fix: newest lease marker wins so release ends prior claims

find_active_reviewer_lease walked past terminal markers and re-armed
older claimed leases after gitea_release_reviewer_pr_lease. Treat the
newest marker as authoritative (append-only ledger).

Closes #577

tests/test_reviewer_pr_lease.py

@@ -98,6 +98,45 @@ class TestReviewerLeaseFreshness(unittest.TestCase):
         )
 
 
+class TestReviewerLeaseNewestWins(unittest.TestCase):
+    """#577: terminal release must supersede older claimed markers."""
+
+    def test_released_after_claimed_has_no_active_lease(self):
+        claim = _lease_comment(516, "session-a", phase="claimed")
+        claim["id"] = 1
+        release = _lease_comment(516, "session-a", phase="released")
+        release["id"] = 2
+        active = leases.find_active_reviewer_lease(
+            [claim, release], pr_number=516
+        )
+        self.assertIsNone(active)
+
+    def test_new_claim_after_release_is_active(self):
+        claim = _lease_comment(516, "session-a", phase="claimed")
+        claim["id"] = 1
+        release = _lease_comment(516, "session-a", phase="released")
+        release["id"] = 2
+        reclaim = _lease_comment(516, "session-b", phase="claimed")
+        reclaim["id"] = 3
+        active = leases.find_active_reviewer_lease(
+            [claim, release, reclaim], pr_number=516
+        )
+        self.assertIsNotNone(active)
+        self.assertEqual(active.get("session_id"), "session-b")
+        self.assertEqual(active.get("phase"), "claimed")
+        self.assertEqual(active.get("comment_id"), 3)
+
+    def test_done_after_claimed_has_no_active_lease(self):
+        claim = _lease_comment(516, "session-a", phase="claimed")
+        claim["id"] = 10
+        done = _lease_comment(516, "session-a", phase="done")
+        done["id"] = 11
+        active = leases.find_active_reviewer_lease(
+            [claim, done], pr_number=516
+        )
+        self.assertIsNone(active)
+
+
 class TestReviewerLeaseMutationGate(unittest.TestCase):
     def setUp(self):
         leases.clear_session_lease()