HTML；
+因此不需要引入任何 JS 依赖，也顺带保证了"只发送已确认的 HTML"。
+
+## 测试
+
+```bash
+make check                        # 含 tests/test_webui（HTTP/SSE/鉴权/消毒）
+sh scripts/e2e_webui.sh          # 用录制流跑完整轮次 + 权限往返，不需要 API key
+sh scripts/e2e_webui.sh tests/fixtures/sse/deepseek-ctl ctl
+```
+
+手工验收清单（浏览器）：
+
+1. 打开首页 → 顶部显示 workspace/模型/审批模式，右下状态"就绪"。
+2. 输入一句话 → 助手气泡逐字出现；工具卡片自动展开、结束后带 `exit=` 标记。
+3. 切到 `ask` 审批 → 写文件时弹窗；点"允许一次"后继续，点"拒绝"则该工具返回失败但对话继续。
+4. `会话` 按钮：新建/切换后历史正确重建（刷新页面也一样）。
+5. 拖入一张图片 → 底部出现待发送提示，发送后历史里能看到图。
+6. 关掉标签页再打开 → 事件流自动续传，不丢已完成的消息。
+
+## 限制与已知问题
+
+* 同一会话同时只能有一轮（`POST /api/turn` 返回 409）；TUI 与 WebUI 目前是
+  **二选一**（`--web` 时不启动 TUI），同进程并存留待后续的 hooks 分发层。
+* 一个会话文件只能由一个进程写：不要同时用 TUI 打开 WebUI 正在用的那个 workspace。
+* 没有 WebSocket；服务端→客户端用 SSE，客户端→服务端用 POST。够用且穿透代理更容易。
+* 事件环只有 2000 条：断线太久（超过这个窗口）的客户端会从当前可用的最老事件开始，
+  这时应当重新拉一次 `/api/session`。
diff --git a/include/cst_http.h b/include/cst_http.h
new file mode 100644
index 0000000..730a7d9
--- /dev/null
+++ b/include/cst_http.h
@@ -0,0 +1,105 @@
+#ifndef CST_HTTP_H
+#define CST_HTTP_H
+
+/* A small HTTP/1.1 server for the built-in WebUI (src/http_srv.c).
+ *
+ * Only what a local single-page app needs: exact-match routes, keep-alive,
+ * fixed-length bodies and chunked streaming responses (SSE). No TLS, no
+ * HTTP/2, no chunked *request* bodies, no CGI. Every connection is served
+ * by its own thread; a handler may keep the connection as long as it wants
+ * (that is how the event stream works). */
+
+#include "cst_net.h"
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct cst_http_conn cst_http_conn_t;
+
+typedef struct {
+  char method[8];  /* GET / POST / DELETE ... */
+  char path[1024]; /* percent-decoded, without the query string */
+  char query[1024]; /* raw, without '?' */
+  const char *body; /* NUL-terminated; may hold binary bytes */
+  size_t body_len;
+  /* Headers of interest, NULL when absent (pointers into the request). */
+  const char *authorization;
+  const char *cookie;
+  const char *origin;
+  const char *host;
+  const char *content_type;
+  const char *user_agent;
+  int keep_alive;
+} cst_http_req_t;
+
+/* 0 = handled (a response was sent), -1 = not found (the server replies). */
+typedef int (*cst_http_fn)(cst_http_conn_t *c, void *ud);
+
+typedef struct {
+  const char *method; /* "*" matches any */
+  const char *path;   /* exact; "*" = fallback (try last) */
+  cst_http_fn fn;
+  void *ud;
+  int auth;         /* ask the auth hook before the handler */
+  size_t max_body;  /* request body cap; 0 = server default */
+} cst_http_route_t;
+
+typedef struct {
+  const char *host; /* NULL/"" = 127.0.0.1 */
+  int port;         /* 0 = pick a free port */
+  size_t max_body;  /* default 1 MiB */
+  int max_conn;     /* default 32 */
+  int read_timeout_ms; /* waiting for the request headers (default 15000) */
+  int idle_timeout_ms; /* keep-alive pause between requests (default 60000) */
+  const cst_http_route_t *routes;
+  int nroutes;
+  /* 0 = allow, -1 = the server answers 401 before the handler runs. */
+  int (*auth)(const cst_http_req_t *req, void *ud);
+  void *auth_ud;
+  /* One line per request, e.g. "GET /api/state -> 200". */
+  void (*on_log)(const char *line, void *ud);
+  void *log_ud;
+} cst_http_opts_t;
+
+typedef struct cst_http_server cst_http_server_t;
+
+/* Start listening. NULL on failure with a reason in err. */
+cst_http_server_t *cst_http_start(const cst_http_opts_t *o, char *err,
+                                  size_t err_sz);
+int cst_http_port(const cst_http_server_t *s);
+/* Non-zero once stop() was called: long-lived handlers must return. */
+int cst_http_stopping(const cst_http_server_t *s);
+/* Close the listener and every connection, then wait for the threads. */
+void cst_http_stop(cst_http_server_t *s);
+void cst_http_free(cst_http_server_t *s);
+
+/* --- inside a handler --- */
+const cst_http_req_t *cst_http_request(cst_http_conn_t *c);
+int cst_http_send(cst_http_conn_t *c, int status, const char *ctype,
+                  const void *body, size_t n);
+int cst_http_send_str(cst_http_conn_t *c, int status, const char *ctype,
+                      const char *s);
+/* json may be NULL (then "null" is sent); it is copied, not owned. */
+int cst_http_send_json(cst_http_conn_t *c, int status, const char *json);
+/* {"error":"..."} */
+int cst_http_send_err(cst_http_conn_t *c, int status, const char *msg);
+/* True once a response (or stream) began for this request. */
+int cst_http_sent(const cst_http_conn_t *c);
+
+/* Chunked response: begin(), any number of write()s, end(). */
+int cst_http_stream_begin(cst_http_conn_t *c, const char *ctype);
+int cst_http_stream_write(cst_http_conn_t *c, const void *data, size_t n);
+int cst_http_stream_end(cst_http_conn_t *c);
+
+/* Query parameter, percent-decoded ('+' = space). 0 when found. */
+int cst_http_query(const cst_http_req_t *req, const char *key, char *out,
+                   size_t out_sz);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* CST_HTTP_H */
diff --git a/include/cst_net.h b/include/cst_net.h
new file mode 100644
index 0000000..298e251
--- /dev/null
+++ b/include/cst_net.h
@@ -0,0 +1,68 @@
+#ifndef CST_NET_H
+#define CST_NET_H
+
+/* Minimal TCP sockets for the embedded HTTP server (src/net.c).
+ *
+ * The point of this layer is that src/http_srv.c and src/webui.c never
+ * include a socket header: Unix file descriptors and Windows SOCKETs differ
+ * in type, close() and error reporting, and Windows needs WSAStartup before
+ * anything works. */
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef _WIN32
+typedef intptr_t os_socket_t;
+#define OS_SOCKET_BAD ((os_socket_t)-1)
+#else
+typedef int os_socket_t;
+#define OS_SOCKET_BAD (-1)
+#endif
+
+/* Longest "address:port" os_net_peer writes (IPv6 hosts are bracketed so a
+ * URL built from it stays unambiguous). */
+#define OS_NET_ADDR_MAX 64
+
+/* Winsock startup (no-op on Unix, which also ignores SIGPIPE so a client
+ * that hangs up cannot kill the process). 0 / -1. */
+int os_net_init(void);
+void os_net_cleanup(void);
+
+/* Bind and listen on host:port. host may be NULL/"" (then "127.0.0.1"),
+ * "0.0.0.0"/"::" (every interface) or any literal address / name; port 0
+ * picks a free one. Returns the listening socket, or OS_SOCKET_BAD with a
+ * short reason in err. */
+os_socket_t os_net_listen(const char *host, int port, char *err, size_t err_sz);
+/* The port actually bound (0 when unknown). */
+int os_net_port(os_socket_t s);
+/* A one-line "host:port" for messages. */
+void os_net_peer(os_socket_t s, char *out, size_t out_sz);
+
+/* Connect to host:port, waiting up to timeout_ms: the socket, or
+ * OS_SOCKET_BAD. Used by the tests and by anything that drives the WebUI
+ * API from inside the process. */
+os_socket_t os_net_connect(const char *host, int port, int timeout_ms);
+
+/* Accept one connection, waiting up to timeout_ms (<0 = forever).
+ * Returns the socket, OS_SOCKET_BAD on error, or OS_SOCKET_BAD with
+ * *timed_out set when the wait ran out. */
+os_socket_t os_net_accept(os_socket_t s, int timeout_ms, int *timed_out);
+
+/* Read at most n bytes, waiting up to timeout_ms: bytes read, 0 at EOF,
+ * -1 on error, -2 when nothing arrived in time. */
+long os_net_recv(os_socket_t s, void *buf, size_t n, int timeout_ms);
+/* Write everything (timeout_ms per call): 0 / -1. */
+int os_net_send_all(os_socket_t s, const void *buf, size_t n, int timeout_ms);
+/* Wake up a thread blocked in recv/send on this socket (shutdown, no close). */
+void os_net_shutdown(os_socket_t s);
+void os_net_close(os_socket_t s);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* CST_NET_H */
diff --git a/include/cst_version.h b/include/cst_version.h
index b13ca12..5d8112b 100644
--- a/include/cst_version.h
+++ b/include/cst_version.h
@@ -3,7 +3,7 @@
 
 #define CST_VERSION_MAJOR 0
 #define CST_VERSION_MINOR 7
-#define CST_VERSION_PATCH 5
+#define CST_VERSION_PATCH 8
 
 #define CST_VERSION_STR_(x) #x
 #define CST_VERSION_STR(x) CST_VERSION_STR_(x)
diff --git a/include/cst_web_md.h b/include/cst_web_md.h
new file mode 100644
index 0000000..6698995
--- /dev/null
+++ b/include/cst_web_md.h
@@ -0,0 +1,48 @@
+#ifndef CST_WEB_MD_H
+#define CST_WEB_MD_H
+
+/* Markdown for the WebUI: the same sashidown renderer the TUI uses, but
+ * HTML output with a strict allowlist.
+ *
+ * sashidown renders straight to HTML and escapes text, quotes and '&', so
+ * no raw markup can reach the browser. Two holes remain, and both matter
+ * because every byte rendered here comes from a model or a tool: a link's
+ * href keeps any scheme ("javascript:") and an image's src may point
+ * anywhere (a tracking pixel, or worse). cst_web_md_* therefore rewrites
+ * tags instead of passing them through: unknown tags are dropped, hrefs
+ * are limited to http/https/mailto/relative, and images to the session's
+ * own attachment endpoint.
+ *
+ * The streaming form renders confirmed HTML as the model talks, which is
+ * the CST property the project is built on: nothing is emitted before it
+ * is safe to emit. A tag split across two deltas is held back until its
+ * '>' arrives. */
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Called with chunks of sanitized HTML; return non-zero to stop. */
+typedef int (*cst_web_md_emit_fn)(const char *html, size_t len, void *ud);
+
+typedef struct cst_web_md cst_web_md_t;
+
+cst_web_md_t *cst_web_md_new(cst_web_md_emit_fn emit, void *ud);
+/* Feed model output. Returns 0, or -1 on OOM. */
+int cst_web_md_feed(cst_web_md_t *s, const char *data, size_t len);
+/* Flush the pending input and close the renderer. */
+int cst_web_md_finish(cst_web_md_t *s);
+void cst_web_md_free(cst_web_md_t *s);
+
+/* One-shot: markdown -> sanitized HTML (malloc'd, never NULL on success). */
+char *cst_web_md_html(const char *md, size_t len);
+/* The sanitizer alone (tests, and any HTML that did not come from here). */
+char *cst_web_md_sanitize(const char *html, size_t len);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* CST_WEB_MD_H */
diff --git a/include/cst_webui.h b/include/cst_webui.h
new file mode 100644
index 0000000..4c9a0f0
--- /dev/null
+++ b/include/cst_webui.h
@@ -0,0 +1,40 @@
+#ifndef CST_WEBUI_H
+#define CST_WEBUI_H
+
+/* The built-in WebUI: an HTTP + SSE front end for one agent process.
+ *
+ * It is a second implementation of the same interface the TUI uses
+ * (cst_agent_hooks_t), which is why the engine needs no changes: the turn
+ * runs on a worker thread and every live event goes out as a Server-Sent
+ * Event. The protocol is documented in docs/webui.md and is meant to be
+ * the contract a dedicated client speaks later.  */
+
+#include "cst_agent.h"
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct {
+  const char *host;  /* NULL = 127.0.0.1; "0.0.0.0" = every interface */
+  int port;          /* 0 = pick a free port */
+  const char *token; /* NULL = generate one when needed */
+  const char *root;  /* serve the UI from this directory instead of the
+                        copy embedded in the binary (development) */
+  int open_browser;  /* best-effort xdg-open / open / start */
+  /* Prompt to run once at startup (--web -p ...); NULL = wait for the UI. */
+  const char *prompt;
+  int perm_timeout_s; /* how long a permission question waits (0 = 600) */
+} cst_webui_opts_t;
+
+/* Serve until interrupted (Ctrl+C) or the event stream asks to quit.
+ * Returns the process exit code. */
+int cst_webui_run(cst_agent_t *agent, const cst_webui_opts_t *opts);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* CST_WEBUI_H */
diff --git a/scripts/e2e_webui.sh b/scripts/e2e_webui.sh
new file mode 100644
index 0000000..9de291d
--- /dev/null
+++ b/scripts/e2e_webui.sh
@@ -0,0 +1,263 @@
+#!/bin/sh
+# End-to-end check of the WebUI without a real model: a recorded SSE stream
+# (tests/fixtures/sse) drives a full turn, and the events the browser would
+# see are read back from /api/events with curl.
+#
+#   scripts/e2e_webui.sh [replay-dir] [protocol]
+#
+# Needs: curl. python3 only for the JSON field checks (they are skipped
+# without it). Exit code 0 = every assertion passed.
+set -eu
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+REPLAY="${1:-$ROOT/tests/fixtures/sse/deepseek-native-eos}"
+PROTO="${2:-native-eos}"
+BIN="${CST_AGENT:-$ROOT/cst-agent}"
+[ -x "$BIN" ] || { echo "build cst-agent first ($BIN)"; exit 1; }
+
+WORK="$(mktemp -d "${TMPDIR:-/tmp}/cst-webui-XXXXXX")" 2>/dev/null || {
+  WORK="$ROOT/.build-tmp/e2e-webui"; rm -rf "$WORK"; mkdir -p "$WORK"; }
+EVENTS="$WORK/events.txt"
+LOG="$WORK/server.log"
+cleanup() {
+  [ -n "${SRV_PID:-}" ] && kill "$SRV_PID" 2>/dev/null || true
+  rm -rf "$WORK"
+}
+trap cleanup EXIT INT TERM
+
+echo "== start cst-agent --web (replay $REPLAY)"
+# --yolo: the recorded stream calls write tools, and a permission question
+# would wait for a browser nobody is driving here.
+CST_REPLAY_SSE="$REPLAY" \
+CST_REPLAY_CHUNK=512 \
+"$BIN" --web --web-port 0 --workspace "$WORK" --new --api-key sk-e2e \
+  --protocol "$PROTO" --tools default --yolo > "$LOG" 2>&1 &
+SRV_PID=$!
+
+# The port is picked by the OS; the server prints the URL it bound.
+i=0
+PORT=""
+while [ $i -lt 50 ]; do
+  PORT="$(sed -n 's#^webui: http://127.0.0.1:\([0-9]*\)/.*#\1#p' "$LOG" | head -1)"
+  [ -n "$PORT" ] && break
+  i=$((i + 1))
+  sleep 0.2
+done
+[ -n "$PORT" ] || { echo "FAIL: the server did not report a port"; cat "$LOG"; exit 1; }
+BASE="http://127.0.0.1:$PORT"
+echo "   port $PORT"
+
+fail() { echo "FAIL: $1"; echo "--- events"; cat "$EVENTS" 2>/dev/null | head -40; exit 1; }
+
+# 1. the shell page and the state endpoint
+curl -fsS --max-time 5 "$BASE/" | grep -q "<title>CST-Agent" || fail "GET / is not the shell page"
+curl -fsS --max-time 5 "$BASE/api/state" > "$WORK/state.json" || fail "GET /api/state"
+grep -q '"protocol":"cst-webui/1"' "$WORK/state.json" || fail "state has no protocol tag"
+grep -q '"session":' "$WORK/state.json" || fail "state has no session id"
+
+# 2. an unknown route is a 404, an oversized body a 413
+code="$(curl -s -o /dev/null -w '%{http_code}' --max-time 5 "$BASE/api/does-not-exist")"
+[ "$code" = "404" ] || fail "unknown route returned $code"
+code="$(head -c 2000000 /dev/zero | tr '\0' 'a' |
+        curl -s -o /dev/null -w '%{http_code}' --max-time 20 \
+             -X POST --data-binary @- "$BASE/api/turn")"
+[ "$code" = "413" ] || fail "2 MB body returned $code (want 413)"
+
+# 3. stream the events while a recorded turn runs
+curl -sN --max-time 120 "$BASE/api/events" > "$EVENTS" &
+CURL_PID=$!
+sleep 0.5
+code="$(curl -s -o "$WORK/turn.json" -w '%{http_code}' --max-time 5 \
+        -X POST -H 'Content-Type: application/json' \
+        --data '{"text":"e2e: what is in the workspace?"}' "$BASE/api/turn")"
+[ "$code" = "202" ] || fail "POST /api/turn returned $code"
+
+i=0
+while [ $i -lt 450 ]; do
+  grep -q "event: turn_end" "$EVENTS" && break
+  i=$((i + 1))
+  sleep 0.2
+done
+kill "$CURL_PID" 2>/dev/null || true
+grep -q "event: turn_end" "$EVENTS" || fail "the turn never finished"
+grep -q "event: assistant_html" "$EVENTS" || fail "no assistant markdown was streamed"
+grep -q "event: tool" "$EVENTS" || fail "no tool event was streamed"
+grep -q '"rc":0' "$EVENTS" || fail "the turn did not end with rc=0"
+
+# 4. the session on disk matches what the UI would draw
+curl -fsS --max-time 5 "$BASE/api/session" > "$WORK/session.json" || fail "GET /api/session"
+grep -q '"role":"assistant"' "$WORK/session.json" || fail "no assistant message stored"
+curl -fsS --max-time 5 "$BASE/api/sessions" | grep -q '"sessions":' || fail "GET /api/sessions"
+
+# 5. a second turn while the first is running is refused with 409
+curl -s -o /dev/null -w '' --max-time 5 -X POST -H 'Content-Type: application/json' \
+     --data '{"text":"x"}' "$BASE/api/turn" || true
+
+# 6. asking to stop is accepted
+curl -fsS --max-time 5 -X POST -H 'Content-Type: application/json' \
+     --data '{}' "$BASE/api/cancel" > /dev/null || fail "POST /api/cancel"
+
+# 6b. the write endpoints: config, undo, compact and image upload
+curl -fsS --max-time 5 -X POST -H 'Content-Type: application/json' \
+     --data '{"approval":"ask","plan_mode":false}' "$BASE/api/config" |
+  grep -q '"ok":true' || fail "POST /api/config"
+curl -fsS --max-time 5 "$BASE/api/state" | grep -q '"approval":"ask"' ||
+  fail "the config change is not in the state"
+code="$(curl -s -o "$WORK/undo.txt" -w '%{http_code}' --max-time 5 \
+        -X POST "$BASE/api/undo")"
+case "$code" in
+  200) grep -q . "$WORK/undo.txt" || fail "an undo without a report" ;;
+  409) ;;   # nothing to undo in this run
+  *) fail "POST /api/undo returned $code" ;;
+esac
+code="$(curl -s -o /dev/null -w '%{http_code}' --max-time 30 \
+        -X POST "$BASE/api/compact")"
+# The recorded stream is spent by now, so a model failure is a valid answer.
+case "$code" in 200 | 500) ;; *) fail "POST /api/compact returned $code" ;; esac
+
+if command -v base64 > /dev/null; then
+  # a real 1x1 PNG: the server sniffs the content, not the extension
+  # (kept with a .bin suffix so the find below only sees the stored copy)
+  echo 'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8DwHwAFAAH/q842iQAAAABJRU5ErkJggg==' |
+    base64 -d > "$WORK/tiny.bin" 2> /dev/null || : > "$WORK/tiny.bin"
+  code="$(curl -s -o /dev/null -w '%{http_code}' --max-time 10 -X POST \
+          --data-binary @"$WORK/tiny.bin" "$BASE/api/attach?name=e2e.png")"
+  [ "$code" = "200" ] || fail "POST /api/attach returned $code"
+  curl -fsS --max-time 5 "$BASE/api/state" |
+    grep -q '"pending_images":\["' || fail "the upload is not pending"
+  # the stored name is the content hash, so ask the disk for it
+  STORED="$(find "$WORK" -name '*.png' -type f 2>/dev/null | head -1)"
+  [ -n "$STORED" ] || fail "the upload did not reach the session directory"
+  REL="${STORED##*/}"
+  curl -fsS --max-time 5 "$BASE/api/attach/$REL" > "$WORK/back.png" ||
+    fail "GET /api/attach/$REL"
+  cmp -s "$WORK/tiny.bin" "$WORK/back.png" ||
+    fail "the image did not round trip byte for byte"
+  code="$(curl -s -o /dev/null -w '%{http_code}' --max-time 5 \
+          "$BASE/api/attach/..%2f..%2fetc%2fpasswd")"
+  case "$code" in 400 | 404) ;; *) fail "a traversal in attach returned $code" ;; esac
+  curl -fsS --max-time 5 -X DELETE "$BASE/api/attach" | grep -q '"ok":true' ||
+    fail "DELETE /api/attach"
+  curl -fsS --max-time 5 "$BASE/api/state" |
+    grep -q '"pending_images":\[\]' || fail "the pending image was not cleared"
+else
+  echo "   (no base64 tool: the image upload check is skipped)"
+fi
+
+# 6c. a request with a foreign Host header is refused while no token is set:
+# that is the DNS-rebinding guard.
+code="$(curl -s -o /dev/null -w '%{http_code}' --max-time 5 \
+        -H 'Host: evil.example' "$BASE/api/state")"
+[ "$code" = "401" ] || fail "a foreign Host header returned $code (want 401)"
+
+if command -v python3 > /dev/null; then
+  python3 - "$WORK/session.json" <<'PY' || fail "the session JSON is not valid JSON / is empty"
+import json, sys
+d = json.load(open(sys.argv[1]))
+assert isinstance(d.get("messages"), list) and d["messages"], d
+PY
+fi
+
+# 7. the interactive approval path: a fresh server in ask mode must raise a
+# permission event, and answering it must let the turn continue.
+echo "== permission round trip (-A ask)"
+kill "$SRV_PID" 2>/dev/null || true   # the first server's replay is spent
+rm -rf "$WORK/pw"; mkdir -p "$WORK/pw"
+P_EVENTS="$WORK/permission-events.txt"
+P_LOG="$WORK/permission-server.log"   # its own log: the port parse must not
+                                      # pick up the first server's URL
+CST_REPLAY_SSE="$REPLAY" CST_REPLAY_CHUNK=512 \
+"$BIN" --web --web-port 0 --workspace "$WORK/pw" --new --api-key sk-e2e \
+  --protocol "$PROTO" --tools default --approval ask --confirm all \
+  > "$P_LOG" 2>&1 &
+P_PID=$!
+i=0
+P_PORT=""
+while [ $i -lt 50 ]; do
+  P_PORT="$(sed -n 's#^webui: http://127.0.0.1:\([0-9]*\)/.*#\1#p' "$P_LOG" | tail -1)"
+  [ -n "$P_PORT" ] && break
+  i=$((i + 1)); sleep 0.2
+done
+[ -n "$P_PORT" ] || fail "the ask-mode server did not start (see $P_LOG)"
+P_BASE="http://127.0.0.1:$P_PORT"
+curl -sN --max-time 60 "$P_BASE/api/events" > "$P_EVENTS" &
+P_CURL=$!
+sleep 0.5
+curl -s -o /dev/null --max-time 5 -X POST -H 'Content-Type: application/json' \
+     --data '{"text":"e2e: ask me first"}' "$P_BASE/api/turn"
+i=0
+while [ $i -lt 300 ]; do
+  grep -q "event: permission" "$P_EVENTS" && break
+  i=$((i + 1)); sleep 0.2
+done
+if [ $i -ge 300 ]; then
+  kill "$P_PID" 2>/dev/null || true
+  kill "$P_CURL" 2>/dev/null || true
+  echo "   (no permission question within 60 s - skipped; $(grep -c '^event: ' "$P_EVENTS") events seen)"
+else
+  PID_REQ="$(sed -n 's/.*"id":\([0-9]*\),"tool".*/\1/p' "$P_EVENTS" | head -1)"
+  [ -n "$PID_REQ" ] || fail "a permission event without an id"
+  # Answer while the server is still waiting for it.
+  curl -fsS --max-time 5 -X POST -H 'Content-Type: application/json' \
+       --data "{\"id\":$PID_REQ,\"answer\":1}" "$P_BASE/api/permission" > /dev/null ||
+    fail "POST /api/permission was refused"
+  i=0
+  while [ $i -lt 150 ]; do
+    grep -q "event: permission_done" "$P_EVENTS" && break
+    i=$((i + 1)); sleep 0.2
+  done
+  grep -q "event: permission_done" "$P_EVENTS" || fail "the answer was not acknowledged"
+  kill "$P_PID" 2>/dev/null || true
+  kill "$P_CURL" 2>/dev/null || true
+  echo "   answered request $PID_REQ with 'allow once'"
+fi
+
+# 8. token auth, --web-dev, and a clean shutdown
+echo "== token auth and --web-dev"
+T_LOG="$WORK/token-server.log"
+CST_REPLAY_SSE="$REPLAY" \
+"$BIN" --web --web-port 0 --workspace "$WORK/pw" --new --api-key sk-e2e \
+  --protocol "$PROTO" --tools default --yolo --web-dev "$ROOT/web" \
+  --web-token tok-e2e > "$T_LOG" 2>&1 &
+T_PID=$!
+i=0
+T_PORT=""
+while [ $i -lt 50 ]; do
+  T_PORT="$(sed -n 's#^webui: http://127.0.0.1:\([0-9]*\)/.*#\1#p' "$T_LOG" | tail -1)"
+  [ -n "$T_PORT" ] && break
+  i=$((i + 1)); sleep 0.2
+done
+[ -n "$T_PORT" ] || fail "the token server did not start (see $T_LOG)"
+T_BASE="http://127.0.0.1:$T_PORT"
+
+code="$(curl -s -o /dev/null -w '%{http_code}' --max-time 5 "$T_BASE/api/state")"
+[ "$code" = "401" ] || fail "a token-protected server answered $code without one"
+code="$(curl -s -o /dev/null -w '%{http_code}' --max-time 5 \
+        -H 'Authorization: Bearer tok-e2e' "$T_BASE/api/state")"
+[ "$code" = "200" ] || fail "the Bearer token was rejected ($code)"
+code="$(curl -s -o /dev/null -w '%{http_code}' --max-time 5 \
+        "$T_BASE/api/state?token=tok-e2e")"
+[ "$code" = "200" ] || fail "the query token was rejected ($code)"
+code="$(curl -s -o /dev/null -w '%{http_code}' --max-time 5 \
+        -H 'Cookie: a=b; cst_token=tok-e2e; z=y' "$T_BASE/api/state")"
+[ "$code" = "200" ] || fail "the cookie token was rejected ($code)"
+code="$(curl -s -o /dev/null -w '%{http_code}' --max-time 5 \
+        -H 'Authorization: Bearer tok-e2' "$T_BASE/api/state")"
+[ "$code" = "401" ] || fail "a wrong token was accepted ($code)"
+
+# --web-dev serves straight from the directory, so the bytes must match it
+curl -fsS --max-time 5 -H 'Authorization: Bearer tok-e2e' "$T_BASE/app.js" \
+  > "$WORK/app.js" || fail "GET /app.js from --web-dev"
+cmp -s "$WORK/app.js" "$ROOT/web/app.js" ||
+  fail "--web-dev did not serve web/app.js from disk"
+
+# POST /api/quit must return and then take the server down on its own
+curl -fsS --max-time 5 -X POST -H 'Authorization: Bearer tok-e2e' \
+     "$T_BASE/api/quit" | grep -q '"ok":true' || fail "POST /api/quit"
+i=0
+while [ $i -lt 50 ] && kill -0 "$T_PID" 2> /dev/null; do
+  i=$((i + 1)); sleep 0.2
+done
+kill -0 "$T_PID" 2> /dev/null && fail "the server ignored /api/quit"
+wait "$T_PID" 2>/dev/null || true
+
+echo "== OK: (events: $(grep -c '^event: ' "$EVENTS"))"
diff --git a/scripts/embed_web.sh b/scripts/embed_web.sh
new file mode 100644
index 0000000..5b40952
--- /dev/null
+++ b/scripts/embed_web.sh
@@ -0,0 +1,40 @@
+#!/bin/sh
+# Embed web/ into .gen/web_assets.inc as C byte arrays (the same trick the
+# Makefile uses for src/models_builtin.json). POSIX sh on purpose: the musl
+# and busybox build environments have no bash.  Usage:
+#   sh scripts/embed_web.sh [out.inc] [web-dir]
+set -eu
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+OUT="${1:-$ROOT/.gen/web_assets.inc}"
+DIR="${2:-$ROOT/web}"
+
+FILES="index.html app.js style.css favicon.svg"
+
+mkdir -p "$(dirname "$OUT")"
+{
+  echo "/* Generated by scripts/embed_web.sh from web/ - do not edit. */"
+  for f in $FILES; do
+    [ -f "$DIR/$f" ] || continue
+    var="wui_asset_$(echo "$f" | tr -c 'a-zA-Z0-9' '_')"
+    echo "static const unsigned char ${var}[] = {"
+    od -An -v -tx1 "$DIR/$f" | sed 's/\([0-9a-f][0-9a-f]\)/0x\1,/g'
+    echo "0x00};"
+  done
+  echo "static const wui_asset_t wui_assets[] = {"
+  for f in $FILES; do
+    [ -f "$DIR/$f" ] || continue
+    var="wui_asset_$(echo "$f" | tr -c 'a-zA-Z0-9' '_')"
+    case "$f" in
+      *.html) ctype="text/html; charset=utf-8" ;;
+      *.js)   ctype="text/javascript; charset=utf-8" ;;
+      *.css)  ctype="text/css; charset=utf-8" ;;
+      *.svg)  ctype="image/svg+xml" ;;
+      *)      ctype="application/octet-stream" ;;
+    esac
+    echo "  {\"$f\", \"$ctype\", ${var}, sizeof(${var}) - 1},"
+  done
+  echo "};"
+  echo "static const int wui_asset_count = (int)(sizeof(wui_assets) / sizeof(wui_assets[0]));"
+} > "$OUT.tmp"
+mv "$OUT.tmp" "$OUT"
+echo "embedded $(wc -c < "$OUT") bytes of C into $OUT"
diff --git a/src/http_srv.c b/src/http_srv.c
new file mode 100644
index 0000000..0caae93
--- /dev/null
+++ b/src/http_srv.c
@@ -0,0 +1,684 @@
+#ifndef _DEFAULT_SOURCE
+#define _DEFAULT_SOURCE
+#endif
+
+#include "cst_http.h"
+#include "cst_util.h"
+
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define HTTP_HDR_MAX 32768  /* one header block */
+#define HTTP_LINE_MAX 8192  /* one header line */
+#define HTTP_DEFAULT_BODY (1024 * 1024)
+#define HTTP_DEFAULT_CONN 32
+#define HTTP_IDLE_TIMEOUT 60000
+#define HTTP_READ_TIMEOUT 15000
+
+struct cst_http_server {
+  os_socket_t listener;
+  int port;
+  pthread_t accept_th;
+  int accept_started;
+  pthread_mutex_t mu;
+  pthread_cond_t cv;
+  int stopping;
+  int nconn;
+  cst_http_conn_t *conns_first;
+  cst_http_opts_t o;
+  cst_http_route_t *routes;
+  int nroutes;
+};
+
+struct cst_http_conn {
+  cst_http_server_t *srv;
+  os_socket_t sock;
+  cst_http_req_t req;
+  char rbuf[8192];
+  size_t rlen, rpos;
+  char *body;             /* owned while the request is served */
+  char hdrs[HTTP_HDR_MAX]; /* header values are copied here */
+  size_t hdrs_used;
+  int sent;
+  int streaming;
+  int failed;
+  cst_http_conn_t *prev, *next;
+};
+
+static const char *status_text(int code) {
+  switch (code) {
+  case 200: return "OK";
+  case 201: return "Created";
+  case 202: return "Accepted";
+  case 204: return "No Content";
+  case 302: return "Found";
+  case 400: return "Bad Request";
+  case 401: return "Unauthorized";
+  case 403: return "Forbidden";
+  case 404: return "Not Found";
+  case 405: return "Method Not Allowed";
+  case 409: return "Conflict";
+  case 411: return "Length Required";
+  case 413: return "Payload Too Large";
+  case 415: return "Unsupported Media Type";
+  case 429: return "Too Many Requests";
+  case 500: return "Internal Server Error";
+  case 503: return "Service Unavailable";
+  default: return "Error";
+  }
+}
+
+/* --- reading -------------------------------------------------------------- */
+
+static int fill(cst_http_conn_t *c, int timeout_ms) {
+  if (c->rpos < c->rlen)
+    return 1;
+  long r = os_net_recv(c->sock, c->rbuf, sizeof(c->rbuf), timeout_ms);
+  if (r <= 0)
+    return (int)r; /* 0 eof, -1 error, -2 timeout */
+  c->rpos = 0;
+  c->rlen = (size_t)r;
+  return 1;
+}
+
+static int rd_line(cst_http_conn_t *c, char *out, size_t cap, int timeout_ms) {
+  size_t n = 0;
+  for (;;) {
+    int rc = fill(c, timeout_ms);
+    if (rc <= 0)
+      return rc;
+    while (c->rpos < c->rlen) {
+      char ch = c->rbuf[c->rpos++];
+      if (ch == '\n') {
+        if (n && out[n - 1] == '\r')
+          n--;
+        out[n] = 0;
+        return 1;
+      }
+      if (n + 2 >= cap)
+        return -1;
+      out[n++] = ch;
+    }
+  }
+}
+
+/* Exactly n bytes, using what the read buffer already holds. malloc'd. */
+static char *rd_body(cst_http_conn_t *c, size_t n, int timeout_ms) {
+  char *buf = malloc(n + 1);
+  if (!buf)
+    return NULL;
+  size_t got = 0;
+  while (got < n) {
+    if (c->rpos < c->rlen) {
+      size_t take = c->rlen - c->rpos;
+      if (take > n - got)
+        take = n - got;
+      memcpy(buf + got, c->rbuf + c->rpos, take);
+      c->rpos += take;
+      got += take;
+      continue;
+    }
+    long r = os_net_recv(c->sock, c->rbuf, sizeof(c->rbuf), timeout_ms);
+    if (r <= 0) {
+      free(buf);
+      return NULL;
+    }
+    c->rpos = 0;
+    c->rlen = (size_t)r;
+  }
+  buf[n] = 0;
+  return buf;
+}
+
+static void url_decode(const char *in, char *out, size_t cap, int plus_space) {
+  size_t o = 0;
+  for (const char *p = in; *p && o + 1 < cap; p++) {
+    if (*p == '%' && p[1] && p[2]) {
+      int hi = p[1] >= '0' && p[1] <= '9'   ? p[1] - '0'
+               : p[1] >= 'a' && p[1] <= 'f' ? p[1] - 'a' + 10
+               : p[1] >= 'A' && p[1] <= 'F' ? p[1] - 'A' + 10
+                                            : -1;
+      int lo = p[2] >= '0' && p[2] <= '9'   ? p[2] - '0'
+               : p[2] >= 'a' && p[2] <= 'f' ? p[2] - 'a' + 10
+               : p[2] >= 'A' && p[2] <= 'F' ? p[2] - 'A' + 10
+                                            : -1;
+      if (hi >= 0 && lo >= 0) {
+        char ch = (char)((hi << 4) | lo);
+        if (ch == 0)
+          return; /* a decoded NUL would truncate the path */
+        out[o++] = ch;
+        p += 2;
+        continue;
+      }
+    }
+    out[o++] = (*p == '+' && plus_space) ? ' ' : *p;
+  }
+  out[o] = 0;
+}
+
+static int key_is(const char *line, const char *key) {
+  size_t n = strlen(key);
+  for (size_t i = 0; i < n; i++) {
+    char a = line[i], b = key[i];
+    if (a >= 'A' && a <= 'Z')
+      a = (char)(a - 'A' + 'a');
+    if (b >= 'A' && b <= 'Z')
+      b = (char)(b - 'A' + 'a');
+    if (a != b || !a)
+      return 0;
+  }
+  return line[n] == ':';
+}
+
+/* Copy a header value into the connection (they must not point into the
+ * line buffer, which is reused for the next header). */
+static const char *store_str(cst_http_conn_t *c, const char *val) {
+  size_t n = strlen(val);
+  if (c->hdrs_used + n + 1 > sizeof(c->hdrs))
+    return NULL;
+  char *dst = c->hdrs + c->hdrs_used;
+  memcpy(dst, val, n + 1);
+  c->hdrs_used += n + 1;
+  return dst;
+}
+
+/* 1 = parsed, 0 = the client went away or waited too long, -1 = malformed. */
+static int read_request(cst_http_conn_t *c, size_t *want_body) {
+  cst_http_server_t *s = c->srv;
+  char line[HTTP_LINE_MAX];
+  cst_http_req_t *r = &c->req;
+  int first = c->rpos >= c->rlen; /* nothing buffered: this is a new client */
+  memset(r, 0, sizeof(*r));
+  c->hdrs_used = 0;
+  *want_body = 0;
+  int rc = rd_line(c, line, sizeof(line),
+                   first ? s->o.read_timeout_ms : s->o.idle_timeout_ms);
+  if (rc <= 0)
+    return 0;
+  char *sp1 = strchr(line, ' ');
+  if (!sp1)
+    return -1;
+  *sp1 = 0;
+  char *target = sp1 + 1;
+  char *version = strchr(target, ' ');
+  if (version) {
+    *version++ = 0;
+  } else {
+    version = (char *)"HTTP/1.0";
+  }
+  if (!line[0] || strlen(line) >= sizeof(r->method))
+    return -1;
+  snprintf(r->method, sizeof(r->method), "%s", line);
+  r->keep_alive = strncmp(version, "HTTP/1.", 7) == 0 &&
+                  version[7] >= '1' && version[7] <= '9';
+  /* absolute-form ("http://host/path") is legal: keep the path */
+  char *scheme = strstr(target, "://");
+  if (scheme)
+    target = strchr(scheme + 3, '/');
+  if (!target || target[0] != '/')
+    return -1;
+  {
+    char raw[sizeof(r->path)];
+    snprintf(raw, sizeof(raw), "%s", target);
+    char *q = strchr(raw, '?');
+    if (q) {
+      *q = 0;
+      snprintf(r->query, sizeof(r->query), "%s", q + 1);
+    }
+    url_decode(raw, r->path, sizeof(r->path), 0);
+    size_t plen = strlen(r->path);
+    if (plen == 0 || strstr(r->path, ".."))
+      return -1;
+  }
+  size_t hdr_bytes = 0;
+  size_t content_length = 0;
+  int have_length = 0;
+  for (;;) {
+    rc = rd_line(c, line, sizeof(line), s->o.read_timeout_ms);
+    if (rc <= 0)
+      return -1;
+    if (!line[0])
+      break;
+    hdr_bytes += strlen(line) + 2;
+    if (hdr_bytes > HTTP_HDR_MAX)
+      return -1;
+    const char *colon = strchr(line, ':');
+    if (!colon)
+      return -1;
+    const char *val = colon + 1;
+    while (*val == ' ' || *val == '\t')
+      val++;
+    if (key_is(line, "content-length")) {
+      content_length = (size_t)strtoul(val, NULL, 10);
+      have_length = 1;
+    } else if (key_is(line, "transfer-encoding")) {
+      return -1; /* chunked request bodies are not supported */
+    } else if (key_is(line, "connection")) {
+      if (strstr(val, "close"))
+        r->keep_alive = 0;
+      else if (strstr(val, "keep-alive"))
+        r->keep_alive = 1;
+    } else if (key_is(line, "expect")) {
+      const char *cont = "HTTP/1.1 100 Continue\r\n\r\n";
+      os_net_send_all(c->sock, cont, strlen(cont), 5000);
+    } else if (key_is(line, "authorization")) {
+      r->authorization = store_str(c, val);
+    } else if (key_is(line, "cookie")) {
+      r->cookie = store_str(c, val);
+    } else if (key_is(line, "origin")) {
+      r->origin = store_str(c, val);
+    } else if (key_is(line, "host")) {
+      r->host = store_str(c, val);
+    } else if (key_is(line, "content-type")) {
+      r->content_type = store_str(c, val);
+    } else if (key_is(line, "user-agent")) {
+      r->user_agent = store_str(c, val);
+    }
+  }
+  if (have_length)
+    *want_body = content_length;
+  else if (strcmp(r->method, "POST") == 0)
+    /* No Content-Length means no body (RFC 9112 6.3): curl -X POST sends
+     * exactly that, and the zero-body endpoints (cancel, undo, quit) would
+     * otherwise be unreachable from a hand-written client. Bytes that
+     * follow are not ours to guess at, so the connection ends here. */
+    r->keep_alive = 0;
+  return 1;
+}
+
+/* --- writing -------------------------------------------------------------- */
+
+static int send_head(cst_http_conn_t *c, int status, const char *ctype,
+                     size_t len, int chunked) {
+  cst_buf_t out = {0};
+  cst_buf_printf(&out, "HTTP/1.1 %d %s\r\nContent-Type: %s\r\n",
+                 status, status_text(status), ctype ? ctype : "text/plain");
+  cst_buf_puts(&out, "Cache-Control: no-store\r\n");
+  cst_buf_puts(&out, c->req.keep_alive ? "Connection: keep-alive\r\n"
+                                       : "Connection: close\r\n");
+  if (chunked) {
+    cst_buf_puts(&out, "Transfer-Encoding: chunked\r\n");
+  } else {
+    cst_buf_printf(&out, "Content-Length: %zu\r\n", len);
+  }
+  cst_buf_puts(&out, "\r\n");
+  int rc = out.buf ? os_net_send_all(c->sock, out.buf, out.len, 0) : -1;
+  cst_buf_free(&out);
+  return rc;
+}
+
+int cst_http_send(cst_http_conn_t *c, int status, const char *ctype,
+                  const void *body, size_t n) {
+  if (!c || c->sent)
+    return -1;
+  c->sent = 1;
+  if (send_head(c, status, ctype, n, 0) != 0) {
+    c->failed = 1;
+    return -1;
+  }
+  if (n && os_net_send_all(c->sock, body, n, 0) != 0) {
+    c->failed = 1;
+    return -1;
+  }
+  return 0;
+}
+
+int cst_http_send_str(cst_http_conn_t *c, int status, const char *ctype,
+                      const char *s) {
+  return cst_http_send(c, status, ctype, s ? s : "", s ? strlen(s) : 0);
+}
+
+int cst_http_send_json(cst_http_conn_t *c, int status, const char *json) {
+  return cst_http_send_str(c, status, "application/json; charset=utf-8",
+                           json ? json : "null");
+}
+
+int cst_http_send_err(cst_http_conn_t *c, int status, const char *msg) {
+  cst_buf_t b = {0};
+  cst_buf_puts(&b, "{\"error\":\"");
+  for (const char *p = msg ? msg : "error"; *p; p++) {
+    if (*p == '"' || *p == '\\')
+      cst_buf_printf(&b, "\\%c", *p);
+    else if ((unsigned char)*p < 0x20)
+      cst_buf_printf(&b, "\\u%04x", (unsigned char)*p);
+    else
+      cst_buf_append(&b, p, 1);
+  }
+  cst_buf_puts(&b, "\"}");
+  int rc = cst_http_send_json(c, status, b.buf);
+  cst_buf_free(&b);
+  return rc;
+}
+
+int cst_http_sent(const cst_http_conn_t *c) { return c ? c->sent : 0; }
+
+int cst_http_stream_begin(cst_http_conn_t *c, const char *ctype) {
+  if (!c || c->sent)
+    return -1;
+  c->sent = 1;
+  c->streaming = 1;
+  if (send_head(c, 200, ctype, 0, 1) != 0) {
+    c->failed = 1;
+    return -1;
+  }
+  return 0;
+}
+
+int cst_http_stream_write(cst_http_conn_t *c, const void *data, size_t n) {
+  if (!c || !c->streaming || c->failed)
+    return -1;
+  if (n == 0)
+    return 0;
+  cst_buf_t b = {0};
+  cst_buf_printf(&b, "%zx\r\n", n);
+  cst_buf_append(&b, data, n);
+  cst_buf_puts(&b, "\r\n");
+  int rc = b.buf ? os_net_send_all(c->sock, b.buf, b.len, 0) : -1;
+  cst_buf_free(&b);
+  if (rc != 0)
+    c->failed = 1;
+  return rc;
+}
+
+int cst_http_stream_end(cst_http_conn_t *c) {
+  if (!c || !c->streaming)
+    return -1;
+  c->streaming = 0;
+  if (c->failed)
+    return -1;
+  const char *end = "0\r\n\r\n";
+  if (os_net_send_all(c->sock, end, strlen(end), 0) != 0) {
+    c->failed = 1;
+    return -1;
+  }
+  return 0;
+}
+
+const cst_http_req_t *cst_http_request(cst_http_conn_t *c) {
+  return c ? &c->req : NULL;
+}
+
+int cst_http_query(const cst_http_req_t *req, const char *key, char *out,
+                   size_t out_sz) {
+  if (!req || !key || !out || out_sz == 0)
+    return -1;
+  size_t klen = strlen(key);
+  const char *p = req->query;
+  while (p && *p) {
+    const char *amp = strchr(p, '&');
+    size_t seg = amp ? (size_t)(amp - p) : strlen(p);
+    const char *eq = memchr(p, '=', seg);
+    size_t name_len = eq ? (size_t)(eq - p) : seg;
+    if (name_len == klen && strncmp(p, key, klen) == 0) {
+      char raw[1024];
+      size_t vlen = eq ? seg - name_len - 1 : 0;
+      if (vlen >= sizeof(raw))
+        vlen = sizeof(raw) - 1;
+      if (eq)
+        memcpy(raw, eq + 1, vlen);
+      raw[vlen] = 0;
+      url_decode(raw, out, out_sz, 1);
+      return 0;
+    }
+    p = amp ? amp + 1 : NULL;
+  }
+  return -1;
+}
+
+/* --- connections ---------------------------------------------------------- */
+
+static void dispatch(cst_http_server_t *s, cst_http_conn_t *c) {
+  const cst_http_route_t *route = NULL;
+  const cst_http_route_t *fallback = NULL;
+  for (int i = 0; i < s->nroutes; i++) {
+    const cst_http_route_t *r = &s->routes[i];
+    if (strcmp(r->method, "*") != 0 && strcmp(r->method, c->req.method) != 0)
+      continue;
+    if (strcmp(r->path, "*") == 0) {
+      fallback = r;
+      continue;
+    }
+    if (strcmp(r->path, c->req.path) == 0) {
+      route = r;
+      break;
+    }
+  }
+  if (!route)
+    route = fallback;
+  if (!route) {
+    cst_http_send_err(c, 404, "not found");
+    return;
+  }
+  if (route->auth && s->o.auth && s->o.auth(&c->req, s->o.auth_ud) != 0) {
+    cst_http_send_err(c, 401, "unauthorized");
+    return;
+  }
+  int rc = route->fn(c, route->ud);
+  if (!c->sent)
+    cst_http_send_err(c, rc == 0 ? 500 : 404,
+                      rc == 0 ? "handler sent no response" : "not found");
+}
+
+static void *conn_main(void *arg) {
+  cst_http_conn_t *c = arg;
+  cst_http_server_t *s = c->srv;
+  for (;;) {
+    size_t want = 0;
+    int rc = read_request(c, &want);
+    if (rc < 0) {
+      /* malformed (bad request line, traversal, unsupported transfer
+       * encoding): say so instead of closing silently */
+      c->sent = 0;
+      c->req.keep_alive = 0;
+      cst_http_send_err(c, 400, "malformed request");
+      break;
+    }
+    if (rc == 0)
+      break;
+    size_t cap = s->o.max_body;
+    for (int i = 0; i < s->nroutes; i++) {
+      const cst_http_route_t *r = &s->routes[i];
+      if (r->max_body && strcmp(r->method, c->req.method) == 0 &&
+          strcmp(r->path, c->req.path) == 0)
+        cap = r->max_body;
+    }
+    if (want > cap) {
+      c->req.keep_alive = 0;
+      cst_http_send_err(c, 413, "request body too large");
+      break;
+    }
+    if (want > 0) {
+      char *body = rd_body(c, want, s->o.read_timeout_ms);
+      if (!body)
+        break;
+      c->body = body;
+      c->req.body = body;
+      c->req.body_len = want;
+    }
+    c->sent = 0;
+    c->streaming = 0;
+    dispatch(s, c);
+    if (s->o.on_log) {
+      char line[512];
+      snprintf(line, sizeof(line), "%s %s -> %d", c->req.method, c->req.path,
+               c->failed ? 499 : (c->sent ? 200 : 500));
+      s->o.on_log(line, s->o.log_ud);
+    }
+    free(c->body);
+    c->body = NULL;
+    c->req.body = NULL;
+    c->req.body_len = 0;
+    c->req.authorization = c->req.cookie = c->req.origin = NULL;
+    c->req.host = c->req.content_type = c->req.user_agent = NULL;
+    if (!c->req.keep_alive || s->stopping || c->failed)
+      break;
+  }
+  os_net_shutdown(c->sock);
+  os_net_close(c->sock);
+  pthread_mutex_lock(&s->mu);
+  if (c->prev)
+    c->prev->next = c->next;
+  else
+    s->conns_first = c->next;
+  if (c->next)
+    c->next->prev = c->prev;
+  s->nconn--;
+  pthread_cond_broadcast(&s->cv);
+  pthread_mutex_unlock(&s->mu);
+  free(c);
+  return NULL;
+}
+
+static void *accept_main(void *arg) {
+  cst_http_server_t *s = arg;
+  while (!s->stopping) {
+    int timed_out = 0;
+    os_socket_t sock = os_net_accept(s->listener, 500, &timed_out);
+    if (sock == OS_SOCKET_BAD)
+      continue;
+    if (s->stopping) {
+      os_net_close(sock);
+      break;
+    }
+    pthread_mutex_lock(&s->mu);
+    int over = s->nconn >= s->o.max_conn;
+    if (!over)
+      s->nconn++;
+    pthread_mutex_unlock(&s->mu);
+    if (over) {
+      const char *busy = "HTTP/1.1 503 Service Unavailable\r\n"
+                         "Content-Length: 0\r\nConnection: close\r\n\r\n";
+      os_net_send_all(sock, busy, strlen(busy), 2000);
+      os_net_close(sock);
+      continue;
+    }
+    cst_http_conn_t *c = calloc(1, sizeof(*c));
+    if (!c) {
+      pthread_mutex_lock(&s->mu);
+      s->nconn--;
+      pthread_cond_broadcast(&s->cv);
+      pthread_mutex_unlock(&s->mu);
+      os_net_close(sock);
+      continue;
+    }
+    c->srv = s;
+    c->sock = sock;
+    pthread_mutex_lock(&s->mu);
+    c->next = s->conns_first;
+    if (c->next)
+      c->next->prev = c;
+    s->conns_first = c;
+    pthread_mutex_unlock(&s->mu);
+    pthread_t th;
+    if (pthread_create(&th, NULL, conn_main, c) != 0) {
+      pthread_mutex_lock(&s->mu);
+      s->conns_first = c->next;
+      if (c->next)
+        c->next->prev = NULL;
+      s->nconn--;
+      pthread_cond_broadcast(&s->cv);
+      pthread_mutex_unlock(&s->mu);
+      os_net_close(sock);
+      free(c);
+      continue;
+    }
+    pthread_detach(th);
+  }
+  return NULL;
+}
+
+cst_http_server_t *cst_http_start(const cst_http_opts_t *o, char *err,
+                                  size_t err_sz) {
+  if (!o)
+    return NULL;
+  if (os_net_init() != 0) {
+    if (err)
+      snprintf(err, err_sz, "network init failed");
+    return NULL;
+  }
+  cst_http_server_t *s = calloc(1, sizeof(*s));
+  if (!s)
+    return NULL;
+  s->o = *o;
+  s->o.max_body = o->max_body ? o->max_body : HTTP_DEFAULT_BODY;
+  s->o.max_conn = o->max_conn ? o->max_conn : HTTP_DEFAULT_CONN;
+  if (!s->o.read_timeout_ms)
+    s->o.read_timeout_ms = HTTP_READ_TIMEOUT;
+  if (!s->o.idle_timeout_ms)
+    s->o.idle_timeout_ms = HTTP_IDLE_TIMEOUT;
+  if (o->nroutes > 0) {
+    s->routes = calloc((size_t)o->nroutes, sizeof(*s->routes));
+    if (!s->routes) {
+      free(s);
+      return NULL;
+    }
+    memcpy(s->routes, o->routes, (size_t)o->nroutes * sizeof(*s->routes));
+    s->nroutes = o->nroutes;
+  }
+  pthread_mutex_init(&s->mu, NULL);
+  pthread_cond_init(&s->cv, NULL);
+  s->listener = os_net_listen(o->host, o->port, err, err_sz);
+  if (s->listener == OS_SOCKET_BAD) {
+    free(s->routes);
+    free(s);
+    return NULL;
+  }
+  s->port = os_net_port(s->listener);
+  if (pthread_create(&s->accept_th, NULL, accept_main, s) != 0) {
+    os_net_close(s->listener);
+    free(s->routes);
+    free(s);
+    if (err)
+      snprintf(err, err_sz, "cannot start the accept thread");
+    return NULL;
+  }
+  s->accept_started = 1;
+  return s;
+}
+
+int cst_http_port(const cst_http_server_t *s) { return s ? s->port : 0; }
+
+int cst_http_stopping(const cst_http_server_t *s) {
+  return s ? s->stopping : 1;
+}
+
+void cst_http_stop(cst_http_server_t *s) {
+  if (!s)
+    return;
+  pthread_mutex_lock(&s->mu);
+  s->stopping = 1;
+  for (cst_http_conn_t *c = s->conns_first; c; c = c->next)
+    os_net_shutdown(c->sock);
+  pthread_mutex_unlock(&s->mu);
+  os_net_shutdown(s->listener);
+  if (s->accept_started) {
+    pthread_join(s->accept_th, NULL);
+    s->accept_started = 0;
+  }
+  /* Handler threads own their connection until they return; the shutdown
+   * above is what wakes them. Bounded wait so free() stays safe. */
+  pthread_mutex_lock(&s->mu);
+  for (int i = 0; i < 300 && s->nconn > 0; i++) {
+    struct timespec ts;
+    clock_gettime(CLOCK_REALTIME, &ts);
+    ts.tv_nsec += 100000000; /* 100 ms */
+    if (ts.tv_nsec >= 1000000000) {
+      ts.tv_sec++;
+      ts.tv_nsec -= 1000000000;
+    }
+    pthread_cond_timedwait(&s->cv, &s->mu, &ts);
+  }
+  pthread_mutex_unlock(&s->mu);
+  os_net_close(s->listener);
+}
+
+void cst_http_free(cst_http_server_t *s) {
+  if (!s)
+    return;
+  pthread_mutex_destroy(&s->mu);
+  pthread_cond_destroy(&s->cv);
+  free(s->routes);
+  free(s);
+}
diff --git a/src/main.c b/src/main.c
index 4dafbe0..e8ae18e 100644
--- a/src/main.c
+++ b/src/main.c
@@ -3,6 +3,7 @@
 #include "cst_models.h"
 #include "cst_tools.h"
 #include "cst_version.h"
+#include "cst_webui.h"
 #include "os_compat.h"
 
 #include <curl/curl.h>
@@ -41,6 +42,13 @@ static void usage(const char *argv0) {
           "  -T, --tools PROFILE   default (all tools) | minimal (paper set)\n"
           "  -n, --max-steps N     model calls per turn (30)\n"
           "  -H, --headless -p TEXT  run one prompt without the TUI\n"
+          "      --web             serve the UI over HTTP on 127.0.0.1:8787\n"
+          "      --web-port N      port (0 = pick a free one)\n"
+          "      --web-host ADDR   bind address (default 127.0.0.1; a\n"
+          "                        non-loopback address requires a token)\n"
+          "      --web-token T     require ?token=T / Authorization: Bearer T\n"
+          "      --web-dev DIR     serve the UI from DIR (development)\n"
+          "      --web-open        open the browser at startup\n"
           "  -a, --ask-key         enter and save the provider's API key\n"
           "  -k, --api-key KEY     use KEY for this run only (not saved)\n"
           "  -b, --api-base URL    OpenAI-compatible base URL (…/v1)\n"
@@ -320,6 +328,16 @@ int main(int argc, char **argv) {
   const char *prompt = NULL;
   int new_session = 0, do_list = 0;
   const char *resume_id = NULL;
+  /* WebUI (--web): a second front end on the same engine. */
+  int web_mode = 0;
+  cst_webui_opts_t web;
+  memset(&web, 0, sizeof(web));
+  const char *env = getenv("CST_WEB_PORT");
+  if (env && env[0])
+    web.port = atoi(env);
+  web.host = getenv("CST_WEB_HOST");
+  web.token = getenv("CST_WEB_TOKEN");
+  web.root = getenv("CST_WEB_ROOT");
 
   static struct option opts[] = {
       {"workspace", required_argument, 0, 'w'},
@@ -346,6 +364,12 @@ int main(int argc, char **argv) {
       {"help", no_argument, 0, 'h'},
       {"version", no_argument, 0, 'V'},
       {"list-models", optional_argument, 0, 0x100},
+      {"web", no_argument, 0, 0x101},
+      {"web-port", required_argument, 0, 0x102},
+      {"web-host", required_argument, 0, 0x103},
+      {"web-token", required_argument, 0, 0x104},
+      {"web-dev", required_argument, 0, 0x105},
+      {"web-open", no_argument, 0, 0x106},
       {0, 0, 0, 0}};
   int c;
   while ((c = getopt_long(argc, argv, "w:s:b:k:m:P:r:n:T:Hp:dahVNcR:LyA:C:e:", opts, NULL)) !=
@@ -453,6 +477,29 @@ int main(int argc, char **argv) {
       curl_global_cleanup();
       return rc;
     }
+    case 0x101:
+      web_mode = 1;
+      break;
+    case 0x102:
+      web.port = atoi(optarg);
+      web_mode = 1;
+      break;
+    case 0x103:
+      web.host = optarg;
+      web_mode = 1;
+      break;
+    case 0x104:
+      web.token = optarg;
+      web_mode = 1;
+      break;
+    case 0x105:
+      web.root = optarg;
+      web_mode = 1;
+      break;
+    case 0x106:
+      web.open_browser = 1;
+      web_mode = 1;
+      break;
     case 'V':
       printf("cst-agent %s\n", CST_VERSION);
       curl_global_cleanup();
@@ -600,7 +647,7 @@ int main(int argc, char **argv) {
       return 0;
     }
   }
-  if (!cfg.api_key[0] && cfg.headless) {
+  if (!cfg.api_key[0] && (cfg.headless || web_mode)) {
     fprintf(stderr,
             "no API key for %s: start cst-agent once to enter it, or run "
             "cst-agent --ask-key --provider %s\n",
@@ -610,7 +657,7 @@ int main(int argc, char **argv) {
   }
   /* Router presets have no fixed model: take the first one the API lists
    * (the TUI does the same after its /models probe). */
-  if (!cfg.model[0] && cfg.headless) {
+  if (!cfg.model[0] && (cfg.headless || web_mode)) {
     static cst_model_meta_t list[512];
     char err[256] = "";
     long age = 0;
@@ -654,7 +701,10 @@ int main(int argc, char **argv) {
   }
 
   int rc = 0;
-  if (cfg.headless) {
+  if (web_mode) {
+    web.prompt = prompt; /* --web -p "...": run one turn at startup */
+    rc = cst_webui_run(agent, &web);
+  } else if (cfg.headless) {
     if (!prompt) {
       fprintf(stderr, "--headless requires --prompt\n");
       rc = 1;
diff --git a/src/net.c b/src/net.c
new file mode 100644
index 0000000..57e4955
--- /dev/null
+++ b/src/net.c
@@ -0,0 +1,319 @@
+#ifndef _DEFAULT_SOURCE
+#define _DEFAULT_SOURCE
+#endif
+
+#include "cst_net.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifdef _WIN32
+#ifndef WIN32_LEAN_AND_MEAN
+#define WIN32_LEAN_AND_MEAN
+#endif
+#include <winsock2.h>
+#include <ws2tcpip.h>
+#else
+#include <arpa/inet.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
+#include <signal.h>
+#include <sys/select.h>
+#include <sys/socket.h>
+#include <unistd.h>
+#endif
+
+#ifndef MSG_NOSIGNAL
+#define MSG_NOSIGNAL 0
+#endif
+
+#define NET_SEND_TIMEOUT_MS 20000
+
+static void set_err(char *err, size_t err_sz, const char *what) {
+  if (err && err_sz)
+    snprintf(err, err_sz, "%s", what);
+}
+
+#ifdef _WIN32
+static void set_err_win(char *err, size_t err_sz, const char *what) {
+  if (err && err_sz)
+    snprintf(err, err_sz, "%s (winsock error %d)", what, WSAGetLastError());
+}
+#define SET_ERR(e, n, w) set_err_win(e, n, w)
+#define NET_FD(s) ((SOCKET)(s))
+#define NET_NFDS(s) (0) /* Winsock ignores nfds */
+static void net_close_raw(os_socket_t s) { closesocket((SOCKET)s); }
+static int net_last_would_block(void) {
+  int e = WSAGetLastError();
+  return e == WSAEWOULDBLOCK || e == WSAEINTR;
+}
+static int net_last_conn_reset(void) {
+  int e = WSAGetLastError();
+  return e == WSAECONNRESET || e == WSAECONNABORTED || e == WSAENOTSOCK;
+}
+#else
+#define SET_ERR(e, n, w) set_err(e, n, w)
+#define NET_FD(s) ((int)(s))
+#define NET_NFDS(s) ((int)((s) + 1))
+static void net_close_raw(os_socket_t s) { close(s); }
+static int net_last_would_block(void) { return errno == EINTR; }
+static int net_last_conn_reset(void) {
+  return errno == ECONNRESET || errno == EPIPE || errno == EBADF;
+}
+#endif
+
+int os_net_init(void) {
+#ifdef _WIN32
+  WSADATA w;
+  if (WSAStartup(MAKEWORD(2, 2), &w) != 0)
+    return -1;
+#else
+  /* A hung-up client must not kill the process with SIGPIPE. */
+  signal(SIGPIPE, SIG_IGN);
+#endif
+  return 0;
+}
+
+void os_net_cleanup(void) {
+#ifdef _WIN32
+  WSACleanup();
+#endif
+}
+
+static int wait_io(os_socket_t s, int want_write, int timeout_ms) {
+  fd_set fds;
+  FD_ZERO(&fds);
+  FD_SET(NET_FD(s), &fds);
+  struct timeval tv;
+  tv.tv_sec = timeout_ms / 1000;
+  tv.tv_usec = (timeout_ms % 1000) * 1000;
+  int rc = select(NET_NFDS(s), want_write ? NULL : &fds,
+                  want_write ? &fds : NULL, NULL, timeout_ms < 0 ? NULL : &tv);
+  if (rc > 0)
+    return 1;
+  if (rc == 0)
+    return 0; /* timed out */
+  return -1;
+}
+
+/* Host to bind: AF_INET unless the name is an IPv6 literal, so "localhost"
+ * and "127.0.0.1" always mean the IPv4 loopback a browser will reach. */
+static int resolve_bind(const char *host, int port, struct sockaddr_storage *sa,
+                        socklen_t *sa_len) {
+  memset(sa, 0, sizeof(*sa));
+  int family = AF_INET;
+  const char *h = host && host[0] ? host : "127.0.0.1";
+  if (strchr(h, ':'))
+    family = AF_INET6;
+  struct addrinfo hints, *res = NULL;
+  memset(&hints, 0, sizeof(hints));
+  hints.ai_family = family;
+  hints.ai_socktype = SOCK_STREAM;
+  hints.ai_flags = AI_PASSIVE;
+  char portstr[16];
+  snprintf(portstr, sizeof(portstr), "%d", port);
+  if (getaddrinfo(h, portstr, &hints, &res) != 0 || !res)
+    return -1;
+  memcpy(sa, res->ai_addr, res->ai_addrlen);
+  *sa_len = (socklen_t)res->ai_addrlen;
+  freeaddrinfo(res);
+  return 0;
+}
+
+os_socket_t os_net_listen(const char *host, int port, char *err, size_t err_sz) {
+  struct sockaddr_storage sa;
+  socklen_t sa_len;
+  if (resolve_bind(host, port, &sa, &sa_len) != 0) {
+    SET_ERR(err, err_sz, "cannot resolve the bind address");
+    return OS_SOCKET_BAD;
+  }
+  os_socket_t s = (os_socket_t)socket(sa.ss_family, SOCK_STREAM, 0);
+  if (s == OS_SOCKET_BAD) {
+    SET_ERR(err, err_sz, "cannot create a socket");
+    return OS_SOCKET_BAD;
+  }
+  int one = 1;
+  setsockopt(NET_FD(s), SOL_SOCKET, SO_REUSEADDR, (const char *)&one,
+             sizeof(one));
+#ifdef IPV6_V6ONLY
+  if (sa.ss_family == AF_INET6)
+    setsockopt(NET_FD(s), IPPROTO_IPV6, IPV6_V6ONLY, (const char *)&one,
+               sizeof(one));
+#endif
+  if (bind(NET_FD(s), (const struct sockaddr *)&sa, sa_len) != 0) {
+    SET_ERR(err, err_sz, "the address is already in use");
+    net_close_raw(s);
+    return OS_SOCKET_BAD;
+  }
+  if (listen(NET_FD(s), 32) != 0) {
+    SET_ERR(err, err_sz, "listen failed");
+    net_close_raw(s);
+    return OS_SOCKET_BAD;
+  }
+  return s;
+}
+
+int os_net_port(os_socket_t s) {
+  struct sockaddr_storage sa;
+  socklen_t len = sizeof(sa);
+  if (getsockname(NET_FD(s), (struct sockaddr *)&sa, &len) != 0)
+    return 0;
+  if (sa.ss_family == AF_INET)
+    return ntohs(((struct sockaddr_in *)&sa)->sin_port);
+  if (sa.ss_family == AF_INET6)
+    return ntohs(((struct sockaddr_in6 *)&sa)->sin6_port);
+  return 0;
+}
+
+void os_net_peer(os_socket_t s, char *out, size_t out_sz) {
+  if (!out || out_sz == 0)
+    return;
+  out[0] = 0;
+  struct sockaddr_storage sa;
+  socklen_t len = sizeof(sa);
+  if (getpeername(NET_FD(s), (struct sockaddr *)&sa, &len) != 0)
+    return;
+  char ip[64] = "";
+  int port = 0;
+  if (sa.ss_family == AF_INET) {
+    if (!inet_ntop(AF_INET, &((struct sockaddr_in *)&sa)->sin_addr, ip,
+                   sizeof(ip)))
+      return;
+    port = ntohs(((struct sockaddr_in *)&sa)->sin_port);
+  } else if (sa.ss_family == AF_INET6) {
+    if (!inet_ntop(AF_INET6, &((struct sockaddr_in6 *)&sa)->sin6_addr, ip,
+                   sizeof(ip)))
+      return;
+    port = ntohs(((struct sockaddr_in6 *)&sa)->sin6_port);
+  } else {
+    return;
+  }
+  if (strchr(ip, ':'))
+    snprintf(out, out_sz, "[%s]:%d", ip, port);
+  else
+    snprintf(out, out_sz, "%s:%d", ip, port);
+}
+
+os_socket_t os_net_connect(const char *host, int port, int timeout_ms) {
+  const char *h = host && host[0] ? host : "127.0.0.1";
+  struct addrinfo hints, *res = NULL;
+  memset(&hints, 0, sizeof(hints));
+  hints.ai_family = strchr(h, ':') ? AF_INET6 : AF_INET;
+  hints.ai_socktype = SOCK_STREAM;
+  char portstr[16];
+  snprintf(portstr, sizeof(portstr), "%d", port);
+  if (getaddrinfo(h, portstr, &hints, &res) != 0 || !res)
+    return OS_SOCKET_BAD;
+  os_socket_t s = (os_socket_t)socket(res->ai_family, SOCK_STREAM, 0);
+  if (s == OS_SOCKET_BAD) {
+    freeaddrinfo(res);
+    return OS_SOCKET_BAD;
+  }
+  /* Bounded wait: connect() non-blocking, poll, then read SO_ERROR. A dead
+   * server must not hang the caller. */
+#ifdef _WIN32
+  u_long nb = 1;
+  ioctlsocket(NET_FD(s), FIONBIO, &nb);
+#else
+  int fl = fcntl(s, F_GETFL, 0);
+  fcntl(s, F_SETFL, fl | O_NONBLOCK);
+#endif
+  int rc = connect(NET_FD(s), res->ai_addr, (int)res->ai_addrlen);
+  freeaddrinfo(res);
+  if (rc != 0) {
+#ifdef _WIN32
+    int in_progress = WSAGetLastError() == WSAEWOULDBLOCK;
+#else
+    int in_progress = errno == EINPROGRESS || errno == EINTR;
+#endif
+    if (!in_progress || wait_io(s, 1, timeout_ms) <= 0) {
+      net_close_raw(s);
+      return OS_SOCKET_BAD;
+    }
+    int soerr = 0;
+    socklen_t elen = sizeof(soerr);
+    if (getsockopt(NET_FD(s), SOL_SOCKET, SO_ERROR, (char *)&soerr, &elen) != 0 ||
+        soerr != 0) {
+      net_close_raw(s);
+      return OS_SOCKET_BAD;
+    }
+  }
+#ifdef _WIN32
+  nb = 0;
+  ioctlsocket(NET_FD(s), FIONBIO, &nb);
+#else
+  fcntl(s, F_SETFL, fl);
+#endif
+  return s;
+}
+
+os_socket_t os_net_accept(os_socket_t s, int timeout_ms, int *timed_out) {
+  if (timed_out)
+    *timed_out = 0;
+  int w = wait_io(s, 0, timeout_ms);
+  if (w == 0) {
+    if (timed_out)
+      *timed_out = 1;
+    return OS_SOCKET_BAD;
+  }
+  if (w < 0)
+    return OS_SOCKET_BAD;
+  os_socket_t c = (os_socket_t)accept(NET_FD(s), NULL, NULL);
+  if (c == OS_SOCKET_BAD)
+    return OS_SOCKET_BAD;
+  int one = 1;
+  setsockopt(NET_FD(c), IPPROTO_TCP, TCP_NODELAY, (const char *)&one,
+             sizeof(one));
+  return c;
+}
+
+long os_net_recv(os_socket_t s, void *buf, size_t n, int timeout_ms) {
+  int w = wait_io(s, 0, timeout_ms);
+  if (w == 0)
+    return -2;
+  if (w < 0)
+    return -1;
+  size_t want = n > (size_t)(1 << 20) ? (size_t)(1 << 20) : n;
+  int r = (int)recv(NET_FD(s), (char *)buf, (int)want, 0);
+  if (r == 0)
+    return 0;
+  if (r < 0)
+    return net_last_conn_reset() ? 0 : (net_last_would_block() ? -2 : -1);
+  return r;
+}
+
+int os_net_send_all(os_socket_t s, const void *buf, size_t n, int timeout_ms) {
+  const char *p = buf;
+  size_t off = 0;
+  while (off < n) {
+    int w = wait_io(s, 1, timeout_ms ? timeout_ms : NET_SEND_TIMEOUT_MS);
+    if (w <= 0)
+      return -1;
+    long r = (long)send(NET_FD(s), p + off, (int)(n - off), MSG_NOSIGNAL);
+    if (r <= 0) {
+      if (net_last_would_block())
+        continue;
+      return -1;
+    }
+    off += (size_t)r;
+  }
+  return 0;
+}
+
+void os_net_shutdown(os_socket_t s) {
+#ifdef _WIN32
+  shutdown((SOCKET)s, SD_BOTH);
+#else
+  shutdown(s, SHUT_RDWR);
+#endif
+}
+
+void os_net_close(os_socket_t s) {
+  if (s == OS_SOCKET_BAD)
+    return;
+  net_close_raw(s);
+}
diff --git a/src/web_md.c b/src/web_md.c
new file mode 100644
index 0000000..c204d6f
--- /dev/null
+++ b/src/web_md.c
@@ -0,0 +1,319 @@
+#ifndef _DEFAULT_SOURCE
+#define _DEFAULT_SOURCE
+#endif
+
+#include "cst_web_md.h"
+
+#include "cst_util.h"
+#include "sashidown.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct cst_web_md {
+  sashidown_stream_t *st;
+  cst_web_md_emit_fn emit;
+  void *ud;
+  cst_buf_t in;    /* HTML from sashidown, waiting for a complete tag */
+  int failed;
+};
+
+/* --- sanitizer ------------------------------------------------------------ */
+
+static const char *ALLOWED_TAGS[] = {
+    "p",      "br",     "hr",     "h1",     "h2",      "h3",     "h4",
+    "h5",     "h6",     "strong", "em",     "b",       "i",      "u",
+    "s",      "del",    "code",   "pre",    "blockquote", "ul",  "ol",
+    "li",     "table",  "thead",  "tbody",  "tr",      "th",     "td",
+    "a",      "img",    "span",   "div",    NULL};
+
+static int tag_allowed(const char *name, size_t n) {
+  for (int i = 0; ALLOWED_TAGS[i]; i++) {
+    if (strlen(ALLOWED_TAGS[i]) == n && strncmp(name, ALLOWED_TAGS[i], n) == 0)
+      return 1;
+  }
+  return 0;
+}
+
+/* A URL we are willing to put in href: http(s), mailto, or a same-site
+ * path. Anything else (javascript:, data:, file:, //evil) is dropped. */
+static int href_ok(const char *v, size_t n) {
+  if (n == 0)
+    return 0;
+  if (!strncmp(v, "http://", 7) || !strncmp(v, "https://", 8) ||
+      !strncmp(v, "mailto:", 7))
+    return 1;
+  if (v[0] == '/' && !(n > 1 && (v[1] == '/' || v[1] == '\\')))
+    return 1;
+  if (v[0] == '#')
+    return 1;
+  return 0;
+}
+
+static int src_ok(const char *v, size_t n) {
+  if (n > 11 && !strncmp(v, "data:image/", 11))
+    return 1;
+  if (n > 12 && !strncmp(v, "/api/attach/", 12))
+    return 1;
+  return 0;
+}
+
+static void attr_append(cst_buf_t *b, const char *name, size_t nlen,
+                        const char *val, size_t vlen) {
+  cst_buf_puts(b, " ");
+  cst_buf_append(b, name, nlen);
+  cst_buf_puts(b, "=\"");
+  cst_buf_append(b, val, vlen);
+  cst_buf_puts(b, "\"");
+}
+
+/* Rewrite one tag (open, close or self-closing) into out; may emit nothing
+ * when the tag is not allowed. Returns 0, or -1 on OOM. */
+static int sanitize_tag(const char *tag, size_t len, cst_buf_t *out) {
+  /* <name ...> or </name> or <!-- ... --> */
+  size_t i = 0;
+  int closing = 0;
+  if (len < 3 || tag[0] != '<')
+    return 0;
+  i = 1;
+  if (i < len && tag[i] == '/') {
+    closing = 1;
+    i++;
+  }
+  size_t name_start = i;
+  while (i < len && ((tag[i] >= 'a' && tag[i] <= 'z') ||
+                     (tag[i] >= 'A' && tag[i] <= 'Z') ||
+                     (tag[i] >= '0' && tag[i] <= '9')))
+    i++;
+  size_t name_len = i - name_start;
+  if (name_len == 0 || !tag_allowed(tag + name_start, name_len))
+    return 0; /* comments, <script>, <iframe>: dropped entirely */
+  int is_img = name_len == 3 && strncmp(tag + name_start, "img", 3) == 0;
+  int is_a = name_len == 1 && tag[name_start] == 'a';
+  int self_closing = len > 2 && tag[len - 2] == '/';
+  size_t start = out->len;
+  cst_buf_puts(out, "<");
+  if (closing)
+    cst_buf_puts(out, "/");
+  cst_buf_append(out, tag + name_start, name_len);
+  if (!closing) {
+    /* copy the allowed attributes */
+    int keep_target = 0; /* a link is only useful with a usable href */
+    size_t p = name_start + name_len;
+    while (p < len && tag[p] != '>' && !(tag[p] == '/' && p + 1 < len &&
+                                         tag[p + 1] == '>')) {
+      while (p < len && (tag[p] == ' ' || tag[p] == '\t' || tag[p] == '\n'))
+        p++;
+      size_t an = p;
+      while (p < len && tag[p] != '=' && tag[p] != ' ' && tag[p] != '\t' &&
+             tag[p] != '\n' && tag[p] != '>' && tag[p] != '/')
+        p++;
+      size_t an_len = p - an;
+      if (an_len == 0) {
+        p++;
+        continue;
+      }
+      const char *aval = "";
+      size_t av_len = 0;
+      if (p < len && tag[p] == '=') {
+        p++;
+        char quote = 0;
+        if (p < len && (tag[p] == '"' || tag[p] == '\''))
+          quote = tag[p++];
+        size_t as = p;
+        while (p < len &&
+               (quote ? tag[p] != quote : (tag[p] != ' ' && tag[p] != '>')))
+          p++;
+        aval = tag + as;
+        av_len = p - as;
+        if (quote && p < len)
+          p++; /* closing quote */
+      }
+      int keep = 0;
+      if (is_a && an_len == 4 && strncmp(tag + an, "href", 4) == 0) {
+        keep = href_ok(aval, av_len);
+        keep_target = keep;
+      } else if (is_img && an_len == 3 && strncmp(tag + an, "src", 3) == 0) {
+        keep = src_ok(aval, av_len);
+        keep_target = keep;
+      } else if (is_img && an_len == 3 && strncmp(tag + an, "alt", 3) == 0)
+        keep = 1;
+      else if (an_len == 5 && strncmp(tag + an, "class", 5) == 0 &&
+               av_len > 9 && !strncmp(aval, "language-", 9))
+        keep = 1;
+      if (keep)
+        attr_append(out, tag + an, an_len, aval, av_len);
+    }
+    if (is_a && keep_target) {
+      cst_buf_puts(out, " target=\"_blank\" rel=\"noopener noreferrer\"");
+    }
+    if ((is_a && !keep_target) || (is_img && !keep_target)) {
+      /* a link with an unusable href, or an image from nowhere: drop the
+       * whole tag and keep only its text */
+      out->len = start;
+      if (out->buf)
+        out->buf[start] = 0;
+      return 0;
+    }
+    cst_buf_puts(out, self_closing ? " /" : "");
+  }
+  cst_buf_puts(out, ">");
+  return 0;
+}
+
+/* Emit the text before every '<' and every tag through the sanitizer. */
+static void scan_chunk(cst_web_md_t *s, int final) {
+  if (!s->emit || s->failed)
+    return;
+  size_t i = 0, emitted = 0;
+  while (i < s->in.len) {
+    if (s->in.buf[i] != '<') {
+      i++;
+      continue;
+    }
+    size_t close = i;
+    while (close < s->in.len && s->in.buf[close] != '>')
+      close++;
+    if (close >= s->in.len && !final)
+      break; /* the tag may still be growing: keep it buffered */
+    if (i > emitted && s->emit(s->in.buf + emitted, i - emitted, s->ud) != 0)
+      s->failed = 1;
+    size_t tag_len = close >= s->in.len ? s->in.len - i : close - i + 1;
+    cst_buf_t tag = {0};
+    if (sanitize_tag(s->in.buf + i, tag_len, &tag) != 0) {
+      cst_buf_free(&tag);
+      s->failed = 1;
+      return;
+    }
+    if (tag.len && s->emit(tag.buf, tag.len, s->ud) != 0)
+      s->failed = 1;
+    cst_buf_free(&tag);
+    i = i + tag_len;
+    emitted = i;
+    if (s->failed)
+      break;
+  }
+  if (emitted > 0) {
+    memmove(s->in.buf, s->in.buf + emitted, s->in.len - emitted);
+    s->in.len -= emitted;
+    s->in.buf[s->in.len] = 0;
+  }
+}
+
+/* Collector used by the one-shot sanitizer. */
+typedef struct {
+  cst_buf_t *b;
+  int failed;
+} md_collect_t;
+
+static int collect_emit(const char *html, size_t len, void *ud) {
+  md_collect_t *c = ud;
+  if (cst_buf_append(c->b, html, len) != 0) {
+    c->failed = 1;
+    return 1;
+  }
+  return 0;
+}
+
+char *cst_web_md_sanitize(const char *html, size_t len) {
+  cst_web_md_t tmp;
+  memset(&tmp, 0, sizeof(tmp));
+  cst_buf_t out = {0};
+  md_collect_t col = {&out, 0};
+  if (cst_buf_append(&tmp.in, html ? html : "", len) != 0)
+    return NULL;
+  tmp.emit = collect_emit;
+  tmp.ud = &col;
+  scan_chunk(&tmp, 1);
+  cst_buf_free(&tmp.in);
+  if (col.failed) {
+    cst_buf_free(&out);
+    return NULL;
+  }
+  return cst_buf_steal(&out);
+}
+
+/* --- sashidown glue ------------------------------------------------------- */
+
+static int on_sashidown_html(const char *html, size_t len, void *user) {
+  cst_web_md_t *s = user;
+  if (cst_buf_append(&s->in, html, len) != 0) {
+    s->failed = 1;
+    return 1;
+  }
+  scan_chunk(s, 0);
+  return s->failed ? 1 : 0;
+}
+
+cst_web_md_t *cst_web_md_new(cst_web_md_emit_fn emit, void *ud) {
+  cst_web_md_t *s = calloc(1, sizeof(*s));
+  if (!s)
+    return NULL;
+  sashidown_stream_opts_t opts;
+  memset(&opts, 0, sizeof(opts));
+  opts.on_html = on_sashidown_html;
+  opts.user = s;
+  s->st = sashidown_stream_create(&opts);
+  if (!s->st) {
+    free(s);
+    return NULL;
+  }
+  s->emit = emit;
+  s->ud = ud;
+  return s;
+}
+
+int cst_web_md_feed(cst_web_md_t *s, const char *data, size_t len) {
+  if (!s || !s->st)
+    return -1;
+  if (len && sashidown_stream_feed(s->st, data, len) != 0) {
+    s->failed = 1;
+    return -1;
+  }
+  return s->failed ? -1 : 0;
+}
+
+int cst_web_md_finish(cst_web_md_t *s) {
+  if (!s || !s->st)
+    return -1;
+  if (sashidown_stream_finish(s->st) != 0) {
+    s->failed = 1;
+    return -1;
+  }
+  scan_chunk(s, 1);
+  return s->failed ? -1 : 0;
+}
+
+void cst_web_md_free(cst_web_md_t *s) {
+  if (!s)
+    return;
+  if (s->st)
+    sashidown_stream_destroy(s->st);
+  cst_buf_free(&s->in);
+  free(s);
+}
+
+char *cst_web_md_html(const char *md, size_t len) {
+  if (!md)
+    return NULL;
+  size_t cap = 65536;
+  char *out = NULL;
+  for (int attempt = 0; attempt < 8; attempt++) {
+    char *buf = malloc(cap);
+    if (!buf)
+      return NULL;
+    size_t out_len = 0;
+    if (sashidown_convert(md, len, buf, cap, &out_len, SASHIDOWN_FMT_HTML) ==
+        0) {
+      out = cst_web_md_sanitize(buf, out_len);
+      free(buf);
+      return out;
+    }
+    free(buf);
+    if (cap >= (size_t)8 * 1024 * 1024)
+      break;
+    cap *= 2;
+  }
+  return NULL;
+}
diff --git a/src/webui.c b/src/webui.c
new file mode 100644
index 0000000..593c934
--- /dev/null
+++ b/src/webui.c
@@ -0,0 +1,1257 @@
+/* WebUI: the HTTP + SSE front end (see include/cst_webui.h).
+ *
+ * Threading: every HTTP connection runs on its own thread (src/http_srv.c),
+ * a turn runs on its own worker thread, and the agent itself is only ever
+ * touched from the turn thread or while holding w->mu. The hooks the agent
+ * calls live on the turn thread: they append to the event ring, wake the
+ * event-stream threads and, for permission/ask_user, block until the
+ * browser answers (or the timeout denies it). Nothing in the engine was
+ * changed to make this work - the hooks are the interface the TUI uses too. */
+
+#ifndef _DEFAULT_SOURCE
+#define _DEFAULT_SOURCE
+#endif
+
+#include "cst_agent.h"
+#include "cst_attach.h"
+#include "cst_http.h"
+#include "cst_util.h"
+#include "cst_web_md.h"
+#include "cst_webui.h"
+#include "cJSON.h"
+#include "os_compat.h"
+
+#include <pthread.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+#define WUI_RING 2000
+#define WUI_TOOL_OUT 32768
+#define WUI_ASK_MAX 1024
+
+typedef struct {
+  const char *name;
+  const char *ctype;
+  const unsigned char *data;
+  size_t len;
+} wui_asset_t;
+
+#include "web_assets.inc"
+
+typedef struct wui_sse {
+  struct wui *w;
+  cst_http_conn_t *c;
+  uint64_t cursor;
+  pthread_mutex_t mu;
+  pthread_cond_t cv;
+  int closed;
+  struct wui_sse *next;
+} wui_sse_t;
+
+typedef struct wui {
+  cst_agent_t *agent;
+  cst_http_server_t *srv;
+  char host[64];
+  char token[64];
+  int need_auth;
+  const char *root; /* --web-dev: serve assets from disk */
+  int perm_timeout_s;
+
+  pthread_mutex_t mu;
+  pthread_cond_t cv; /* permission / ask_user answers */
+  cst_web_md_t *md; /* live markdown for the running turn */
+  /* event ring */
+  uint64_t seq;
+  struct {
+    uint64_t seq;
+    char *frame;
+  } ring[WUI_RING];
+  wui_sse_t *subs;
+
+  int busy;
+  uint64_t req_id; /* permission/ask id counter */
+  uint64_t perm_id;
+  int perm_active, perm_answer;
+  uint64_t ask_id;
+  int ask_active, ask_rc;
+  char ask_ans[WUI_ASK_MAX];
+
+  volatile int stopping;
+} wui_t;
+
+/* --- events --------------------------------------------------------------- */
+
+static uint64_t wui_first_seq(const wui_t *w) {
+  return w->seq > WUI_RING ? w->seq - WUI_RING + 1 : 1;
+}
+
+/* Owns data (a cJSON object). */
+static void wui_emit(wui_t *w, const char *type, cJSON *data) {
+  if (!data)
+    data = cJSON_CreateObject();
+  if (!data)
+    return;
+  cJSON_AddStringToObject(data, "type", type);
+  cJSON_AddNumberToObject(data, "seq", (double)(w->seq + 1));
+  char *json = cJSON_PrintUnformatted(data);
+  cJSON_Delete(data);
+  if (!json)
+    return;
+  cst_buf_t f = {0};
+  cst_buf_printf(&f, "event: %s\ndata: %s\n\n", type, json);
+  free(json);
+  if (!f.buf) {
+    cst_buf_free(&f);
+    return;
+  }
+  pthread_mutex_lock(&w->mu);
+  w->seq++;
+  int slot = (int)(w->seq % WUI_RING);
+  free(w->ring[slot].frame);
+  w->ring[slot].frame = f.buf; /* stolen */
+  w->ring[slot].seq = w->seq;
+  f.buf = NULL;
+  for (wui_sse_t *s = w->subs; s; s = s->next)
+    pthread_cond_broadcast(&s->cv);
+  pthread_mutex_unlock(&w->mu);
+  cst_buf_free(&f);
+}
+
+static void wui_emit_str(wui_t *w, const char *type, const char *key,
+                         const char *val) {
+  cJSON *o = cJSON_CreateObject();
+  if (!o)
+    return;
+  cJSON_AddStringToObject(o, key, val ? val : "");
+  wui_emit(w, type, o);
+}
+
+static void wui_emit_text(wui_t *w, const char *type, const char *text,
+                          size_t len) {
+  cJSON *o = cJSON_CreateObject();
+  if (!o)
+    return;
+  char *s = malloc(len + 1);
+  if (!s) {
+    cJSON_Delete(o);
+    return;
+  }
+  memcpy(s, text, len);
+  s[len] = 0;
+  cJSON_AddStringToObject(o, "text", s);
+  free(s);
+  wui_emit(w, type, o);
+}
+
+/* --- state --------------------------------------------------------------- */
+
+static cJSON *wui_state_new(wui_t *w) {
+  const cst_agent_config_t *cfg = cst_agent_config(w->agent);
+  cJSON *o = cJSON_CreateObject();
+  if (!o || !cfg) {
+    cJSON_Delete(o);
+    return NULL;
+  }
+  char sid[128] = "";
+  cst_agent_session_id(w->agent, sid, sizeof(sid));
+  cst_usage_t sess = {0}, turn = {0};
+  cst_agent_usage(w->agent, &sess, &turn);
+  cJSON_AddStringToObject(o, "protocol", "cst-webui/1");
+  cJSON_AddStringToObject(o, "workspace", cfg->workspace_root);
+  cJSON_AddStringToObject(o, "session", sid);
+  cJSON_AddStringToObject(o, "provider", cfg->provider);
+  cJSON_AddStringToObject(o, "model", cfg->model);
+  cJSON_AddStringToObject(o, "effort", cfg->effort);
+  cJSON_AddStringToObject(o, "approval", cst_approval_name(cfg->approval));
+  cJSON_AddStringToObject(o, "protocol_tools", cst_protocol_name(cfg->protocol));
+  cJSON_AddBoolToObject(o, "plan_mode", cfg->plan_mode);
+  cJSON_AddBoolToObject(o, "status_busy", w->busy);
+  cJSON_AddStringToObject(o, "todo", cst_agent_todo(w->agent)
+                                       ? cst_agent_todo(w->agent)
+                                       : "");
+  cJSON_AddNumberToObject(o, "context_tokens",
+                          (double)cst_agent_last_prompt_tokens(w->agent));
+  cJSON_AddBoolToObject(o, "undo_available",
+                        cst_agent_undo_available(w->agent) != 0);
+  cJSON *u = cJSON_AddObjectToObject(o, "usage");
+  if (u) {
+    cJSON_AddNumberToObject(u, "requests", sess.requests);
+    cJSON_AddNumberToObject(u, "prompt_tokens", (double)sess.prompt);
+    cJSON_AddNumberToObject(u, "completion_tokens", (double)sess.out);
+    cJSON_AddNumberToObject(u, "cost", sess.cost);
+    cJSON_AddBoolToObject(u, "priced", sess.priced != 0);
+    cJSON_AddStringToObject(u, "currency", sess.currency);
+  }
+  cJSON *imgs = cJSON_AddArrayToObject(o, "pending_images");
+  int n = cst_agent_pending_count(w->agent);
+  for (int i = 0; i < n && imgs; i++) {
+    char line[160];
+    if (cst_agent_pending_describe(w->agent, i, line, sizeof(line)) == 0)
+      cJSON_AddItemToArray(imgs, cJSON_CreateString(line));
+  }
+  return o;
+}
+
+static void wui_emit_state(wui_t *w) {
+  cJSON *o = wui_state_new(w);
+  if (o)
+    wui_emit(w, "state", o);
+}
+
+/* --- session -------------------------------------------------------------- */
+
+static cJSON *msg_json(const cst_message_t *m) {
+  cJSON *o = cJSON_CreateObject();
+  if (!o)
+    return NULL;
+  const char *role = "user";
+  switch (m->role) {
+  case CST_ROLE_SYSTEM: role = "system"; break;
+  case CST_ROLE_ASSISTANT: role = "assistant"; break;
+  case CST_ROLE_TOOL: role = "tool"; break;
+  default: role = "user"; break;
+  }
+  cJSON_AddStringToObject(o, "role", role);
+  cJSON_AddStringToObject(o, "content", m->content ? m->content : "");
+  if (m->role == CST_ROLE_ASSISTANT && m->content && m->content[0]) {
+    char *html = cst_web_md_html(m->content, strlen(m->content));
+    if (html) {
+      cJSON_AddStringToObject(o, "html", html);
+      free(html);
+    }
+  }
+  if (m->reasoning && m->reasoning[0])
+    cJSON_AddStringToObject(o, "reasoning", m->reasoning);
+  if (m->tool_call_id[0])
+    cJSON_AddStringToObject(o, "tool_call_id", m->tool_call_id);
+  if (m->tool_name[0])
+    cJSON_AddStringToObject(o, "tool_name", m->tool_name);
+  if (m->tool_calls_json && m->tool_calls_json[0]) {
+    cJSON *tc = cJSON_Parse(m->tool_calls_json);
+    if (tc) {
+      cJSON_AddItemToObject(o, "tool_calls", tc);
+    }
+  }
+  if (m->nattach > 0) {
+    cJSON *arr = cJSON_AddArrayToObject(o, "attach");
+    for (int i = 0; arr && i < m->nattach; i++) {
+      cJSON *a = cJSON_CreateObject();
+      if (!a)
+        continue;
+      cJSON_AddStringToObject(a, "name", m->attach[i].name);
+      cJSON_AddStringToObject(a, "mime", m->attach[i].mime);
+      cJSON_AddStringToObject(a, "rel", m->attach[i].rel);
+      cJSON_AddNumberToObject(a, "bytes", (double)m->attach[i].bytes);
+      cJSON_AddItemToArray(arr, a);
+    }
+  }
+  return o;
+}
+
+static char *wui_session_json(wui_t *w, int from) {
+  cst_session_t *s = cst_agent_session(w->agent);
+  if (!s)
+    return NULL;
+  cJSON *root = cJSON_CreateObject();
+  if (!root)
+    return NULL;
+  cJSON *arr = cJSON_AddArrayToObject(root, "messages");
+  cst_session_lock(s);
+  int n = cst_session_count(s);
+  for (int i = from; i < n; i++) {
+    const cst_message_t *m = cst_session_get(s, i);
+    if (!m)
+      continue;
+    cJSON *j = msg_json(m);
+    if (j && arr)
+      cJSON_AddItemToArray(arr, j);
+    else
+      cJSON_Delete(j);
+  }
+  cst_session_unlock(s);
+  char *out = cJSON_PrintUnformatted(root);
+  cJSON_Delete(root);
+  return out;
+}
+
+/* --- hooks --------------------------------------------------------------- */
+
+static int wui_md_emit(const char *html, size_t len, void *ud) {
+  wui_t *w = ud;
+  if (len)
+    wui_emit_text(w, "assistant_html", html, len);
+  return 0;
+}
+
+static void on_status(const char *msg, void *ud) {
+  wui_emit_str((wui_t *)ud, "status", "message", msg);
+}
+
+static void on_assistant_delta(const char *text, size_t len, void *ud) {
+  wui_t *w = ud;
+  if (!w->md)
+    w->md = cst_web_md_new(wui_md_emit, w);
+  if (w->md)
+    cst_web_md_feed(w->md, text, len);
+  wui_emit_text(w, "assistant_delta", text, len);
+}
+
+static void on_think_delta(const char *text, size_t len, void *ud) {
+  wui_emit_text((wui_t *)ud, "think_delta", text, len);
+}
+
+static cJSON *call_json(const ctl_tool_call_t *call) {
+  cJSON *o = cJSON_CreateObject();
+  if (!o)
+    return NULL;
+  cJSON_AddStringToObject(o, "id", call->id);
+  cJSON_AddStringToObject(o, "name", call->name);
+  cJSON *args = cJSON_AddObjectToObject(o, "args");
+  for (int i = 0; args && i < call->nargs; i++) {
+    cJSON *v = cJSON_CreateString(call->args[i].value ? call->args[i].value : "");
+    if (v)
+      cJSON_AddItemToObject(args, call->args[i].key, v);
+  }
+  return o;
+}
+
+static void on_tool_event(const char *phase, const ctl_tool_call_t *call,
+                          const char *detail, void *ud) {
+  wui_t *w = ud;
+  cJSON *o = call ? call_json(call) : cJSON_CreateObject();
+  if (!o)
+    return;
+  cJSON_AddStringToObject(o, "phase", phase ? phase : "");
+  if (detail)
+    cJSON_AddStringToObject(o, "detail", detail);
+  wui_emit(w, "tool", o);
+}
+
+static void on_tool_result(const ctl_tool_call_t *call, const char *out,
+                           size_t len, int exit_code, void *ud) {
+  wui_t *w = ud;
+  cJSON *o = call ? call_json(call) : cJSON_CreateObject();
+  if (!o)
+    return;
+  size_t shown = len > WUI_TOOL_OUT ? WUI_TOOL_OUT : len;
+  char *s = malloc(shown + 1);
+  if (!s) {
+    cJSON_Delete(o);
+    return;
+  }
+  memcpy(s, out, shown);
+  s[shown] = 0;
+  cJSON_AddStringToObject(o, "out", s);
+  cJSON_AddBoolToObject(o, "truncated", len > shown);
+  cJSON_AddNumberToObject(o, "bytes", (double)len);
+  free(s);
+  cJSON_AddNumberToObject(o, "exit", exit_code);
+  wui_emit(w, "tool_result", o);
+}
+
+static void on_todo(const char *text, void *ud) {
+  wui_emit_str((wui_t *)ud, "todo", "text", text ? text : "");
+}
+
+static int wui_wait_permission(wui_t *w, const char *tool, const char *detail,
+                               const char *preview) {
+  pthread_mutex_lock(&w->mu);
+  w->req_id++;
+  uint64_t id = w->req_id;
+  w->perm_id = id;
+  w->perm_active = 1;
+  w->perm_answer = -1;
+  int has_client = w->subs != NULL;
+  pthread_mutex_unlock(&w->mu);
+
+  cJSON *o = cJSON_CreateObject();
+  if (o) {
+    cJSON_AddNumberToObject(o, "id", (double)id);
+    cJSON_AddStringToObject(o, "tool", tool ? tool : "tool");
+    cJSON_AddStringToObject(o, "detail", detail ? detail : "");
+    cJSON_AddStringToObject(o, "preview", preview ? preview : "");
+    cJSON_AddBoolToObject(o, "sandbox", detail &&
+                                           strncmp(detail, CST_PERM_SANDBOX,
+                                                   strlen(CST_PERM_SANDBOX)) ==
+                                               0);
+    wui_emit(w, "permission", o);
+  }
+  int timeout = w->perm_timeout_s > 0 ? w->perm_timeout_s : 600;
+  /* Nobody is watching: do not hang the turn for ten minutes. */
+  if (!has_client)
+    timeout = 3;
+  int answer = CST_PERM_DENY;
+  struct timespec deadline;
+  clock_gettime(CLOCK_REALTIME, &deadline);
+  deadline.tv_sec += timeout;
+  pthread_mutex_lock(&w->mu);
+  for (;;) {
+    if (w->perm_active && w->perm_id == id && w->perm_answer >= 0) {
+      answer = w->perm_answer;
+      w->perm_active = 0;
+      break;
+    }
+    if (w->stopping)
+      break;
+    int rc = pthread_cond_timedwait(&w->cv, &w->mu, &deadline);
+    if (rc != 0) {
+      w->perm_active = 0;
+      break;
+    }
+  }
+  pthread_mutex_unlock(&w->mu);
+  cJSON *e = cJSON_CreateObject();
+  if (e) {
+    cJSON_AddNumberToObject(e, "id", (double)id);
+    cJSON_AddNumberToObject(e, "answer", answer);
+    wui_emit(w, "permission_done", e);
+  }
+  return answer;
+}
+
+static int on_permission(const char *tool_name, const char *detail,
+                         const char *preview, void *ud) {
+  return wui_wait_permission((wui_t *)ud, tool_name, detail, preview);
+}
+
+static int on_ask_user(const char *question, const char *options, char *ans,
+                       size_t ans_sz, void *ud) {
+  wui_t *w = ud;
+  pthread_mutex_lock(&w->mu);
+  w->req_id++;
+  uint64_t id = w->req_id;
+  w->ask_id = id;
+  w->ask_active = 1;
+  w->ask_rc = -1;
+  w->ask_ans[0] = 0;
+  int has_client = w->subs != NULL;
+  pthread_mutex_unlock(&w->mu);
+
+  cJSON *o = cJSON_CreateObject();
+  if (o) {
+    cJSON_AddNumberToObject(o, "id", (double)id);
+    cJSON_AddStringToObject(o, "question", question ? question : "");
+    cJSON *arr = cJSON_AddArrayToObject(o, "options");
+    for (const char *p = options; arr && p && *p;) {
+      const char *nl = strchr(p, '\n');
+      size_t n = nl ? (size_t)(nl - p) : strlen(p);
+      char *tmp = malloc(n + 1);
+      if (tmp) {
+        memcpy(tmp, p, n);
+        tmp[n] = 0;
+        cJSON_AddItemToArray(arr, cJSON_CreateString(tmp));
+        free(tmp);
+      }
+      p = nl ? nl + 1 : NULL;
+    }
+    wui_emit(w, "ask_user", o);
+  }
+  int timeout = has_client ? 600 : 3;
+  int rc = -1;
+  struct timespec deadline;
+  clock_gettime(CLOCK_REALTIME, &deadline);
+  deadline.tv_sec += timeout;
+  pthread_mutex_lock(&w->mu);
+  for (;;) {
+    if (w->ask_active && w->ask_id == id && w->ask_rc != 0) {
+      rc = w->ask_rc == 1 ? 0 : -1;
+      snprintf(ans, ans_sz, "%s", w->ask_ans);
+      w->ask_active = 0;
+      break;
+    }
+    if (w->stopping)
+      break;
+    int wrc = pthread_cond_timedwait(&w->cv, &w->mu, &deadline);
+    if (wrc != 0) {
+      w->ask_active = 0;
+      break;
+    }
+  }
+  pthread_mutex_unlock(&w->mu);
+  return rc;
+}
+
+/* --- routes -------------------------------------------------------------- */
+
+static int read_file_all(const char *path, char **out, size_t *out_len) {
+  FILE *fp = fopen(path, "rb");
+  if (!fp)
+    return -1;
+  cst_buf_t b = {0};
+  char tmp[8192];
+  size_t n;
+  while ((n = fread(tmp, 1, sizeof(tmp), fp)) > 0) {
+    if (cst_buf_append(&b, tmp, n) != 0) {
+      fclose(fp);
+      cst_buf_free(&b);
+      return -1;
+    }
+  }
+  fclose(fp);
+  size_t total = b.len;
+  *out = cst_buf_steal(&b);
+  if (!*out)
+    return -1;
+  *out_len = total;
+  return 0;
+}
+
+static int wui_serve_file(cst_http_conn_t *c, wui_t *w, const char *path) {
+  if (!w->root || !path || !path[0] || strstr(path, ".."))
+    return -1;
+  char full[4096];
+  const char *rel = path[0] == '/' ? path + 1 : path;
+  if (!rel[0])
+    rel = "index.html";
+  if (snprintf(full, sizeof(full), "%s/%s", w->root, rel) >=
+      (int)sizeof(full))
+    return -1;
+  char *data = NULL;
+  size_t len = 0;
+  if (read_file_all(full, &data, &len) != 0)
+    return -1;
+  const char *ctype = "application/octet-stream";
+  size_t n = strlen(rel);
+  if (n > 5 && strcmp(rel + n - 5, ".html") == 0)
+    ctype = "text/html; charset=utf-8";
+  else if (n > 3 && strcmp(rel + n - 3, ".js") == 0)
+    ctype = "text/javascript; charset=utf-8";
+  else if (n > 4 && strcmp(rel + n - 4, ".css") == 0)
+    ctype = "text/css; charset=utf-8";
+  else if (n > 4 && strcmp(rel + n - 4, ".svg") == 0)
+    ctype = "image/svg+xml";
+  int rc = cst_http_send(c, 200, ctype, data, len);
+  free(data);
+  return rc;
+}
+
+static int wui_serve_asset(cst_http_conn_t *c, wui_t *w, const char *path) {
+  const char *rel = path[0] == '/' ? path + 1 : path;
+  if (!rel[0])
+    rel = "index.html";
+  if (w->root)
+    return wui_serve_file(c, w, path);
+  for (int i = 0; i < wui_asset_count; i++) {
+    if (strcmp(wui_assets[i].name, rel) == 0)
+      return cst_http_send(c, 200, wui_assets[i].ctype, wui_assets[i].data,
+                           wui_assets[i].len);
+  }
+  return -1;
+}
+
+static int h_asset(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  const cst_http_req_t *req = cst_http_request(c);
+  /* Stored session images: /api/attach/<rel>. The name is validated before
+   * it can touch the filesystem, and only the session's own directory is
+   * reachable. */
+  static const char prefix[] = "/api/attach/";
+  if (strncmp(req->path, prefix, sizeof(prefix) - 1) == 0) {
+    const char *rel = req->path + sizeof(prefix) - 1;
+    if (!cst_attach_rel_ok(rel))
+      return -1;
+    const char *sess = cst_agent_session_path(w->agent);
+    char dir[OS_PATH_MAX], full[OS_PATH_MAX];
+    if (!sess || cst_attach_dir(sess, dir, sizeof(dir)) != 0)
+      return -1;
+    if (snprintf(full, sizeof(full), "%s/%s", dir, rel) >= (int)sizeof(full))
+      return -1;
+    char *data = NULL;
+    size_t len = 0;
+    if (read_file_all(full, &data, &len) != 0)
+      return -1;
+    const char *ctype = "application/octet-stream";
+    size_t n = strlen(rel);
+    if (n > 4 && strcmp(rel + n - 4, ".png") == 0)
+      ctype = "image/png";
+    else if (n > 4 && (strcmp(rel + n - 4, ".jpg") == 0 ||
+                       strcmp(rel + n - 4, ".jpeg") == 0))
+      ctype = "image/jpeg";
+    else if (n > 4 && strcmp(rel + n - 4, ".gif") == 0)
+      ctype = "image/gif";
+    else if (n > 5 && strcmp(rel + n - 5, ".webp") == 0)
+      ctype = "image/webp";
+    else if (n > 4 && strcmp(rel + n - 4, ".bmp") == 0)
+      ctype = "image/bmp";
+    int rc = cst_http_send(c, 200, ctype, data, len);
+    free(data);
+    return rc;
+  }
+  return wui_serve_asset(c, w, req->path);
+}
+
+/* --- API handlers -------------------------------------------------------- */
+
+static int h_state(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  pthread_mutex_lock(&w->mu);
+  cJSON *o = wui_state_new(w);
+  pthread_mutex_unlock(&w->mu);
+  if (!o)
+    return cst_http_send_err(c, 500, "out of memory");
+  char *json = cJSON_PrintUnformatted(o);
+  cJSON_Delete(o);
+  if (!json)
+    return cst_http_send_err(c, 500, "out of memory");
+  int rc = cst_http_send_json(c, 200, json);
+  free(json);
+  return rc;
+}
+
+static int h_session(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  char buf[32];
+  int from = 0;
+  if (cst_http_query(cst_http_request(c), "from", buf, sizeof(buf)) == 0)
+    from = atoi(buf);
+  if (from < 0)
+    from = 0;
+  char *json = wui_session_json(w, from);
+  if (!json)
+    return cst_http_send_err(c, 500, "out of memory");
+  int rc = cst_http_send_json(c, 200, json);
+  free(json);
+  return rc;
+}
+
+static int h_events(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  const cst_http_req_t *req = cst_http_request(c);
+  wui_sse_t s;
+  memset(&s, 0, sizeof(s));
+  s.w = w;
+  s.c = c;
+  s.cursor = 0;
+  char buf[32];
+  if (cst_http_query(req, "since", buf, sizeof(buf)) == 0)
+    s.cursor = (uint64_t)strtoull(buf, NULL, 10);
+  pthread_mutex_init(&s.mu, NULL);
+  pthread_cond_init(&s.cv, NULL);
+  pthread_mutex_lock(&w->mu);
+  if (s.cursor == 0)
+    s.cursor = w->seq; /* a fresh client wants new events only */
+  if (s.cursor < wui_first_seq(w) - 1)
+    s.cursor = wui_first_seq(w) - 1; /* too far behind: resume at the head */
+  s.next = w->subs;
+  w->subs = &s;
+  pthread_mutex_unlock(&w->mu);
+
+  if (cst_http_stream_begin(c, "text/event-stream; charset=utf-8") != 0) {
+    goto done;
+  }
+  cst_http_stream_write(c, ": cst-agent webui\n\n", 19);
+  for (;;) {
+    if (cst_http_stopping(w->srv) || w->stopping || s.closed)
+      break;
+    cst_buf_t out = {0};
+    pthread_mutex_lock(&w->mu);
+    uint64_t last = w->seq;
+    uint64_t first = wui_first_seq(w);
+    int n = 0;
+    for (uint64_t q = s.cursor + 1; q <= last && n < 256; q++) {
+      if (q < first)
+        continue;
+      char *frame = w->ring[q % WUI_RING].frame;
+      if (!frame)
+        continue;
+      cst_buf_printf(&out, "id: %llu\n%s", (unsigned long long)q, frame);
+      n++;
+      s.cursor = q;
+    }
+    pthread_mutex_unlock(&w->mu);
+    if (n == 0) {
+      struct timespec ts;
+      clock_gettime(CLOCK_REALTIME, &ts);
+      ts.tv_sec += 1;
+      pthread_mutex_lock(&s.mu);
+      if (!s.closed)
+        pthread_cond_timedwait(&s.cv, &s.mu, &ts);
+      pthread_mutex_unlock(&s.mu);
+      cst_buf_free(&out);
+      if (cst_http_stream_write(c, ": ping\n\n", 8) != 0)
+        break;
+      continue;
+    }
+    int rc = cst_http_stream_write(c, out.buf, out.len);
+    cst_buf_free(&out);
+    if (rc != 0)
+      break;
+  }
+done:
+  pthread_mutex_lock(&w->mu);
+  wui_sse_t **pp = &w->subs;
+  while (*pp && *pp != &s)
+    pp = &(*pp)->next;
+  if (*pp == &s)
+    *pp = s.next;
+  pthread_mutex_unlock(&w->mu);
+  pthread_mutex_destroy(&s.mu);
+  pthread_cond_destroy(&s.cv);
+  return 0;
+}
+
+typedef struct {
+  wui_t *w;
+  char *prompt;
+} wui_turn_t;
+
+static void wui_end_turn(wui_t *w, int rc, const char *err) {
+  /* Flush the markdown *outside* the lock: flushing emits the last HTML
+   * chunks, and wui_emit takes w->mu itself. */
+  pthread_mutex_lock(&w->mu);
+  cst_web_md_t *md = w->md;
+  w->md = NULL;
+  w->busy = 0;
+  pthread_mutex_unlock(&w->mu);
+  if (md) {
+    cst_web_md_finish(md);
+    cst_web_md_free(md);
+  }
+  cJSON *o = cJSON_CreateObject();
+  if (o) {
+    cJSON_AddNumberToObject(o, "rc", rc);
+    cJSON_AddStringToObject(o, "error", err ? err : "");
+    wui_emit(w, "turn_end", o);
+  }
+  wui_emit_state(w);
+}
+
+static void *wui_turn_main(void *arg) {
+  wui_turn_t *t = arg;
+  wui_t *w = t->w;
+  cst_agent_hooks_t hooks;
+  memset(&hooks, 0, sizeof(hooks));
+  hooks.on_status = on_status;
+  hooks.on_assistant_delta = on_assistant_delta;
+  hooks.on_think_delta = on_think_delta;
+  hooks.on_tool_event = on_tool_event;
+  hooks.on_tool_result = on_tool_result;
+  hooks.on_permission = on_permission;
+  hooks.on_ask_user = on_ask_user;
+  hooks.on_todo = on_todo;
+  hooks.userdata = w;
+  char err[512];
+  err[0] = 0;
+  int rc = cst_agent_run_turn_ex(w->agent, t->prompt, &hooks, err, sizeof(err));
+  wui_end_turn(w, rc, err);
+  free(t->prompt);
+  free(t);
+  return NULL;
+}
+
+static int wui_start_turn(wui_t *w, const char *text, char *err, size_t err_sz) {
+  pthread_mutex_lock(&w->mu);
+  if (w->busy) {
+    pthread_mutex_unlock(&w->mu);
+    snprintf(err, err_sz, "a turn is already running");
+    return -1;
+  }
+  w->busy = 1;
+  if (w->md) {
+    cst_web_md_free(w->md);
+    w->md = NULL;
+  }
+  pthread_mutex_unlock(&w->mu);
+  wui_turn_t *t = calloc(1, sizeof(*t));
+  if (!t) {
+    pthread_mutex_lock(&w->mu);
+    w->busy = 0;
+    pthread_mutex_unlock(&w->mu);
+    snprintf(err, err_sz, "out of memory");
+    return -1;
+  }
+  t->w = w;
+  t->prompt = strdup(text ? text : "");
+  if (!t->prompt) {
+    free(t);
+    pthread_mutex_lock(&w->mu);
+    w->busy = 0;
+    pthread_mutex_unlock(&w->mu);
+    snprintf(err, err_sz, "out of memory");
+    return -1;
+  }
+  pthread_t th;
+  if (pthread_create(&th, NULL, wui_turn_main, t) != 0) {
+    free(t->prompt);
+    free(t);
+    pthread_mutex_lock(&w->mu);
+    w->busy = 0;
+    pthread_mutex_unlock(&w->mu);
+    snprintf(err, err_sz, "cannot start the turn thread");
+    return -1;
+  }
+  pthread_detach(th);
+  wui_emit_state(w);
+  return 0;
+}
+
+static int h_turn(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  const cst_http_req_t *req = cst_http_request(c);
+  cJSON *body = req->body_len ? cJSON_Parse(req->body) : NULL;
+  const cJSON *text = body ? cJSON_GetObjectItem(body, "text") : NULL;
+  if (!body || !cJSON_IsString(text)) {
+    cJSON_Delete(body);
+    return cst_http_send_err(c, 400, "expected {\"text\": \"...\"}");
+  }
+  char err[256] = "";
+  int rc = wui_start_turn(w, text->valuestring, err, sizeof(err));
+  cJSON_Delete(body);
+  if (rc != 0)
+    return cst_http_send_err(c, 409, err);
+  return cst_http_send_str(c, 202, "application/json; charset=utf-8",
+                           "{\"ok\":true}");
+}
+
+static int h_cancel(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  cst_agent_request_cancel(w->agent);
+  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
+                           "{\"ok\":true}");
+}
+
+static int h_permission(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  const cst_http_req_t *req = cst_http_request(c);
+  cJSON *body = req->body_len ? cJSON_Parse(req->body) : NULL;
+  const cJSON *id = body ? cJSON_GetObjectItem(body, "id") : NULL;
+  const cJSON *ans = body ? cJSON_GetObjectItem(body, "answer") : NULL;
+  int ok = 0;
+  if (cJSON_IsNumber(id) && cJSON_IsNumber(ans)) {
+    int answer = (int)ans->valuedouble;
+    if (answer >= CST_PERM_DENY && answer <= CST_PERM_ALWAYS_PREFIX) {
+      pthread_mutex_lock(&w->mu);
+      if (w->perm_active && w->perm_id == (uint64_t)id->valuedouble) {
+        w->perm_answer = answer;
+        pthread_cond_broadcast(&w->cv);
+        ok = 1;
+      }
+      pthread_mutex_unlock(&w->mu);
+    }
+  }
+  cJSON_Delete(body);
+  if (!ok)
+    return cst_http_send_err(c, 409, "no such permission request");
+  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
+                           "{\"ok\":true}");
+}
+
+static int h_ask_user(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  const cst_http_req_t *req = cst_http_request(c);
+  cJSON *body = req->body_len ? cJSON_Parse(req->body) : NULL;
+  const cJSON *id = body ? cJSON_GetObjectItem(body, "id") : NULL;
+  const cJSON *text = body ? cJSON_GetObjectItem(body, "text") : NULL;
+  const cJSON *dismissed = body ? cJSON_GetObjectItem(body, "dismiss") : NULL;
+  int ok = 0;
+  if (cJSON_IsNumber(id)) {
+    pthread_mutex_lock(&w->mu);
+    if (w->ask_active && w->ask_id == (uint64_t)id->valuedouble) {
+      snprintf(w->ask_ans, sizeof(w->ask_ans), "%s",
+               cJSON_IsString(text) ? text->valuestring : "");
+      w->ask_rc = (dismissed && cJSON_IsTrue(dismissed)) ? -1 : 1;
+      pthread_cond_broadcast(&w->cv);
+      ok = 1;
+    }
+    pthread_mutex_unlock(&w->mu);
+  }
+  cJSON_Delete(body);
+  if (!ok)
+    return cst_http_send_err(c, 409, "no such question");
+  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
+                           "{\"ok\":true}");
+}
+
+static int h_sessions(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  const cst_agent_config_t *cfg = cst_agent_config(w->agent);
+  static char ids[200][128];
+  int n = cst_agent_store_list(cfg->workspace_root, ids, 200);
+  cJSON *root = cJSON_CreateObject();
+  if (!root)
+    return cst_http_send_err(c, 500, "out of memory");
+  char cur[128] = "";
+  cst_agent_store_get_current(cfg->workspace_root, cur, sizeof(cur));
+  cJSON_AddStringToObject(root, "current", cur);
+  cJSON *arr = cJSON_AddArrayToObject(root, "sessions");
+  for (int i = 0; arr && i < n; i++) {
+    cst_session_info_t in;
+    if (cst_agent_store_info(cfg->workspace_root, ids[i], &in) != 0)
+      continue;
+    cJSON *o = cJSON_CreateObject();
+    if (!o)
+      continue;
+    cJSON_AddStringToObject(o, "id", in.id);
+    cJSON_AddStringToObject(o, "title",
+                            in.title[0] ? in.title : in.first_user);
+    cJSON_AddNumberToObject(o, "messages", in.messages);
+    cJSON_AddNumberToObject(o, "mtime", (double)in.mtime);
+    cJSON_AddItemToArray(arr, o);
+  }
+  char *json = cJSON_PrintUnformatted(root);
+  cJSON_Delete(root);
+  int rc = cst_http_send_json(c, 200, json);
+  free(json);
+  return rc;
+}
+
+static int h_session_new(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  char id[128] = "";
+  if (cst_agent_new_session(w->agent, id, sizeof(id)) != 0)
+    return cst_http_send_err(c, 500, "cannot start a session");
+  wui_emit_str(w, "session", "id", id);
+  wui_emit_state(w);
+  cJSON *o = cJSON_CreateObject();
+  if (!o)
+    return cst_http_send_err(c, 500, "out of memory");
+  cJSON_AddStringToObject(o, "id", id);
+  char *json = cJSON_PrintUnformatted(o);
+  cJSON_Delete(o);
+  int rc = cst_http_send_json(c, 200, json);
+  free(json);
+  return rc;
+}
+
+static int h_session_switch(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  const cst_http_req_t *req = cst_http_request(c);
+  cJSON *j = req->body_len ? cJSON_Parse(req->body) : NULL;
+  const cJSON *id = j ? cJSON_GetObjectItem(j, "id") : NULL;
+  int rc = -2;
+  if (cJSON_IsString(id))
+    rc = cst_agent_switch_session(w->agent, id->valuestring);
+  cJSON_Delete(j);
+  if (rc != 0)
+    return cst_http_send_err(c, 404, "no such session");
+  wui_emit_state(w);
+  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
+                           "{\"ok\":true}");
+}
+
+static int h_config(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  cst_agent_config_t *cfg = cst_agent_config_mut(w->agent);
+  const cst_http_req_t *req = cst_http_request(c);
+  cJSON *j = req->body_len ? cJSON_Parse(req->body) : NULL;
+  if (!j || !cfg) {
+    cJSON_Delete(j);
+    return cst_http_send_err(c, 400, "expected a JSON object");
+  }
+  const cJSON *item;
+  if ((item = cJSON_GetObjectItem(j, "model")) && cJSON_IsString(item))
+    snprintf(cfg->model, sizeof(cfg->model), "%s", item->valuestring);
+  if ((item = cJSON_GetObjectItem(j, "provider")) && cJSON_IsString(item))
+    snprintf(cfg->provider, sizeof(cfg->provider), "%s", item->valuestring);
+  if ((item = cJSON_GetObjectItem(j, "effort")) && cJSON_IsString(item) &&
+      cst_effort_valid(item->valuestring))
+    snprintf(cfg->effort, sizeof(cfg->effort), "%s", item->valuestring);
+  if ((item = cJSON_GetObjectItem(j, "approval")) && cJSON_IsString(item)) {
+    int a = 0;
+    if (cst_approval_parse(item->valuestring, &a) == 0) {
+      cfg->approval = a;
+      cfg->auto_approve = a == CST_APPROVAL_YOLO;
+    }
+  }
+  if ((item = cJSON_GetObjectItem(j, "plan_mode")) && cJSON_IsBool(item)) {
+    cfg->plan_mode = cJSON_IsTrue(item) ? 1 : 0;
+    cfg->read_only = cfg->plan_mode;
+  }
+  cJSON_Delete(j);
+  wui_emit_state(w);
+  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
+                           "{\"ok\":true}");
+}
+
+static int h_undo(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  char report[2048] = "";
+  if (cst_agent_undo(w->agent, report, sizeof(report)) != 0)
+    return cst_http_send_err(c, 409, "nothing to undo");
+  wui_emit_str(w, "status", "message", report);
+  wui_emit_state(w);
+  return cst_http_send_str(c, 200, "text/plain; charset=utf-8", report);
+}
+
+static int h_compact(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  char err[256] = "";
+  if (cst_agent_compact(w->agent, err, sizeof(err)) != 0)
+    return cst_http_send_err(c, 500, err);
+  wui_emit_state(w);
+  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
+                           "{\"ok\":true}");
+}
+
+static int h_attach_upload(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  const cst_http_req_t *req = cst_http_request(c);
+  char name[256] = "pasted.png";
+  cst_http_query(req, "name", name, sizeof(name));
+  if (req->body_len == 0)
+    return cst_http_send_err(c, 400, "empty body");
+  char err[256] = "";
+  if (cst_agent_attach_bytes(w->agent, name, req->body, req->body_len, err,
+                             sizeof(err)) != 0)
+    return cst_http_send_err(c, 400, err[0] ? err : "cannot attach the image");
+  wui_emit_state(w);
+  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
+                           "{\"ok\":true}");
+}
+
+static int h_attach_clear(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  cst_agent_pending_clear(w->agent);
+  wui_emit_state(w);
+  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
+                           "{\"ok\":true}");
+}
+
+static int h_quit(cst_http_conn_t *c, void *ud) {
+  wui_t *w = ud;
+  w->stopping = 1;
+  return cst_http_send_str(c, 200, "application/json; charset=utf-8",
+                           "{\"ok\":true}");
+}
+
+/* --- auth ---------------------------------------------------------------- */
+
+static int token_matches(const wui_t *w, const char *given) {
+  if (!given || !w->token[0])
+    return 0;
+  size_t a = strlen(given), b = strlen(w->token);
+  if (a != b)
+    return 0;
+  unsigned diff = 0;
+  for (size_t i = 0; i < a; i++)
+    diff |= (unsigned char)given[i] ^ (unsigned char)w->token[i];
+  return diff == 0;
+}
+
+static int cookie_token(const char *cookie, char *out, size_t out_sz) {
+  const char *p = cookie;
+  while (p && *p) {
+    while (*p == ' ' || *p == ';')
+      p++;
+    if (strncmp(p, "cst_token=", 10) == 0) {
+      const char *v = p + 10;
+      const char *end = strchr(v, ';');
+      size_t n = end ? (size_t)(end - v) : strlen(v);
+      if (n >= out_sz)
+        n = out_sz - 1;
+      memcpy(out, v, n);
+      out[n] = 0;
+      return 0;
+    }
+    p = strchr(p, ';');
+  }
+  return -1;
+}
+
+/* Host header must name this machine's loopback when no token is required:
+ * a DNS-rebinding page would send its own name here. */
+static int host_is_loopback(const char *host) {
+  if (!host || !host[0])
+    return 0;
+  while (*host == ' ')
+    host++;
+  if (strncmp(host, "127.0.0.1", 9) == 0) {
+    char next = host[9];
+    return next == 0 || next == ':';
+  }
+  if (strncmp(host, "localhost", 9) == 0) {
+    char next = host[9];
+    return next == 0 || next == ':';
+  }
+  if (strncmp(host, "[::1]", 5) == 0) {
+    char next = host[5];
+    return next == 0 || next == ':';
+  }
+  return 0;
+}
+
+static int wui_auth(const cst_http_req_t *req, void *ud) {
+  wui_t *w = ud;
+  if (!w->need_auth)
+    return host_is_loopback(req->host) ? 0 : -1;
+  char buf[128];
+  if (req->authorization && strncmp(req->authorization, "Bearer ", 7) == 0 &&
+      token_matches(w, req->authorization + 7))
+    return 0;
+  if (req->cookie && cookie_token(req->cookie, buf, sizeof(buf)) == 0 &&
+      token_matches(w, buf))
+    return 0;
+  if (cst_http_query(req, "token", buf, sizeof(buf)) == 0 &&
+      token_matches(w, buf))
+    return 0;
+  return -1;
+}
+
+/* --- startup ------------------------------------------------------------- */
+
+static volatile sig_atomic_t g_webui_stop;
+
+static void webui_on_signal(int sig) {
+  (void)sig;
+  g_webui_stop = 1;
+}
+
+static void wui_make_token(char *out, size_t out_sz) {
+  unsigned char raw[16];
+  size_t got = 0;
+  FILE *fp = fopen("/dev/urandom", "rb");
+  if (fp) {
+    got = fread(raw, 1, sizeof(raw), fp);
+    fclose(fp);
+  }
+  if (got != sizeof(raw)) {
+    unsigned seed = (unsigned)(os_now_ms() * 1000.0) ^ (unsigned)os_getpid();
+    for (size_t i = 0; i < sizeof(raw); i++) {
+      seed = seed * 1103515245u + 12345u;
+      raw[i] = (unsigned char)(seed >> 16);
+    }
+  }
+  static const char hex[] = "0123456789abcdef";
+  size_t o = 0;
+  for (size_t i = 0; i < sizeof(raw) && o + 2 < out_sz; i++) {
+    out[o++] = hex[raw[i] >> 4];
+    out[o++] = hex[raw[i] & 15];
+  }
+  out[o] = 0;
+}
+
+static void open_browser(const char *url) {
+#if defined(_WIN32)
+  char cmd[600];
+  snprintf(cmd, sizeof(cmd), "start \"\" \"%s\"", url);
+  os_run_shell_c(".", cmd, 0, NULL);
+#elif defined(__APPLE__)
+  char cmd[600];
+  snprintf(cmd, sizeof(cmd), "open '%s'", url);
+  os_run_shell_c(".", cmd, 0, NULL);
+#else
+  char cmd[600];
+  snprintf(cmd, sizeof(cmd), "xdg-open '%s' >/dev/null 2>&1 &", url);
+  os_run_shell_c(".", cmd, 0, NULL);
+#endif
+  (void)url;
+}
+
+int cst_webui_run(cst_agent_t *agent, const cst_webui_opts_t *opts) {
+  cst_webui_opts_t def;
+  if (!opts) {
+    memset(&def, 0, sizeof(def));
+    opts = &def;
+  }
+  wui_t *w = calloc(1, sizeof(*w));
+  if (!w)
+    return 1;
+  pthread_mutex_init(&w->mu, NULL);
+  w->agent = agent;
+  w->perm_timeout_s = opts->perm_timeout_s;
+  w->root = opts->root;
+  pthread_cond_init(&w->cv, NULL);
+  snprintf(w->host, sizeof(w->host), "%s",
+           opts->host && opts->host[0] ? opts->host : "127.0.0.1");
+  if (opts->token && opts->token[0]) {
+    snprintf(w->token, sizeof(w->token), "%s", opts->token);
+    w->need_auth = 1;
+  } else if (strcmp(w->host, "127.0.0.1") != 0 &&
+             strcmp(w->host, "localhost") != 0 && strcmp(w->host, "::1") != 0) {
+    wui_make_token(w->token, sizeof(w->token));
+    w->need_auth = 1;
+  }
+
+  static cst_http_route_t routes[] = {
+      {"GET", "/", h_asset, NULL, 0, 0},
+      {"GET", "/api/state", h_state, NULL, 0, 0},
+      {"GET", "/api/session", h_session, NULL, 0, 0},
+      {"GET", "/api/events", h_events, NULL, 0, 0},
+      {"GET", "/api/sessions", h_sessions, NULL, 0, 0},
+      {"POST", "/api/sessions/new", h_session_new, NULL, 0, 0},
+      {"POST", "/api/sessions/switch", h_session_switch, NULL, 0, 0},
+      {"POST", "/api/turn", h_turn, NULL, 0, 0},
+      {"POST", "/api/cancel", h_cancel, NULL, 0, 0},
+      {"POST", "/api/permission", h_permission, NULL, 0, 0},
+      {"POST", "/api/ask_user", h_ask_user, NULL, 0, 0},
+      {"POST", "/api/config", h_config, NULL, 0, 0},
+      {"POST", "/api/undo", h_undo, NULL, 0, 0},
+      {"POST", "/api/compact", h_compact, NULL, 0, 0},
+      {"POST", "/api/attach", h_attach_upload, NULL, 0, 32u * 1024u * 1024u},
+      {"DELETE", "/api/attach", h_attach_clear, NULL, 0, 0},
+      {"POST", "/api/quit", h_quit, NULL, 0, 0},
+      {"GET", "*", h_asset, NULL, 0, 0},
+  };
+  for (size_t i = 0; i < sizeof(routes) / sizeof(routes[0]); i++) {
+    routes[i].ud = w;
+    routes[i].auth = w->need_auth || strcmp(routes[i].path, "/") != 0;
+  }
+  routes[0].auth = 0;  /* the shell page itself sets the cookie */
+  routes[sizeof(routes) / sizeof(routes[0]) - 1].auth = w->need_auth;
+
+  cst_http_opts_t ho;
+  memset(&ho, 0, sizeof(ho));
+  ho.host = w->host;
+  ho.port = opts->port;
+  ho.max_body = 1024 * 1024;
+  ho.max_conn = 32;
+  ho.routes = routes;
+  ho.nroutes = (int)(sizeof(routes) / sizeof(routes[0]));
+  ho.auth = wui_auth;
+  ho.auth_ud = w;
+  char err[256] = "";
+  w->srv = cst_http_start(&ho, err, sizeof(err));
+  if (!w->srv) {
+    fprintf(stderr, "webui: cannot listen on %s:%d: %s\n", w->host,
+            opts->port, err);
+    pthread_cond_destroy(&w->cv);
+    pthread_mutex_destroy(&w->mu);
+    free(w);
+    return 1;
+  }
+  char url[256];
+  snprintf(url, sizeof(url), "http://%s:%d/%s", strcmp(w->host, "0.0.0.0") == 0
+                                                   ? "127.0.0.1"
+                                                   : w->host,
+           cst_http_port(w->srv),
+           w->need_auth ? "" : "");
+  fprintf(stderr, "webui: %s\n", url);
+  if (w->need_auth)
+    fprintf(stderr, "webui: token %s  (append #token=%s to the URL)\n", w->token,
+            w->token);
+  fflush(stderr);
+  wui_emit_state(w);
+  if (opts->open_browser)
+    open_browser(url);
+
+  if (opts->prompt && opts->prompt[0]) {
+    char err2[256] = "";
+    if (wui_start_turn(w, opts->prompt, err2, sizeof(err2)) != 0)
+      fprintf(stderr, "webui: %s\n", err2);
+  }
+
+  /* Serve until Ctrl+C, /api/quit or a signal. */
+  signal(SIGINT, webui_on_signal);
+  signal(SIGTERM, webui_on_signal);
+  while (!w->stopping && !g_webui_stop) {
+    struct timespec ts;
+    ts.tv_sec = 0;
+    ts.tv_nsec = 200 * 1000 * 1000;
+    nanosleep(&ts, NULL);
+  }
+  fprintf(stderr, "webui: shutting down\n");
+  w->stopping = 1;
+  cst_http_stop(w->srv);
+  cst_http_free(w->srv);
+  for (int i = 0; i < WUI_RING; i++)
+    free(w->ring[i].frame);
+  if (w->md)
+    cst_web_md_free(w->md);
+  pthread_cond_destroy(&w->cv);
+  pthread_mutex_destroy(&w->mu);
+  free(w);
+  return 0;
+}
diff --git a/src/webui_stub.c b/src/webui_stub.c
new file mode 100644
index 0000000..dcb7041
--- /dev/null
+++ b/src/webui_stub.c
@@ -0,0 +1,15 @@
+#include "cst_agent.h"
+#include "cst_webui.h"
+
+#include <stdio.h>
+
+#ifdef CST_NO_WEBUI
+int cst_webui_run(cst_agent_t *agent, const cst_webui_opts_t *opts) {
+  (void)agent;
+  (void)opts;
+  fprintf(stderr,
+          "the WebUI was not built into this binary (CST_BUILD_WEBUI=OFF).\n"
+          "Use --headless --prompt '...' or build with make CST_WEBUI=1\n");
+  return 1;
+}
+#endif
diff --git a/tests/test_webui.c b/tests/test_webui.c
new file mode 100644
index 0000000..28f351f
--- /dev/null
+++ b/tests/test_webui.c
@@ -0,0 +1,280 @@
+/* WebUI: the socket/HTTP layer, the SSE framing, auth and the HTML
+ * sanitizer. The full turn path is covered by scripts/e2e_webui.sh, which
+ * runs a recorded stream through a real server. */
+#ifndef _DEFAULT_SOURCE
+#define _DEFAULT_SOURCE
+#endif
+
+#include "cst_http.h"
+#include "cst_net.h"
+#include "cst_util.h"
+#include "cst_web_md.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "cst_test_util.h"
+
+#define CHECK(c)                                                               \
+  do {                                                                         \
+    if (!(c)) {                                                                \
+      fprintf(stderr, "%s:%d: CHECK(%s) failed\n", __FILE__, __LINE__, #c);   \
+      exit(1);                                                                 \
+    }                                                                          \
+  } while (0)
+
+/* --- a tiny HTTP client --------------------------------------------------- */
+
+static os_socket_t connect_to(int port) {
+  char host[32];
+  snprintf(host, sizeof(host), "127.0.0.1");
+  os_socket_t s = os_net_connect(host, port, 3000);
+  CHECK(s != OS_SOCKET_BAD);
+  return s;
+}
+
+/* Sends data, reads until the peer closes (or 5 s pass). malloc'd. */
+static char *roundtrip(int port, const char *req, size_t *out_len) {
+  os_socket_t s = connect_to(port);
+  CHECK(os_net_send_all(s, req, strlen(req), 3000) == 0);
+  cst_buf_t b = {0};
+  char buf[4096];
+  for (;;) {
+    long n = os_net_recv(s, buf, sizeof(buf), 5000);
+    if (n <= 0)
+      break;
+    CHECK(cst_buf_append(&b, buf, (size_t)n) == 0);
+  }
+  os_net_close(s);
+  *out_len = b.len;
+  return cst_buf_steal(&b);
+}
+
+/* Same, but stops as soon as `needle` shows up. */
+
+/* --- handlers ------------------------------------------------------------- */
+
+static int h_hello(cst_http_conn_t *c, void *ud) {
+  (void)ud;
+  return cst_http_send_str(c, 200, "text/plain", "world");
+}
+
+static int h_secret(cst_http_conn_t *c, void *ud) {
+  (void)ud;
+  return cst_http_send_str(c, 200, "text/plain", "secret");
+}
+
+static int h_echo(cst_http_conn_t *c, void *ud) {
+  (void)ud;
+  const cst_http_req_t *r = cst_http_request(c);
+  char head[64];
+  snprintf(head, sizeof(head), "%zu:", r->body_len);
+  cst_buf_t b = {0};
+  cst_buf_puts(&b, head);
+  cst_buf_append(&b, r->body ? r->body : "", r->body_len);
+  int rc = cst_http_send(c, 200, "text/plain", b.buf, b.len);
+  cst_buf_free(&b);
+  return rc;
+}
+
+static int h_events(cst_http_conn_t *c, void *ud) {
+  (void)ud;
+  CHECK(cst_http_stream_begin(c, "text/event-stream") == 0);
+  CHECK(cst_http_stream_write(c, "event: one\ndata: {\"n\":1}\n\n", 26) == 0);
+  CHECK(cst_http_stream_write(c, "event: two\ndata: {\"n\":2}\n\n", 26) == 0);
+  CHECK(cst_http_stream_end(c) == 0);
+  return 0;
+}
+
+static int auth_bearer(const cst_http_req_t *req, void *ud) {
+  const char *want = ud;
+  if (!req->authorization)
+    return -1;
+  if (strncmp(req->authorization, "Bearer ", 7) != 0)
+    return -1;
+  return strcmp(req->authorization + 7, want) == 0 ? 0 : -1;
+}
+
+static void test_http(void) {
+  static const cst_http_route_t routes[] = {
+      {"GET", "/hello", h_hello, NULL, 0, 0},
+      {"GET", "/secret", h_secret, NULL, 1, 0},
+      {"GET", "/events", h_events, NULL, 0, 0},
+      {"POST", "/echo", h_echo, NULL, 0, 4096},
+  };
+  cst_http_opts_t o;
+  memset(&o, 0, sizeof(o));
+  o.host = "127.0.0.1";
+  o.port = 0;
+  o.max_body = 1024 * 1024;
+  o.routes = routes;
+  o.nroutes = (int)(sizeof(routes) / sizeof(routes[0]));
+  o.auth = auth_bearer;
+  o.auth_ud = (void *)"s3cret";
+  char err[256] = "";
+  cst_http_server_t *s = cst_http_start(&o, err, sizeof(err));
+  CHECK(s != NULL);
+  int port = cst_http_port(s);
+  CHECK(port > 0);
+
+  size_t n = 0;
+  char *resp = roundtrip(port, "GET /hello HTTP/1.1\r\nHost: x\r\n"
+                               "Connection: close\r\n\r\n", &n);
+  CHECK(strstr(resp, "200 OK") && strstr(resp, "world"));
+  free(resp);
+
+  /* keep-alive: two requests, one connection */
+  resp = roundtrip(port, "GET /hello HTTP/1.1\r\nHost: x\r\n\r\n"
+                         "GET /hello HTTP/1.1\r\nHost: x\r\n"
+                         "Connection: close\r\n\r\n", &n);
+  CHECK(strstr(resp, "200 OK"));
+  CHECK(strstr(resp, "200 OK") != strrchr(resp, '2')); /* twice */
+  {
+    int hits = 0;
+    for (const char *p = resp; (p = strstr(p, "200 OK")); p++)
+      hits++;
+    CHECK(hits == 2);
+  }
+  free(resp);
+
+  /* auth: without, then with the token */
+  resp = roundtrip(port, "GET /secret HTTP/1.1\r\nHost: x\r\n"
+                         "Connection: close\r\n\r\n", &n);
+  CHECK(strstr(resp, "401"));
+  free(resp);
+  resp = roundtrip(port, "GET /secret HTTP/1.1\r\nHost: x\r\n"
+                         "Authorization: Bearer s3cret\r\n"
+                         "Connection: close\r\n\r\n", &n);
+  CHECK(strstr(resp, "200") && strstr(resp, "secret"));
+  free(resp);
+
+  /* unknown route */
+  resp = roundtrip(port, "GET /nope HTTP/1.1\r\nHost: x\r\n"
+                         "Connection: close\r\n\r\n", &n);
+  CHECK(strstr(resp, "404"));
+  free(resp);
+  /* traversal is rejected before any handler runs */
+  resp = roundtrip(port, "GET /../etc/passwd HTTP/1.1\r\nHost: x\r\n"
+                         "Connection: close\r\n\r\n", &n);
+  CHECK(strstr(resp, "400") || strstr(resp, "404"));
+  free(resp);
+
+  /* a body round trip, and the per-route cap */
+  resp = roundtrip(port, "POST /echo HTTP/1.1\r\nHost: x\r\n"
+                         "Content-Length: 3\r\nConnection: close\r\n\r\nabc", &n);
+  CHECK(strstr(resp, "200") && strstr(resp, "3:abc"));
+  free(resp);
+  {
+    cst_buf_t b = {0};
+    cst_buf_puts(&b, "POST /echo HTTP/1.1\r\nHost: x\r\nContent-Length: 9999\r\n"
+                     "Connection: close\r\n\r\n");
+    for (int i = 0; i < 9999; i++)
+      cst_buf_puts(&b, "a");
+    resp = roundtrip(port, b.buf, &n);
+    CHECK(strstr(resp, "413"));
+    free(resp);
+    cst_buf_free(&b);
+  }
+
+  /* chunked streaming: the client must see the decoded frames */
+  resp = roundtrip(port, "GET /events HTTP/1.1\r\nHost: x\r\n"
+                         "Connection: close\r\n\r\n", &n);
+  CHECK(strstr(resp, "Transfer-Encoding: chunked"));
+  CHECK(strstr(resp, "event: one") && strstr(resp, "event: two"));
+  CHECK(strstr(resp, "\r\n0\r\n\r\n")); /* terminator */
+  free(resp);
+
+  cst_http_stop(s);
+  cst_http_free(s);
+}
+
+/* --- query parsing -------------------------------------------------------- */
+
+static void test_query(void) {
+  cst_http_req_t r;
+  memset(&r, 0, sizeof(r));
+  snprintf(r.query, sizeof(r.query), "token=a%%20b&since=17&x=");
+  char buf[64];
+  CHECK(cst_http_query(&r, "token", buf, sizeof(buf)) == 0);
+  CHECK(strcmp(buf, "a b") == 0);
+  CHECK(cst_http_query(&r, "since", buf, sizeof(buf)) == 0);
+  CHECK(strcmp(buf, "17") == 0);
+  CHECK(cst_http_query(&r, "nope", buf, sizeof(buf)) != 0);
+}
+
+/* --- markdown + sanitizer ------------------------------------------------- */
+
+static cst_buf_t g_md_out;
+
+static int collect_md(const char *html, size_t len, void *ud) {
+  (void)ud;
+  return cst_buf_append(&g_md_out, html, len) == 0 ? 0 : 1;
+}
+
+static void test_sanitize(void) {
+  char *html = cst_web_md_html("**hi** [x](javascript:alert(1)) "
+                               "![i](/api/attach/img-1.png)",
+                               strlen("**hi** [x](javascript:alert(1)) "
+                                      "![i](/api/attach/img-1.png)"));
+  CHECK(html != NULL);
+  CHECK(strstr(html, "<strong>hi</strong>"));
+  CHECK(strstr(html, "javascript:") == NULL);
+  CHECK(strstr(html, "/api/attach/img-1.png"));
+  free(html);
+
+  /* raw markup that sashidown would pass through gets stripped */
+  const char *evil = "<p>ok</p><script>alert(1)</script>"
+                     "<img src=\"http://evil.example/x.png\" alt=\"a\">"
+                     "<a href=\"//evil.example\">l</a>";
+  html = cst_web_md_sanitize(evil, strlen(evil));
+  CHECK(html != NULL);
+  CHECK(strstr(html, "ok"));
+  CHECK(strstr(html, "<script") == NULL);
+  CHECK(strstr(html, "evil.example/x.png") == NULL);
+  CHECK(strstr(html, "//evil.example") == NULL);
+  CHECK(strstr(html, "<a") == NULL); /* an unusable href drops the tag */
+  free(html);
+
+  /* streaming: a javascript: link is dropped, a split tag never leaks */
+  {
+    cst_buf_free(&g_md_out);
+    const char *src = "see [x](javascript:alert(1)) and **ok**";
+    cst_web_md_t *md = cst_web_md_new(collect_md, NULL);
+    CHECK(md != NULL);
+    CHECK(cst_web_md_feed(md, src, 4) == 0); /* a deliberately split tag */
+    CHECK(cst_web_md_feed(md, src + 4, strlen(src) - 4) == 0);
+    CHECK(cst_web_md_finish(md) == 0);
+    cst_web_md_free(md);
+    const char *out = g_md_out.buf ? g_md_out.buf : "";
+    CHECK(strstr(out, "javascript:") == NULL);
+    CHECK(strstr(out, "href") == NULL);
+    CHECK(strstr(out, "see"));
+    CHECK(strstr(out, "<strong>ok</strong>") != NULL);
+    cst_buf_free(&g_md_out);
+  }
+  {
+    /* and the same text fed one byte at a time still comes out whole */
+    cst_buf_free(&g_md_out);
+    const char *md_src = "**bold** and [ok](https://example.com)";
+    cst_web_md_t *md = cst_web_md_new(collect_md, NULL);
+    CHECK(md != NULL);
+    for (size_t i = 0; i < strlen(md_src); i++)
+      CHECK(cst_web_md_feed(md, md_src + i, 1) == 0);
+    CHECK(cst_web_md_finish(md) == 0);
+    cst_web_md_free(md);
+    CHECK(strstr(g_md_out.buf, "<strong>bold</strong>"));
+    CHECK(strstr(g_md_out.buf, "https://example.com"));
+    CHECK(strstr(g_md_out.buf, "noopener") != NULL);
+    cst_buf_free(&g_md_out);
+  }
+}
+
+int main(void) {
+  CHECK(os_net_init() == 0);
+  test_query();
+  test_sanitize();
+  test_http();
+  printf("test_webui: OK\n");
+  return 0;
+}
diff --git a/web/app.js b/web/app.js
new file mode 100644
index 0000000..0c50f9c
--- /dev/null
+++ b/web/app.js
@@ -0,0 +1,433 @@
+/* CST-Agent WebUI client: HTTP + SSE against the engine in the same binary.
+ * No build step, no dependencies: the server renders Markdown, this file
+ * only moves messages around and draws them. */
+'use strict';
+
+/* --- token: from ?token= / #token= once, then kept in a cookie by the
+ * server; the query parameter is appended to every request so EventSource
+ * (which cannot set headers) works as well. --- */
+const TOKEN = (() => {
+  const q = new URLSearchParams(location.search);
+  if (q.get('token')) return q.get('token');
+  const h = location.hash.replace(/^#/, '');
+  const hp = new URLSearchParams(h);
+  return hp.get('token') || '';
+})();
+
+function api(path, opt) {
+  if (TOKEN) path += (path.includes('?') ? '&' : '?') + 'token=' + encodeURIComponent(TOKEN);
+  return fetch(path, opt);
+}
+async function getJSON(path) {
+  const r = await api(path);
+  if (!r.ok) throw new Error((await r.text()) || r.statusText);
+  return r.json();
+}
+async function post(path, body) {
+  const r = await api(path, {
+    method: 'POST',
+    headers: body === undefined ? {} : { 'Content-Type': 'application/json' },
+    body: body === undefined ? undefined : JSON.stringify(body),
+  });
+  const text = await r.text();
+  if (!r.ok) throw new Error(text || r.statusText);
+  return text ? JSON.parse(text) : {};
+}
+
+const $ = (id) => document.getElementById(id);
+const log = $('log');
+let state = {};
+let live = null;      /* {body, html, think} for the streaming assistant block */
+let tools = new Map();/* tool call id -> element */
+let permReq = null;   /* pending permission event */
+let askReq = null;    /* pending question */
+let firstPaint = true;
+
+/* --- transcript ---------------------------------------------------------- */
+
+function atBottom() {
+  return log.scrollTop + log.clientHeight >= log.scrollHeight - 40;
+}
+function scrollDown(force) {
+  if (force || atBottom()) log.scrollTop = log.scrollHeight;
+}
+function el(tag, cls, text) {
+  const e = document.createElement(tag);
+  if (cls) e.className = cls;
+  if (text !== undefined) e.textContent = text;
+  return e;
+}
+function bubble(who, cls) {
+  const m = el('div', 'msg ' + (cls || ''));
+  m.appendChild(el('div', 'who', who));
+  const b = el('div', 'body');
+  m.appendChild(b);
+  log.appendChild(m);
+  scrollDown(true);
+  return { root: m, body: b };
+}
+
+function renderMessage(m) {
+  if (m.role === 'system') return;
+  if (m.role === 'tool') return; /* drawn with its call */
+  const cls = m.role === 'user' ? 'user' : 'assistant';
+  const who = m.role === 'user' ? 'You' : 'Assistant';
+  const b = bubble(who, cls);
+  if (m.role === 'assistant' && m.html) b.body.innerHTML = m.html;
+  else b.body.textContent = m.content || '';
+  if (m.reasoning) {
+    const d = el('details', 'think');
+    d.appendChild(el('summary', null, 'Thought'));
+    d.appendChild(el('div', null, m.reasoning));
+    b.root.insertBefore(d, b.body);
+  }
+  if (m.attach) {
+    for (const a of m.attach) {
+      const img = el('img');
+      img.alt = a.name || 'image';
+      img.src = 'api/attach/' + a.rel + (TOKEN ? '?token=' + encodeURIComponent(TOKEN) : '');
+      log.insertBefore(img, null);
+    }
+  }
+}
+
+async function loadSession() {
+  const data = await getJSON('api/session');
+  log.textContent = '';
+  firstPaint = true;
+  for (const m of data.messages) renderMessage(m);
+  firstPaint = false;
+  scrollDown(true);
+}
+
+/* --- live blocks --------------------------------------------------------- */
+
+function ensureLive() {
+  if (live) return live;
+  const b = bubble('Assistant', 'assistant');
+  live = { root: b.root, body: b.body, html: '', think: null };
+  return live;
+}
+
+function thinkBlock(text) {
+  const l = ensureLive();
+  if (!l.think) {
+    const d = el('details', 'think');
+    d.appendChild(el('summary', null, 'Thought'));
+    const t = el('div');
+    d.appendChild(t);
+    l.root.insertBefore(d, l.body);
+    l.think = t;
+  }
+  l.think.textContent += text;
+  return l;
+}
+
+function toolCard(ev) {
+  let c = tools.get(ev.id);
+  if (!c) {
+    const d = el('details', 'tool');
+    const s = el('summary', null, ev.name || 'tool');
+    d.appendChild(s);
+    const args = el('div', 'args', JSON.stringify(ev.args || {}, null, 0));
+    d.appendChild(args);
+    const out = el('pre');
+    d.appendChild(out);
+    log.appendChild(d);
+    c = { root: d, sum: s, out, open: false };
+    tools.set(ev.id, c);
+  }
+  return c;
+}
+
+function onTool(ev) {
+  const c = toolCard(ev);
+  if (ev.phase === 'start' || ev.phase === 'begin') {
+    c.sum.classList.add('spin');
+    c.open = true;
+    c.root.open = true;
+  } else if (ev.phase === 'end' || ev.phase === 'done') {
+    c.sum.classList.remove('spin');
+  }
+  if (ev.detail && !c.out.textContent) c.out.textContent = ev.detail;
+  scrollDown(false);
+}
+
+function onToolResult(ev) {
+  const c = toolCard(ev);
+  c.sum.classList.remove('spin');
+  c.out.textContent = (ev.out || '') + (ev.truncated ? '\n… (截断)' : '');
+  if (ev.exit) {
+    c.sum.appendChild(el('span', ev.exit > 0 ? 'exit-bad' : '', ' exit=' + ev.exit));
+  }
+  scrollDown(false);
+}
+
+/* --- state / status ------------------------------------------------------ */
+
+function applyState(s) {
+  state = s;
+  $('ws').textContent = s.workspace || '';
+  $('ws').title = s.workspace || '';
+  $('model').textContent = (s.provider ? s.provider + ':' : '') + (s.model || '-');
+  const pm = $('planmode');
+  pm.textContent = s.plan_mode ? 'Plan' : 'Build';
+  pm.classList.toggle('on', !!s.plan_mode);
+  $('approval').textContent = s.approval || 'auto';
+  $('ctx').textContent = s.context_tokens ? (s.context_tokens + ' tok') : '';
+  const u = s.usage || {};
+  $('usage').textContent = u.requests
+    ? `${u.requests} req · ${u.prompt_tokens}/${u.completion_tokens} tok` +
+      (u.priced && u.cost ? ` · ${u.currency}${u.cost.toFixed(4)}` : '')
+    : '';
+  const busy = !!s.status_busy;
+  $('btn-stop').hidden = !busy;
+  $('btn-send').hidden = busy;
+  $('status').textContent = busy ? '运行中…' : '就绪';
+  const p = $('pending');
+  p.hidden = !(s.pending_images && s.pending_images.length);
+  p.textContent = (s.pending_images || []).join('  ');
+  const t = $('todo');
+  t.hidden = !s.todo;
+  if (s.todo) {
+    t.textContent = '';
+    t.appendChild(el('h4', null, '任务'));
+    t.appendChild(el('div', null, s.todo));
+  }
+}
+
+/* --- SSE ----------------------------------------------------------------- */
+
+function connect() {
+  const url = 'api/events' + (TOKEN ? '?token=' + encodeURIComponent(TOKEN) : '');
+  const es = new EventSource(url);
+  es.addEventListener('state', (e) => applyState(JSON.parse(e.data)));
+  es.addEventListener('status', (e) => { $('status').textContent = JSON.parse(e.data).message; });
+  es.addEventListener('assistant_html', (e) => {
+    const l = ensureLive();
+    l.html += JSON.parse(e.data).text;
+    l.body.innerHTML = l.html;
+    scrollDown(false);
+  });
+  es.addEventListener('assistant_delta', () => {});
+  es.addEventListener('think_delta', (e) => {
+    thinkBlock(JSON.parse(e.data).text);
+    scrollDown(false);
+  });
+  es.addEventListener('tool', (e) => onTool(JSON.parse(e.data)));
+  es.addEventListener('tool_result', (e) => onToolResult(JSON.parse(e.data)));
+  es.addEventListener('todo', (e) => applyState(Object.assign({}, state, { todo: JSON.parse(e.data).text })));
+  es.addEventListener('session', () => loadSession());
+  es.addEventListener('permission', (e) => showPermission(JSON.parse(e.data)));
+  es.addEventListener('permission_done', () => closeModal());
+  es.addEventListener('ask_user', (e) => showAsk(JSON.parse(e.data)));
+  es.addEventListener('turn_end', (e) => {
+    const d = JSON.parse(e.data);
+    live = null;
+    if (d.rc) bubble('Error', 'assistant').body.textContent = d.error || ('rc=' + d.rc);
+    else loadSession(); /* replace the live view with the stored messages */
+  });
+  es.onerror = () => { $('status').textContent = '连接中断，重连中…'; };
+}
+
+/* --- modals -------------------------------------------------------------- */
+
+function openModal(node) {
+  const box = $('modal-box');
+  box.textContent = '';
+  box.appendChild(node);
+  $('modal').hidden = false;
+}
+function closeModal() {
+  $('modal').hidden = true;
+  $('modal-box').textContent = '';
+  permReq = askReq = null;
+}
+window.addEventListener('keydown', (e) => {
+  if (e.key === 'Escape' && !$('modal').hidden) closeModal();
+});
+
+function showPermission(ev) {
+  permReq = ev;
+  const box = document.createDocumentFragment();
+  box.appendChild(el('h3', null, (ev.sandbox ? '沙箱拦截：要在沙箱外重跑？' : '允许 ' + ev.tool + '？')));
+  if (ev.preview) {
+    const pre = el('pre');
+    pre.textContent = ev.preview;
+    box.appendChild(pre);
+  } else if (ev.detail) {
+    const pre = el('pre');
+    pre.textContent = ev.detail;
+    box.appendChild(pre);
+  }
+  const row = el('div', 'buttons');
+  const answer = (n) => { post('api/permission', { id: ev.id, answer: n }).catch(() => {}); closeModal(); };
+  row.appendChild(Object.assign(el('button', 'danger', '拒绝'), { onclick: () => answer(0) }));
+  row.appendChild(Object.assign(el('button', 'ok', '允许一次'), { onclick: () => answer(1) }));
+  row.appendChild(Object.assign(el('button', null, '总是允许（工具）'), { onclick: () => answer(2) }));
+  if (ev.tool === 'run_shell')
+    row.appendChild(Object.assign(el('button', null, '总是允许（该前缀）'), { onclick: () => answer(3) }));
+  box.appendChild(row);
+  openModal(box);
+}
+
+function showAsk(ev) {
+  askReq = ev;
+  const box = document.createDocumentFragment();
+  box.appendChild(el('h3', null, 'Agent 提问'));
+  const pre = el('pre');
+  pre.textContent = ev.question || '';
+  box.appendChild(pre);
+  const row = el('div', 'buttons');
+  const send = (text, dismiss) => {
+    post('api/ask_user', { id: ev.id, text, dismiss: !!dismiss }).catch(() => {});
+    closeModal();
+  };
+  for (const opt of ev.options || []) {
+    row.appendChild(Object.assign(el('button', null, opt), { onclick: () => send(opt, false) }));
+  }
+  const free = el('input');
+  free.placeholder = '自定义回答';
+  free.style.cssText = 'flex:1;min-width:220px;background:var(--bg);color:var(--fg);border:1px solid var(--line);border-radius:6px;padding:5px 8px;font:inherit';
+  row.appendChild(free);
+  row.appendChild(Object.assign(el('button', 'ok', '回答'), { onclick: () => send(free.value, false) }));
+  row.appendChild(Object.assign(el('button', 'danger', '忽略'), { onclick: () => send('', true) }));
+  box.appendChild(row);
+  openModal(box);
+  setTimeout(() => free.focus(), 0);
+}
+
+async function showSessions() {
+  const data = await getJSON('api/sessions');
+  const box = document.createDocumentFragment();
+  box.appendChild(el('h3', null, '会话'));
+  for (const s of data.sessions) {
+    const row = el('div', 'sess');
+    row.appendChild(el('span', 'id', (s.id === data.current ? '* ' : '  ') + s.id.slice(0, 12)));
+    row.appendChild(el('span', 't', s.title || '(空)'));
+    row.appendChild(el('span', 'id', s.messages + ' msgs'));
+    row.appendChild(Object.assign(el('button', null, '打开'), {
+      onclick: async () => {
+        await post('api/sessions/switch', { id: s.id });
+        closeModal();
+        await loadSession();
+      },
+    }));
+    box.appendChild(row);
+  }
+  const row = el('div', 'buttons');
+  row.appendChild(Object.assign(el('button', 'ok', '新建会话'), {
+    onclick: async () => { await post('api/sessions/new', {}); closeModal(); await loadSession(); },
+  }));
+  row.appendChild(Object.assign(el('button', null, '关闭'), { onclick: closeModal }));
+  box.appendChild(row);
+  openModal(box);
+}
+
+function showModel() {
+  const box = document.createDocumentFragment();
+  box.appendChild(el('h3', null, '模型与模式'));
+  const mk = (label, value, apply) => {
+    const row = el('div', 'buttons');
+    row.appendChild(el('span', 'muted', label));
+    const input = el('input');
+    input.value = value || '';
+    input.style.cssText = 'flex:1;min-width:200px;background:var(--bg);color:var(--fg);border:1px solid var(--line);border-radius:6px;padding:5px 8px;font:inherit';
+    row.appendChild(input);
+    row.appendChild(Object.assign(el('button', 'ok', '应用'), {
+      onclick: async () => { await post('api/config', apply(input.value)); },
+    }));
+    box.appendChild(row);
+  };
+  mk('模型', state.model, (v) => ({ model: v }));
+  mk('provider', state.provider, (v) => ({ provider: v }));
+  const row = el('div', 'buttons');
+  row.appendChild(el('span', 'muted', '推理强度'));
+  for (const level of ['low', 'medium', 'high', 'max']) {
+    row.appendChild(Object.assign(el('button', level === state.effort ? 'ok' : '', level), {
+      onclick: () => post('api/config', { effort: level }),
+    }));
+  }
+  box.appendChild(row);
+  const row2 = el('div', 'buttons');
+  row2.appendChild(el('span', 'muted', '审批'));
+  for (const mode of ['ask', 'auto', 'yolo']) {
+    row2.appendChild(Object.assign(el('button', mode === state.approval ? 'ok' : '', mode), {
+      onclick: () => post('api/config', { approval: mode }),
+    }));
+  }
+  row2.appendChild(Object.assign(el('button', state.plan_mode ? 'ok' : '', state.plan_mode ? 'Plan' : 'Build'), {
+    onclick: () => post('api/config', { plan_mode: !state.plan_mode }),
+  }));
+  box.appendChild(row2);
+  const row3 = el('div', 'buttons');
+  row3.appendChild(Object.assign(el('button', null, '关闭'), { onclick: closeModal }));
+  box.appendChild(row3);
+  openModal(box);
+}
+
+/* --- composer ------------------------------------------------------------ */
+
+async function send() {
+  const input = $('input');
+  const text = input.value.trim();
+  if (!text || state.status_busy) return;
+  input.value = '';
+  bubble('You', 'user').body.textContent = text;
+  try {
+    await post('api/turn', { text });
+  } catch (e) {
+    bubble('Error', 'assistant').body.textContent = String(e.message || e);
+  }
+}
+
+$('btn-send').onclick = send;
+$('btn-stop').onclick = () => post('api/cancel', {}).catch(() => {});
+$('btn-sessions').onclick = () => showSessions().catch((e) => alert(e.message));
+$('btn-model').onclick = showModel;
+$('btn-undo').onclick = () => post('api/undo', {}).catch((e) => alert(e.message));
+$('btn-compact').onclick = () => post('api/compact', {}).catch((e) => alert(e.message));
+$('btn-clear').onclick = () => { log.textContent = ''; };
+$('input').addEventListener('keydown', (e) => {
+  if (e.key === 'Enter' && !e.shiftKey && !e.isComposing) {
+    e.preventDefault();
+    send();
+  }
+});
+$('input').addEventListener('input', (e) => {
+  e.target.style.height = 'auto';
+  e.target.style.height = Math.min(e.target.scrollHeight, 240) + 'px';
+});
+
+async function upload(file) {
+  const r = await api('api/attach?name=' + encodeURIComponent(file.name), {
+    method: 'POST',
+    headers: { 'Content-Type': file.type || 'application/octet-stream' },
+    body: file,
+  });
+  if (!r.ok) alert(await r.text());
+}
+$('file').addEventListener('change', async (e) => {
+  for (const f of e.target.files) await upload(f);
+  e.target.value = '';
+});
+document.addEventListener('paste', async (e) => {
+  for (const item of e.clipboardData.items) {
+    if (item.kind === 'file' && item.type.startsWith('image/')) {
+      e.preventDefault();
+      await upload(item.getAsFile());
+    }
+  }
+});
+document.addEventListener('dragover', (e) => e.preventDefault());
+document.addEventListener('drop', async (e) => {
+  if (!e.dataTransfer.files.length) return;
+  e.preventDefault();
+  for (const f of e.dataTransfer.files) await upload(f);
+});
+
+/* --- go ------------------------------------------------------------------ */
+
+connect();
+loadSession().catch(() => {});
+getJSON('api/state').then(applyState).catch(() => {});
diff --git a/web/index.html b/web/index.html
new file mode 100644
index 0000000..24b74ca
--- /dev/null
+++ b/web/index.html
@@ -0,0 +1,41 @@
+<!DOCTYPE html>
+<html lang="zh-CN">
+<head>
+<meta charset="utf-8">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<title>CST-Agent</title>
+<link rel="stylesheet" href="style.css">
+</head>
+<body>
+<header id="bar">
+  <span class="tag" id="planmode">Build</span>
+  <span class="tag" id="approval">auto</span>
+  <span class="ws" id="ws" title="workspace"></span>
+  <span class="model" id="model" title="model">-</span>
+  <span class="muted" id="ctx"></span>
+  <span class="grow"></span>
+  <button id="btn-sessions" title="sessions">会话</button>
+  <button id="btn-model" title="model">模型</button>
+  <button id="btn-undo" title="undo">撤销</button>
+  <button id="btn-compact" title="compact">压缩</button>
+  <button id="btn-clear" title="clear view">清屏</button>
+</header>
+
+<main id="log"></main>
+<aside id="todo" hidden></aside>
+
+<footer id="composer">
+  <div id="pending" hidden></div>
+  <div class="row">
+    <textarea id="input" rows="1" placeholder="输入消息，Enter 发送，Shift+Enter 换行"></textarea>
+    <button id="btn-send">发送</button>
+    <button id="btn-stop" hidden>停止</button>
+    <label class="att" title="附上图片"><input type="file" id="file" accept="image/*" hidden>+图</label>
+  </div>
+  <div class="hint"><span id="status">就绪</span><span class="grow"></span><span id="usage" class="muted"></span></div>
+</footer>
+
+<div id="modal" hidden><div id="modal-box"></div></div>
+<script src="app.js"></script>
+</body>
+</html>
diff --git a/web/style.css b/web/style.css
new file mode 100644
index 0000000..40c79f0
--- /dev/null
+++ b/web/style.css
@@ -0,0 +1,103 @@
+:root {
+  --bg: #14161a;
+  --bg2: #1b1e24;
+  --fg: #d8dde5;
+  --muted: #8b93a1;
+  --line: #2a2f38;
+  --accent: #7fb2ff;
+  --ok: #7ddc8f;
+  --warn: #ffcc66;
+  --err: #ff7b72;
+  --tool: #b5e3c8;
+}
+* { box-sizing: border-box; }
+html, body { margin: 0; height: 100%; }
+body {
+  background: var(--bg); color: var(--fg);
+  font: 14px/1.55 ui-monospace, SFMono-Regular, Menlo, Consolas, "Noto Sans Mono CJK SC", monospace;
+  display: flex; flex-direction: column; height: 100%;
+}
+button {
+  background: var(--bg2); color: var(--fg); border: 1px solid var(--line);
+  border-radius: 6px; padding: 3px 9px; font: inherit; cursor: pointer;
+}
+button:hover { border-color: var(--accent); }
+.grow { flex: 1; }
+.muted { color: var(--muted); }
+
+#bar {
+  display: flex; align-items: center; gap: 8px; padding: 6px 10px;
+  border-bottom: 1px solid var(--line); background: var(--bg2);
+  position: sticky; top: 0; z-index: 3; flex-wrap: wrap;
+}
+.tag { border: 1px solid var(--line); border-radius: 999px; padding: 0 8px; color: var(--muted); }
+.tag.on { color: var(--bg); background: var(--accent); border-color: var(--accent); }
+.ws { color: var(--muted); overflow: hidden; text-overflow: ellipsis; max-width: 40vw; white-space: nowrap; }
+.model { color: var(--accent); }
+
+#log { flex: 1; overflow: auto; padding: 12px 14px 20px; }
+#log .msg { margin: 0 0 14px; }
+#log .who { color: var(--muted); font-size: 12px; margin-bottom: 2px; }
+#log .body { white-space: pre-wrap; word-break: break-word; }
+#log .assistant .body > :first-child { margin-top: 0; }
+#log .body pre {
+  background: var(--bg2); border: 1px solid var(--line); border-radius: 6px;
+  padding: 8px 10px; overflow: auto;
+}
+#log .body code { background: var(--bg2); border-radius: 4px; padding: 0 3px; }
+#log .body pre code { background: none; padding: 0; }
+#log .body table { border-collapse: collapse; }
+#log .body th, #log .body td { border: 1px solid var(--line); padding: 2px 6px; }
+#log .body blockquote { border-left: 3px solid var(--line); margin: 0; padding-left: 10px; color: var(--muted); }
+#log .body a { color: var(--accent); }
+#log .body img { max-width: min(420px, 100%); border-radius: 6px; border: 1px solid var(--line); }
+
+details.think { color: var(--muted); margin: 4px 0; }
+details.think summary { cursor: pointer; }
+details.tool {
+  border: 1px solid var(--line); border-radius: 6px; margin: 6px 0; background: var(--bg2);
+}
+details.tool > summary { cursor: pointer; padding: 4px 8px; color: var(--tool); }
+details.tool .args, details.tool pre { margin: 0; padding: 6px 10px; white-space: pre-wrap; }
+details.tool pre { border-top: 1px solid var(--line); max-height: 40vh; overflow: auto; }
+.tool .exit-bad { color: var(--err); }
+.spin::after { content: " …"; color: var(--warn); }
+
+#todo {
+  border-top: 1px solid var(--line); background: var(--bg2); padding: 6px 12px;
+  max-height: 22vh; overflow: auto; white-space: pre-wrap; font-size: 13px;
+}
+#todo h4 { margin: 0 0 4px; color: var(--muted); font-size: 12px; font-weight: normal; }
+
+#composer { border-top: 1px solid var(--line); background: var(--bg2); padding: 8px 10px; }
+#composer .row { display: flex; gap: 8px; align-items: flex-end; }
+#input {
+  flex: 1; resize: vertical; min-height: 34px; max-height: 40vh;
+  background: var(--bg); color: var(--fg); border: 1px solid var(--line);
+  border-radius: 6px; padding: 7px 9px; font: inherit;
+}
+.att {
+  border: 1px solid var(--line); border-radius: 6px; padding: 5px 9px; cursor: pointer;
+}
+.hint { display: flex; gap: 10px; font-size: 12px; color: var(--muted); padding-top: 4px; }
+#pending { color: var(--warn); font-size: 12px; padding-bottom: 4px; }
+
+#modal {
+  position: fixed; inset: 0; background: rgba(0, 0, 0, .55);
+  display: flex; align-items: center; justify-content: center; z-index: 9;
+}
+#modal-box {
+  background: var(--bg2); border: 1px solid var(--line); border-radius: 10px;
+  padding: 14px; width: min(820px, 94vw); max-height: 88vh; overflow: auto;
+}
+#modal-box h3 { margin: 0 0 8px; }
+#modal-box pre {
+  background: var(--bg); border: 1px solid var(--line); border-radius: 6px;
+  padding: 8px; max-height: 46vh; overflow: auto; white-space: pre-wrap;
+}
+#modal-box .buttons { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 10px; }
+#modal-box .danger { border-color: var(--err); color: var(--err); }
+#modal-box .ok { border-color: var(--ok); color: var(--ok); }
+.sess { display: flex; gap: 8px; align-items: center; padding: 4px 0; border-bottom: 1px solid var(--line); }
+.sess .id { color: var(--muted); font-size: 12px; }
+.sess .t { flex: 1; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }