Sessions: rename, delete and search; /api/retry regenerates the last
answer, editing a prompt resends from there; /api/export downloads the
transcript as Markdown (cst_session_export_md). Session messages carry
note/tool_result markers, so a reload rebuilds the tool steps with
their arguments, output and exit status; subagent progress is shown.
Diff and settings: /api/diff shows the real diff; /api/settings covers
protocol, max_steps, tool switches and confirm; /api/permissions edits
the rules; sandbox status is reported. Session rename no longer reads
past a short title.
Commands: slash commands with completion in the composer (/model,
/provider, /new, /retry, /undo, /compact, /export, /diff, /init,
/skill and more), a Ctrl+P palette, Shift+Tab cycles the approval
mode, F1 or ? shows the keys. "Thinking expanded" is saved in the
settings (show_thinking), "expand all tool output" in the browser.
Extensions: GET /api/extensions lists MCP servers, plugins, skills,
agent roles and subagent runs; POST /api/extensions/reload and
/api/extensions/trust; a workspace switch reloads them. /api/init and
/api/skill run on the server (cst_init_prompt shared with the TUI).
Errors, statuses and [cst] notes are shown in Chinese with a readable
reason instead of rc=; a failed turn's error survives the reload.
Tests: scripts/e2e_webui_sessions.py, e2e_webui_workspace.py and
e2e_webui_ext.py, run from e2e_webui.sh.
The front end is rebuilt on the design tokens the desktop app ships (surfaces,
color-mix borders, alpha hovers, accent): a 30-icon inline SVG sprite, dark and
light themes, layout switches as deep links (?side=0, ?panel=0, ?theme=light)
resolved before the first paint. The empty page is one line and leaves with the
first turn; the right rail keeps three cards - todo, file changes (+N -M) and
context (tokens, prompt cache hit rate). Both rails animate in and out, and a
collapsed rail widens its grid track to 0 instead of being removed, so the
transcript never slides into a zero-width column.
- src/webui.c: POST /api/workspace - re-root the agent at another directory
(permission rules, metrics, AGENTS.md follow) and start a session there, as
sessions live per directory; state also reports cached/cache_miss tokens
- src/agent_loop.c: cst_agent_set_workspace(), rebuilt prompt and re-measured
budget; the auto-compact threshold is 75% of the window (was 60%)
- src/tui.c: /web forks a WebUI next to the TUI - separate process and a new
session, because cst_webui_run() blocks and two writers corrupt one session
- src/os_compat.c, src/os_win.c: run_shell runs without a time limit unless
CST_SHELL_TIMEOUT asks for one, so builds and long clones finish
- src/main.c, include/cst_webui.h: one CST_WEBUI_DEFAULT_PORT for --help, the
docs and /web; Termux opens the browser through termux-open-url
- README.md, docs/webui.md, docs/env_openai.md: /web, /api/workspace, the new
state fields, the 75% threshold and the layout deep links
tests/e2e_webui.sh green (permission round-trip, token paths, --web-dev);
make check green.
Images
- vision gate: text-only models get a note instead of image parts and no
view_image tool; unknown models retry once without images on HTTP 400
- paste: Ctrl+V and /attach paste read the clipboard (wl-paste, xclip,
pngpaste/osascript, Win32 PNG or CF_DIB converted to PNG); pasting image
file paths attaches them
- MCP image content is stored in the session and sent with the tool result
- attach: rel path validation, base64 decode, /retry keeps images
Model registry
- built-in src/models_builtin.json embedded at build time, merged with
<config>/models.json and cached GET /models metadata (context, vision,
pricing); most specific rule wins per field
- /model labels, /status source, --list-models [provider]
Cache and cost
- stable request prefix (frozen tools, notes as messages), DeepSeek prefix
completion, OpenAI/Anthropic cache hints, /cost and hit rate in the status
Tools
- Table-driven tool registry with permission classes and default/minimal
profiles; new tools: edit_file, list_dir, glob, grep, delete_file,
move_file, todo_write, web_fetch, ask_user (plus read_file paging).
- Built-in Myers diff; write tools return unified diffs.
- Persistent permission rules (.agent/permissions.json), per-turn undo
snapshots (.agent/undo), AGENTS.md project notes, auto-compact at 80%
of the model context, cancellable run_shell with process-group kill.
TUI
- Table-driven slash commands: /provider /key /effort /status /tools
/permissions /yolo /undo /retry /diff /export /copy /rename /delete
/init /max-steps /todo, with / and @ completion.
- Permission modal with diff and prefix rules, ask_user modal, todo
panel, header with model/effort/context, bracketed paste, line editing,
wide-char cursor, NO_COLOR and ASCII fallback; Esc never quits.
Startup and configuration
- API keys are entered in the TUI (hidden) and saved per provider in
<config>/credentials (0600); env variables are only a fallback.
- Last provider, per-provider model and reasoning effort are remembered
in <config>/settings.json; --effort/-e and /effort send
reasoning_effort (low|medium|high|max) to models that accept it.
- DeepSeek preset uses deepseek-flash / deepseek-v4-pro.
- Session flags --new/--continue/--resume/--list-sessions, --yolo,
--confirm.
Compatibility and tests
- ncurses detection, macOS/Homebrew support, make install, XDG config
dir, POSIX cleanups; Gitea CI (gcc/clang/asan/musl/macOS).
- Unit tests for diff, fs tools, registry, undo/perms and config;
e2e fixtures multi_file_refactor and ask_or_todo; vendored cJSON.
WHC