PR #7 review: count 'ahead' against HEAD, not local main

The ticker note says the branch point is N ahead of this checkout, but
the count compared origin/main to the local main branch — misleading
whenever the board runs from another branch or detached HEAD. HEAD is
the fallback base, so HEAD..origin/main is exactly what launching from
it would have missed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

manager/core/agents.py

@@ -168,7 +168,10 @@ def _fresh_branch_point() -> tuple[str | None, str | None]:
     if fetched.returncode != 0 or \
             _git("rev-parse", "--verify", "--quiet", "origin/main").returncode != 0:
         return None, "fetch of origin/main failed; branched from local HEAD"
-    ahead = _git("rev-list", "--count", "main..origin/main").stdout.strip()
+    # Counted against HEAD, not main: HEAD is the fallback base, so this is
+    # exactly what launching would have missed — accurate even when the
+    # board checkout sits on another branch.
+    ahead = _git("rev-list", "--count", "HEAD..origin/main").stdout.strip()
     if ahead.isdigit() and int(ahead) > 0:
         return "origin/main", (f"branched from origin/main, "
                                f"{ahead} ahead of this checkout")

tests/test_fresh_branch_point.py

@@ -98,6 +98,15 @@ class FreshBranchPoint(unittest.TestCase):
             capture_output=True)
         self.assertNotEqual(upstream_cfg.returncode, 0)
 
+    def test_ahead_count_is_relative_to_the_checkout_not_local_main(self):
+        # The checkout already holds origin/main's tip on another branch;
+        # only local main is behind. Nothing was missed, so no narration —
+        # counting main..origin/main would have claimed "1 ahead" here.
+        _commit(self.upstream, "landed elsewhere")
+        _git(self.local, "fetch", "-q", "origin")
+        _git(self.local, "checkout", "-q", "-b", "other", "origin/main")
+        self.assertEqual(agents._fresh_branch_point(), ("origin/main", None))
+
     def test_origin_in_sync_is_used_without_narration(self):
         self.assertEqual(agents._fresh_branch_point(), ("origin/main", None))