diff --git a/tests/copilot_usage/test_cli.py b/tests/copilot_usage/test_cli.py
index 1103f07..b16543b 100644
--- a/tests/copilot_usage/test_cli.py
+++ b/tests/copilot_usage/test_cli.py
@@ -518,3 +518,71 @@ def test_start_observer_returns_running_observer(tmp_path: Path) -> None:
         assert observer.is_alive()  # type: ignore[union-attr]
     finally:
         _stop_observer(observer)  # pyright: ignore[reportUnknownArgumentType]
+
+
+# ---------------------------------------------------------------------------
+# _stop_observer(None) guard
+# ---------------------------------------------------------------------------
+
+
+def test_stop_observer_none_is_noop() -> None:
+    """_stop_observer(None) returns silently without raising."""
+    _stop_observer(None)  # should not raise
+
+
+# ---------------------------------------------------------------------------
+# _FileChangeHandler tests
+# ---------------------------------------------------------------------------
+
+
+class TestFileChangeHandler:
+    """Tests for _FileChangeHandler debounce logic."""
+
+    def test_dispatch_sets_event_on_first_call(self) -> None:
+        """First dispatch call within a cold window sets the change_event."""
+        from copilot_usage.cli import (
+            _FileChangeHandler,  # pyright: ignore[reportPrivateUsage]
+        )
+
+        event = threading.Event()
+        handler = _FileChangeHandler(event)
+        handler.dispatch(object())
+        assert event.is_set()
+
+    def test_dispatch_suppresses_within_debounce_window(self) -> None:
+        """Second dispatch call within 2 s is suppressed (debounce)."""
+        import time as _time
+
+        from copilot_usage.cli import (
+            _FileChangeHandler,  # pyright: ignore[reportPrivateUsage]
+        )
+
+        event = threading.Event()
+        handler = _FileChangeHandler(event)
+        handler.dispatch(object())
+        assert event.is_set()
+
+        # Clear and force _last_trigger to now so second call is within debounce
+        event.clear()
+        handler._last_trigger = _time.monotonic()  # pyright: ignore[reportPrivateUsage]
+        handler.dispatch(object())
+        assert not event.is_set()
+
+    def test_dispatch_fires_again_after_debounce_gap(self) -> None:
+        """Dispatch fires again after > 2 s gap."""
+        import time as _time
+
+        from copilot_usage.cli import (
+            _FileChangeHandler,  # pyright: ignore[reportPrivateUsage]
+        )
+
+        event = threading.Event()
+        handler = _FileChangeHandler(event)
+        handler.dispatch(object())
+        assert event.is_set()
+
+        event.clear()
+        # Simulate passage of time by manipulating _last_trigger
+        handler._last_trigger = _time.monotonic() - 3.0  # pyright: ignore[reportPrivateUsage]
+        handler.dispatch(object())
+        assert event.is_set()
diff --git a/tests/copilot_usage/test_parser.py b/tests/copilot_usage/test_parser.py
index a276b67..4578718 100644
--- a/tests/copilot_usage/test_parser.py
+++ b/tests/copilot_usage/test_parser.py
@@ -1826,6 +1826,39 @@ def test_config_without_model_key(self, tmp_path: Path) -> None:
         summary = build_session_summary(events, config_path=config)
         assert summary.model is None
 
+    def test_config_model_integer_returns_none(self, tmp_path: Path) -> None:
+        """config.json with {"model": 42} → model is None."""
+        config = tmp_path / "config.json"
+        config.write_text('{"model": 42}', encoding="utf-8")
+
+        p = tmp_path / "s" / "events.jsonl"
+        _write_events(p, _START_EVENT, _USER_MSG, _ASSISTANT_MSG)
+        events = parse_events(p)
+        summary = build_session_summary(events, config_path=config)
+        assert summary.model is None
+
+    def test_config_model_null_returns_none(self, tmp_path: Path) -> None:
+        """config.json with {"model": null} → model is None."""
+        config = tmp_path / "config.json"
+        config.write_text('{"model": null}', encoding="utf-8")
+
+        p = tmp_path / "s" / "events.jsonl"
+        _write_events(p, _START_EVENT, _USER_MSG, _ASSISTANT_MSG)
+        events = parse_events(p)
+        summary = build_session_summary(events, config_path=config)
+        assert summary.model is None
+
+    def test_config_model_list_returns_none(self, tmp_path: Path) -> None:
+        """config.json with {"model": []} → model is None."""
+        config = tmp_path / "config.json"
+        config.write_text('{"model": []}', encoding="utf-8")
+
+        p = tmp_path / "s" / "events.jsonl"
+        _write_events(p, _START_EVENT, _USER_MSG, _ASSISTANT_MSG)
+        events = parse_events(p)
+        summary = build_session_summary(events, config_path=config)
+        assert summary.model is None
+
 
 # ---------------------------------------------------------------------------
 # build_session_summary — empty session (only session.start)
diff --git a/tests/copilot_usage/test_report.py b/tests/copilot_usage/test_report.py
index a838f9c..a3d2f4e 100644
--- a/tests/copilot_usage/test_report.py
+++ b/tests/copilot_usage/test_report.py
@@ -208,6 +208,27 @@ def test_table_title_contains_active_indicator(self) -> None:
         output = _capture_output([session])
         assert "Active Copilot Sessions" in output
 
+    def test_last_resume_time_used_over_start_time(self) -> None:
+        """When last_resume_time is set, running time is measured from it."""
+        now = datetime.now(tz=UTC)
+        session = SessionSummary(
+            session_id="resume__12345678",
+            name="Resumed",
+            model="claude-sonnet-4",
+            is_active=True,
+            start_time=now - timedelta(days=2),
+            last_resume_time=now - timedelta(minutes=3),
+            user_messages=1,
+            model_metrics={
+                "claude-sonnet-4": ModelMetrics(
+                    usage=TokenUsage(outputTokens=100),
+                )
+            },
+        )
+        output = _capture_output([session])
+        # Should show minutes (from last_resume_time), NOT days (from start_time)
+        assert "2d" not in output and "48h" not in output
+
 
 # ---------------------------------------------------------------------------
 # Helpers for session detail tests
@@ -1137,6 +1158,26 @@ def test_no_historical_data(self) -> None:
         output = _capture_full_summary([session])
         assert "No historical shutdown data" in output
 
+    def test_active_section_uses_last_resume_time(self) -> None:
+        """Active section shows running time from last_resume_time, not start_time."""
+        now = datetime.now(tz=UTC)
+        session = SessionSummary(
+            session_id="resu-5678-abcdef",
+            name="Resumed Session",
+            model="claude-sonnet-4",
+            start_time=now - timedelta(days=3),
+            last_resume_time=now - timedelta(minutes=2),
+            is_active=True,
+            user_messages=1,
+            model_calls=1,
+            active_model_calls=1,
+            active_user_messages=1,
+            active_output_tokens=200,
+        )
+        output = _capture_full_summary([session])
+        # Should show minutes (from last_resume_time), NOT days (from start_time)
+        assert "3d" not in output and "72h" not in output
+
 
 # ---------------------------------------------------------------------------
 # render_cost_view capture helper