Usability pass: tool registry, TUI polish, saved keys and settings

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.

fixtures/test_fix_test/Makefile

@@ -0,0 +1,14 @@
+CC ?= cc
+CFLAGS ?= -std=c11 -Wall -Wextra -O2
+
+.PHONY: test clean
+
+test_strutil: strutil.c strutil.h tests/test_strutil.c
+	$(CC) $(CFLAGS) -o $@ strutil.c tests/test_strutil.c
+
+test: test_strutil
+	@echo run >> .test_runs
+	./test_strutil
+
+clean:
+	rm -f test_strutil

fixtures/test_fix_test/TASK.md

@@ -0,0 +1,6 @@
+# 任务：先跑测试，再修，再跑测试
+
+1. 先运行 `make test`，看哪些用例失败（此时不要改代码）。
+2. 阅读 `strutil.c`，修复导致失败的 bug（不要修改 `tests/` 下的文件）。
+3. 再次运行 `make test`，确认全部通过。
+4. 用简短中文说明你修了什么。

fixtures/test_fix_test/check.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+# Pass iff tests pass now AND the agent really ran `make test` at least twice
+# (before and after the fix; an over-eager duplicate filter would skip one).
+set -euo pipefail
+cd "$(dirname "$0")"
+runs=$(wc -l < .test_runs 2>/dev/null || echo 0)
+echo "agent test runs: $runs"
+git_clean_tests=1
+grep -q 'check_vowels("Queue", 4);' tests/test_strutil.c || git_clean_tests=0
+[ "$git_clean_tests" = 1 ] || { echo "tests were modified"; exit 1; }
+[ "$runs" -ge 2 ] || { echo "make test ran fewer than 2 times"; exit 1; }
+make test

fixtures/test_fix_test/strutil.c

@@ -0,0 +1,23 @@
+#include "strutil.h"
+
+#include <ctype.h>
+#include <string.h>
+
+void str_reverse(char *s) {
+  size_t n = strlen(s);
+  for (size_t i = 0; i < n / 2; i++) {
+    char t = s[i];
+    s[i] = s[n - i];
+    s[n - i] = t;
+  }
+}
+
+int count_vowels(const char *s) {
+  int k = 0;
+  for (; *s; s++) {
+    char c = (char)tolower((unsigned char)*s);
+    if (c == 'a' || c == 'e' || c == 'i' || c == 'o')
+      k++;
+  }
+  return k;
+}

fixtures/test_fix_test/strutil.h

@@ -0,0 +1,7 @@
+#ifndef STRUTIL_H
+#define STRUTIL_H
+
+void str_reverse(char *s);
+int count_vowels(const char *s);
+
+#endif

fixtures/test_fix_test/tests/test_strutil.c

@@ -0,0 +1,39 @@
+#include "../strutil.h"
+
+#include <stdio.h>
+#include <string.h>
+
+static int fails;
+
+static void check_rev(const char *in, const char *want) {
+  char buf[64];
+  snprintf(buf, sizeof(buf), "%s", in);
+  str_reverse(buf);
+  if (strcmp(buf, want) != 0) {
+    printf("FAIL str_reverse(\"%s\") = \"%s\", want \"%s\"\n", in, buf, want);
+    fails++;
+  }
+}
+
+static void check_vowels(const char *in, int want) {
+  int got = count_vowels(in);
+  if (got != want) {
+    printf("FAIL count_vowels(\"%s\") = %d, want %d\n", in, got, want);
+    fails++;
+  }
+}
+
+int main(void) {
+  check_rev("abc", "cba");
+  check_rev("ab", "ba");
+  check_rev("", "");
+  check_vowels("education", 5);
+  check_vowels("RHYTHM", 0);
+  check_vowels("Queue", 4);
+  if (fails) {
+    printf("%d test(s) failed\n", fails);
+    return 1;
+  }
+  printf("all tests passed\n");
+  return 0;
+}