fix(council): let the Claude Code session id win over --session

A claim made with --session <name> stored the name, but the PreToolUse gate compares the hook payload's session_id, so the gate refused every edit of the claiming session and a later release without the flag exited 3. caller() now takes CLAUDE_CODE_SESSION_ID whenever it is set and falls back to --session only for other runtimes. test_council covers a claim and release with --session under a Claude Code session (negative control against the old caller fails). Claims made with --session before this fix go stale after an hour without a heartbeat and can then be taken over.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_council.py

@@ -62,6 +62,11 @@ class TestCouncil(unittest.TestCase):
         self._run("s1", "claim", "work/x", "--work", "w")
         self.assertEqual(self._run("s2", "takeover", "work/x", "--work", "w").returncode, 3)
 
+    def test_session_flag_cannot_hide_the_claude_code_session(self):
+        self._run("s1", "claim", "work/x", "--work", "w", "--session", "One")
+        self.assertIn('"session": "s1"', (self.root / "work/x/claim.json").read_text())
+        self.assertEqual(self._run("s1", "release", "work/x", "--session", "One").returncode, 0)
+
     def test_only_the_holder_releases(self):
         self._run("s1", "claim", "work/x", "--work", "w")
         self.assertEqual(self._run("s2", "release", "work/x").returncode, 3)