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/cli/test_manual_compress.py

@@ -21,6 +21,7 @@ def test_manual_compress_reports_noop_without_success_banner(capsys):
     shell.agent = MagicMock()
     shell.agent.compression_enabled = True
     shell.agent._cached_system_prompt = ""
+    shell.agent.session_id = shell.session_id  # no-op compression: no split
     shell.agent._compress_context.return_value = (list(history), "")
 
     def _estimate(messages):
@@ -48,6 +49,7 @@ def test_manual_compress_explains_when_token_estimate_rises(capsys):
     shell.agent = MagicMock()
     shell.agent.compression_enabled = True
     shell.agent._cached_system_prompt = ""
+    shell.agent.session_id = shell.session_id  # no-op: no split
     shell.agent._compress_context.return_value = (compressed, "")
 
     def _estimate(messages):
@@ -64,3 +66,64 @@ def test_manual_compress_explains_when_token_estimate_rises(capsys):
     assert "✅ Compressed: 4 → 3 messages" in output
     assert "Rough transcript estimate: ~100 → ~120 tokens" in output
     assert "denser summaries" in output
+
+
+def test_manual_compress_syncs_session_id_after_split():
+    """Regression for cli.session_id desync after /compress.
+
+    _compress_context ends the parent session and creates a new child session,
+    mutating agent.session_id. Without syncing, cli.session_id still points
+    at the ended parent — causing /status, /resume, exit summary, and the
+    next end_session() call (e.g. from /resume <id>) to target the wrong row.
+    """
+    shell = _make_cli()
+    history = _make_history()
+    old_id = shell.session_id
+    new_child_id = "20260101_000000_child1"
+
+    compressed = [
+        {"role": "user", "content": "[summary]"},
+        history[-1],
+    ]
+    shell.conversation_history = history
+    shell.agent = MagicMock()
+    shell.agent.compression_enabled = True
+    shell.agent._cached_system_prompt = ""
+    # Simulate _compress_context mutating agent.session_id as a side effect.
+    def _fake_compress(*args, **kwargs):
+        shell.agent.session_id = new_child_id
+        return (compressed, "")
+    shell.agent._compress_context.side_effect = _fake_compress
+    shell.agent.session_id = old_id  # starts in sync
+    shell._pending_title = "stale title"
+
+    with patch("agent.model_metadata.estimate_messages_tokens_rough", return_value=100):
+        shell._manual_compress()
+
+    # CLI session_id must now point at the continuation child, not the parent.
+    assert shell.session_id == new_child_id
+    assert shell.session_id != old_id
+    # Pending title must be cleared — titles belong to the parent lineage and
+    # get regenerated for the continuation.
+    assert shell._pending_title is None
+
+
+def test_manual_compress_no_sync_when_session_id_unchanged():
+    """If compression is a no-op (agent.session_id didn't change), the CLI
+    must NOT clear _pending_title or otherwise disturb session state.
+    """
+    shell = _make_cli()
+    history = _make_history()
+    shell.conversation_history = history
+    shell.agent = MagicMock()
+    shell.agent.compression_enabled = True
+    shell.agent._cached_system_prompt = ""
+    shell.agent.session_id = shell.session_id
+    shell.agent._compress_context.return_value = (list(history), "")
+    shell._pending_title = "keep me"
+
+    with patch("agent.model_metadata.estimate_messages_tokens_rough", return_value=100):
+        shell._manual_compress()
+
+    # No split → pending title untouched.
+    assert shell._pending_title == "keep me"