stage-6: model selection and advanced commands

/model (show/change), /restart (owner), /logs, set_session_model API, model reset on /clear. 20 new tests (161 total).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_claude_session.py

@@ -20,6 +20,7 @@ from src.claude_session import (
     list_sessions,
     resume_session,
     send_message,
+    set_session_model,
     start_session,
 )
 
@@ -574,3 +575,46 @@ class TestListSessions:
             claude_session, "_SESSIONS_FILE", tmp_path / "nonexistent.json"
         )
         assert list_sessions() == {}
+
+
+# ---------------------------------------------------------------------------
+# set_session_model
+# ---------------------------------------------------------------------------
+
+
+class TestSetSessionModel:
+    def test_updates_model_in_active_json(self, tmp_path, monkeypatch):
+        sessions_dir = tmp_path / "sessions"
+        sessions_dir.mkdir()
+        sf = sessions_dir / "active.json"
+        monkeypatch.setattr(claude_session, "SESSIONS_DIR", sessions_dir)
+        monkeypatch.setattr(claude_session, "_SESSIONS_FILE", sf)
+
+        sf.write_text(json.dumps({
+            "general": {
+                "session_id": "abc",
+                "model": "sonnet",
+                "message_count": 1,
+            }
+        }))
+
+        result = set_session_model("general", "opus")
+        assert result is True
+
+        data = json.loads(sf.read_text())
+        assert data["general"]["model"] == "opus"
+
+    def test_returns_false_when_no_session(self, tmp_path, monkeypatch):
+        sessions_dir = tmp_path / "sessions"
+        sessions_dir.mkdir()
+        sf = sessions_dir / "active.json"
+        monkeypatch.setattr(claude_session, "SESSIONS_DIR", sessions_dir)
+        monkeypatch.setattr(claude_session, "_SESSIONS_FILE", sf)
+
+        sf.write_text("{}")
+        result = set_session_model("general", "opus")
+        assert result is False
+
+    def test_invalid_model_raises(self):
+        with pytest.raises(ValueError, match="Invalid model"):
+            set_session_model("general", "gpt4")