chore: gate complexity only on functions touched by the change

Whole-tree radon blocking let 16 legacy C+ functions block every commit,
including docs-only ones. Touched functions still block; legacy debt is
reported as a warning.

.claude/scripts/hooks/pre-commit-guard.sh

@@ -41,10 +41,35 @@ for CODE_DIR in "${CODE_DIRS[@]}"; do
         fi
     fi
 
+    # 复杂度只对"本次改动触及的函数"硬拦: 全量拦截会让存量债务挡住一切提交
+    # (含纯文档提交),久之只剩绕过一条路;存量 ≥C 函数降为告警,随触及随还。
+    # 用 HEAD 对比工作区+暂存区: 钩子在 `git add && git commit` 同一命令里先于 add 运行
     if command -v radon &> /dev/null; then
-        RADON_OUTPUT=$(radon cc "$CODE_DIR" -n C -s 2>&1 || true)
-        if echo "$RADON_OUTPUT" | grep -qE '^\s+[FMC]\s'; then
-            ERRORS+="[radon] 存在圈复杂度 ≥ C 的函数：\n$RADON_OUTPUT\n"
+        mapfile -t CHANGED_PY < <(git diff HEAD --name-only --diff-filter=AM -- "$CODE_DIR" | grep '\.py$' || true)
+        if [[ ${#CHANGED_PY[@]} -gt 0 ]]; then
+            TOUCHED=$(git diff HEAD -U0 -- "${CHANGED_PY[@]}" | python3 -c '
+import json, re, subprocess, sys
+hunks, path = {}, None
+for line in sys.stdin:
+    if line.startswith("+++ "):
+        path = line[6:].strip() if line.startswith("+++ b/") else None
+    m = re.match(r"@@ -\S+ \+(\d+)(?:,(\d+))? @@", line)
+    if m and path:
+        start, count = int(m.group(1)), int(m.group(2) or 1)
+        hunks.setdefault(path, []).append((start, start + max(count, 1) - 1))
+data = json.loads(subprocess.run(["radon", "cc", "-j", "-n", "C", *hunks], capture_output=True, text=True).stdout or "{}")
+for path, blocks in data.items():
+    for b in blocks if isinstance(blocks, list) else []:
+        if any(s <= b["endline"] and e >= b["lineno"] for s, e in hunks.get(path, [])):
+            print("%s:%s %s - %s (%s)" % (path, b["lineno"], b["name"], b["rank"], b["complexity"]))
+' 2>&1 || true)
+            if [[ -n "$TOUCHED" ]]; then
+                ERRORS+="[radon] 本次改动触及的函数圈复杂度 ≥ C：\n$TOUCHED\n"
+            fi
+        fi
+        LEGACY_COUNT=$(radon cc "$CODE_DIR" -n C 2>/dev/null | grep -cE '^\s+[FMC]\s' || true)
+        if [[ "$LEGACY_COUNT" -gt 0 ]]; then
+            WARNINGS+="[radon] $CODE_DIR/ 存量 ${LEGACY_COUNT} 个函数圈复杂度 ≥ C(未被本次改动触及,不阻塞)。\n"
         fi
     fi