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.

tests/test_hermes_state.py

@@ -46,6 +46,37 @@ class TestSessionLifecycle:
         assert isinstance(session["ended_at"], float)
         assert session["end_reason"] == "user_exit"
 
+    def test_end_session_preserves_original_end_reason(self, db):
+        """The first end_reason wins — compression splits must not be
+        overwritten when a later stale ``end_session()`` call lands on the
+        same row (e.g. from a CLI session_id that desynced after compression
+        and then tried to /resume another session).
+        """
+        db.create_session(session_id="s1", source="cli")
+        db.end_session("s1", end_reason="compression")
+        first_ended_at = db.get_session("s1")["ended_at"]
+
+        # Simulate a stale CLI holding the old session_id and calling
+        # end_session() again with a different reason.
+        time.sleep(0.01)
+        db.end_session("s1", end_reason="resumed_other")
+
+        session = db.get_session("s1")
+        assert session["end_reason"] == "compression"
+        assert session["ended_at"] == first_ended_at
+
+    def test_end_session_after_reopen_allows_re_end(self, db):
+        """reopen_session() is the explicit escape hatch for re-ending a
+        closed session. After reopen, end_session() takes effect again.
+        """
+        db.create_session(session_id="s1", source="cli")
+        db.end_session("s1", end_reason="compression")
+        db.reopen_session("s1")
+        db.end_session("s1", end_reason="user_exit")
+
+        session = db.get_session("s1")
+        assert session["end_reason"] == "user_exit"
+
     def test_update_system_prompt(self, db):
         db.create_session(session_id="s1", source="cli")
         db.update_system_prompt("s1", "You are a helpful assistant.")