fix: don't mark a subject red when only its author is wrong

When a commit failed only CC017 (an AI tool as its author), the diff
showed its subject as a red line, as if the subject had to change. The
subject is now red only when the advice is about it. An empty message
also no longer shows the commit's author where its subject would be.

Author: shenxianpeng

main.py

@@ -1144,12 +1144,18 @@ def _first_value(scope: ScopeResult) -> str:
 
     The text the action piped in when it has it, then the whole message the
     ``message`` rule reports, then whichever rule names a value first. A PR
-    description has no such line: its first line does not identify it.
+    description has no such line: its first line does not identify it. An
+    AI rule's value is the tool or the author it found, never the text, so
+    it never stands in for a commit's subject.
     """
     if scope.label == "PR description":
         return ""
     values = [scope.text, _message_value(scope)]
-    values.extend(str(check.get("value") or "") for check in scope.checks)
+    values.extend(
+        str(check.get("value") or "")
+        for check in scope.checks
+        if check.get("rule_id") not in AI_RULE_IDS
+    )
     for value in values:
         if value.strip():
             return value.strip().splitlines()[0].strip()
@@ -1680,23 +1686,31 @@ def _hunk(scope: ScopeResult, status: str) -> list[str]:
     """
     is_commit = bool(scope.sha) and scope.label.startswith("Commit")
     lines = [f"@@ {scope.sha[:7] if is_commit else scope.label} @@"]
+    value = _first_value(scope)
     removed: list[str] = []
     added: list[str] = []
     advice: list[str] = []
+    # Whether a piece of advice is about the value itself: a subject or a
+    # branch name that has to change. Advice about something else, such as
+    # an AI tool as the commit's author, leaves the subject as context.
+    about_value = False
     for check in _findings(scope, status):
         minus, plus = _line_edits(scope, check)
         removed.extend(minus)
         added.extend(plus)
         if not (minus or plus):
             advice.append(_advice(check))
+            checked = str(check.get("value") or "").strip()
+            about_value |= not checked or checked.splitlines()[0].strip() == value
     if scope.raw_text and not scope.checks:
         advice.append("the output could not be parsed, see the step log")
+        about_value = True
     removed, added, advice = (list(dict.fromkeys(x)) for x in (removed, added, advice))
-    value = _first_value(scope)
     if value and value not in removed:
-        # Advice is about the value itself, so it is what was found; a fix
-        # that only touches other lines leaves it as context.
-        lines.append(f"{'-' if advice else ' '} {value}")
+        # Advice about the value means it is what was found; a fix that only
+        # touches other lines, or advice about something else, leaves it as
+        # context.
+        lines.append(f"{'-' if about_value else ' '} {value}")
     lines.extend(f"- {line}" for line in removed)
     lines.extend(f"+ {line}" for line in added)
     lines.extend(f"# {line}" for line in advice)

main_test.py

@@ -2559,6 +2559,45 @@ def test_advice_is_about_the_value_so_the_value_is_red(self):
             ],
         )
 
+    def test_an_ai_author_leaves_the_subject_as_context(self):
+        # CC017 is about who made the commit, not what its subject says.
+        scope = main.ScopeResult(
+            label="Commit 1/1",
+            sha=SHA_A,
+            text="fix: handle the empty case\n",
+            checks=[
+                make_check(
+                    "message", "pass", "CC001", value="fix: handle the empty case"
+                ),
+                make_check(
+                    "ai_author",
+                    "fail",
+                    "CC017",
+                    value="Claude <noreply@anthropic.com>",
+                    suggest="Commit as yourself",
+                ),
+            ],
+        )
+        self.assertEqual(
+            self._hunks([scope]),
+            ["@@ d87faca @@", "  fix: handle the empty case", "# Commit as yourself"],
+        )
+
+    def test_an_ai_rules_value_never_stands_in_for_the_subject(self):
+        # An empty message has no subject; the author CC017 reports is not one.
+        scope = main.ScopeResult(
+            label="Commit 1/1",
+            sha=SHA_A,
+            checks=[
+                make_check("message", "pass", "CC001"),
+                make_check(
+                    "ai_author", "pass", "CC017", value="Jane <jane@example.com>"
+                ),
+            ],
+        )
+        self.assertEqual(main._first_value(scope), "")
+        self.assertEqual(main._render_scopes([scope], False), ["  ✔ d87faca"])
+
     def test_two_rules_that_ask_for_the_same_line_show_it_once(self):
         scope = ai_scope()
         scope.checks.append({**scope.checks[0], "rule_id": "CC015"})