fix(cli): sync session_id after compression and preserve original end_reason (#12920)

After context compression (manual /compress or auto), run_agent's
_compress_context ends the current session and creates a new continuation
child session, mutating agent.session_id. The classic CLI held its own
self.session_id that never resynced, so /status showed the ended parent,
the exit-summary --resume hint pointed at a closed row, and any later
end_session() call (from /resume <other> or /branch) targeted the wrong
row AND overwrote the parent's 'compression' end_reason.

This only affected the classic prompt_toolkit CLI. The gateway path was
already fixed in PR #1160 (March 2026); --tui and ACP use different
session plumbing and were unaffected.

Changes:
- cli.py::_manual_compress — sync self.session_id from self.agent.session_id
  after _compress_context, clear _pending_title
- cli.py chat loop — same sync post-run_conversation for auto-compression
- cli.py hermes -q single-query mode — same sync so stderr session_id
  output points at the continuation
- hermes_state.py::end_session — guard UPDATE with 'ended_at IS NULL' so
  the first end_reason wins; reopen_session() remains the explicit
  escape hatch for re-ending a closed row

Tests:
- 3 new in tests/cli/test_manual_compress.py (split sync, no-op guard,
  pending_title behavior)
- 2 new in tests/test_hermes_state.py (preserve compression end_reason
  on double-end; reopen-then-re-end still works)

Closes #12483. Credits @steve5636 for the same-day bug report and
@dieutx for PR #3529 which proposed the CLI sync approach.

hermes_state.py

@@ -383,10 +383,19 @@ class SessionDB:
         return session_id
 
     def end_session(self, session_id: str, end_reason: str) -> None:
-        """Mark a session as ended."""
+        """Mark a session as ended.
+
+        No-ops when the session is already ended. The first end_reason wins:
+        compression-split sessions must keep their ``end_reason = 'compression'``
+        record even if a later stale ``end_session()`` call (e.g. from a
+        desynced CLI session_id after ``/resume`` or ``/branch``) targets them
+        with a different reason. Use ``reopen_session()`` first if you
+        intentionally need to re-end a closed session with a new reason.
+        """
         def _do(conn):
             conn.execute(
-                "UPDATE sessions SET ended_at = ?, end_reason = ? WHERE id = ?",
+                "UPDATE sessions SET ended_at = ?, end_reason = ? "
+                "WHERE id = ? AND ended_at IS NULL",
                 (time.time(), end_reason, session_id),
             )
         self._execute_write(_do)