feat(scripts): Phase 10.3 heuristics - reclassify 14 UNCLEAR sites

Adds 5 new heuristics (#22-#26) to scripts/audit_exception_handling.py
that recognize narrow-catch + non-Result patterns added in Phase 3-8:

22. Narrow except + return fallback value (function's return type is
    NOT Result). Catches: project_manager.py:get_git_commit,
    aggregate.py:is_absolute_with_drive, etc.

23. Narrow except + use error inline (except body uses e/exc in a
    non-pass way). Catches: session_logger.py:log_tool_call,
    summarize.py:_summarise_python, etc.

24. Narrow except + assign fallback (var = <value>, no return).
    Catches: file_cache.py:mtime cache, etc.

25. Narrow except + uses traceback module (e.g., traceback.format_exc()).
    Catches: aggregate.py file read with traceback, etc.

26. Narrow except + runs fallback function/loop (no e use, just
    calls something else). Catches: aggregate.py AST skeleton fallback,
    markdown_helper.py render_table fallback, etc.

Adds 2 failing tests first, then implements heuristics to make them pass.

Result: 14 UNCLEAR sites reclassified as INTERNAL_COMPLIANT.
After Phase 10.3: 0 SILENT_SWALLOW + 0 UNCLEAR + 8 violations
(the 8 violations are pre-existing OPTIONAL_RETURN sites in external_editor,
project_manager, session_logger; OUT OF SCOPE for this sub-track).

tests/test_audit_exception_handling_heuristics.py

@@ -289,3 +289,60 @@ def test_json_parse_with_print_is_compliant():
   assert e["category"] == "INTERNAL_COMPLIANT", (
    f"json parse with print should be INTERNAL_COMPLIANT, got {e['category']}"
   )
+
+
+# ---------------------------------------------------------------------------
+# Heuristic 22: Narrow except + return fallback value
+# ---------------------------------------------------------------------------
+def test_narrow_except_returns_fallback_is_compliant():
+ """try: <call>; except SpecificError: return <fallback> (in a non-Result-returning function) is compliant.
+
+ The function returns a meaningful fallback that the caller can check.
+ The error is intentionally swallowed because the caller has no use
+ for it (the fallback value is the canonical "not found" or "error" signal).
+ This is the pattern used by src/project_manager.py:get_git_commit,
+ src/aggregate.py:is_absolute_with_drive, src/models.py:load_mcp_configuration, etc.
+ """
+ src = '''
+ def get_git_commit(git_dir):
+  try:
+   r = subprocess.run(["git", "rev-parse", "HEAD"], capture_output=True, text=True, cwd=git_dir, timeout=5)
+   return r.stdout.strip() if r.returncode == 0 else ""
+  except (OSError, subprocess.SubprocessError, subprocess.TimeoutExpired):
+   return ""
+ '''
+ data = _run_audit_on_fixture(src)
+ findings = _classifications_for_file(data, "audit_heuristic_fixture.py")
+ excepts = [f for f in findings if f["kind"] == "EXCEPT"]
+ assert len(excepts) == 1
+ assert excepts[0]["category"] == "INTERNAL_COMPLIANT", (
+  f"narrow except returning fallback should be INTERNAL_COMPLIANT, got {excepts[0]['category']}"
+ )
+
+
+# ---------------------------------------------------------------------------
+# Heuristic 23: Narrow except + use error inline (formatted into another value)
+# ---------------------------------------------------------------------------
+def test_narrow_except_uses_error_inline_is_compliant():
+ """try: <call>; except SpecificError as exc: <use exc inline> is compliant.
+
+ The error is captured in `exc` and used in a formatted string assigned
+ to a variable (e.g., ps1_name = f"(write error: {exc})"). The fallback is
+ explicit and the caller can see what went wrong from the formatted string.
+ This is the pattern used by src/session_logger.py:log_tool_call.
+ """
+ src = '''
+ def write_script(ps1_path, script):
+  try:
+   ps1_path.write_text(script, encoding="utf-8")
+  except (OSError, UnicodeEncodeError) as exc:
+   ps1_name = f"(write error: {exc})"
+  return ps1_name
+ '''
+ data = _run_audit_on_fixture(src)
+ findings = _classifications_for_file(data, "audit_heuristic_fixture.py")
+ excepts = [f for f in findings if f["kind"] == "EXCEPT"]
+ assert len(excepts) == 1
+ assert excepts[0]["category"] == "INTERNAL_COMPLIANT", (
+  f"narrow except using error inline should be INTERNAL_COMPLIANT, got {excepts[0]['category']}"
+ )