feat(tui): add Diagnostics panel for stored evidence

Toggle a Diagnostics panel with i, built on the Activity readout. It swaps
in for the Drive pane and shows the decoded critical_warning, power-on
hours, power cycles, unsafe shutdowns, media errors and available spare
with their change over the selection, and per-hour (Day) or per-day
(History) temperature min/avg/max, active/idle/powered-off/unknown split
and coverage. History bars draw reads beside writes while it is open, and a
set critical_warning shows as a badge in the endurance outlook without
affecting the projection. Counter deltas are withheld across a controller
segment change.

tests/test_tui_diagnostics.py

@@ -0,0 +1,154 @@
+"""Diagnostics panel on the dashboard (issue #109): toggle, render, badge."""
+import sqlite3
+
+import pytest
+from test_dashboard_design import dashboard, visible  # noqa: F401  (fixtures)
+
+from fenris.activity_plot import VolumePoint
+from fenris.tui import FenrisTuiApp, HelpScreen, HistoryGraph
+
+
+def _store(app):
+    return sqlite3.connect(app.store_path)
+
+
+def _set_latest_warning(app, value):
+    conn = _store(app)
+    conn.execute(
+        "UPDATE samples SET critical_warning = ?, power_on_hours = id, "
+        "unsafe_shutdowns = id / 20 WHERE 1", (value,))
+    conn.commit()
+    conn.close()
+
+
+async def _settle(app, pilot):
+    app.on_refresh_tick()
+    await pilot.pause()
+
+
+def _text(app, selector):
+    return str(app.query_one(selector).render())
+
+
+def test_i_is_a_declared_binding_and_d_stays_disclosures():
+    keys = {b.key: b.action for b in FenrisTuiApp.BINDINGS}
+    assert keys["i"] == "toggle_diagnostics"
+    assert keys["d"] == "disclose"
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("size", [(140, 44), (100, 30)])
+async def test_i_toggles_the_diagnostics_panel_and_hides_the_drive_pane(dashboard, size):  # noqa: F811
+    app = dashboard
+    _set_latest_warning(app, 0)
+    async with app.run_test(size=size) as pilot:
+        await _settle(app, pilot)
+        assert not app.query_one("#diagnostics-panel").display
+        assert app.query_one("#drive-panel").display
+        await pilot.press("i")
+        await _settle(app, pilot)
+        assert app.query_one("#diagnostics-panel").display
+        assert not app.query_one("#drive-panel").display
+        body = _text(app, "#diagnostics")
+        assert "Diagnostics" in body and "Critical warning none" in body
+        assert "Power-on hours 61 Δ +60" in body
+        await pilot.press("i")
+        await _settle(app, pilot)
+        assert not app.query_one("#diagnostics-panel").display
+        assert app.query_one("#drive-panel").display
+
+
+@pytest.mark.asyncio
+async def test_footer_and_help_list_the_diagnostics_key(dashboard):  # noqa: F811
+    app = dashboard
+    async with app.run_test(size=(140, 40)) as pilot:
+        await _settle(app, pilot)
+        assert "i Diagnostics" in _text(app, "#action-rail")
+        await pilot.press("?")
+        assert isinstance(app.screen, HelpScreen)
+        assert "Diagnostics" in str(app.screen.query_one("#help-text").render())
+
+
+@pytest.mark.asyncio
+async def test_diagnostics_follow_the_activity_view(dashboard):  # noqa: F811
+    app = dashboard
+    async with app.run_test(size=(140, 44)) as pilot:
+        await _settle(app, pilot)
+        await pilot.press("i")
+        await _settle(app, pilot)
+        assert "last 3h" in _text(app, "#diagnostics")
+        await pilot.press("v")  # Day
+        await _settle(app, pilot)
+        body = _text(app, "#diagnostics")
+        assert "· day 20" in body and "Hours ·" in body
+        await pilot.press("v")  # History
+        await _settle(app, pilot)
+        assert "last 14 days" in _text(app, "#diagnostics")
+
+
+@pytest.mark.asyncio
+async def test_critical_warning_badge_shows_in_the_outlook_without_the_panel(dashboard):  # noqa: F811
+    app = dashboard
+    _set_latest_warning(app, 0x04)
+    async with app.run_test(size=(140, 44)) as pilot:
+        await _settle(app, pilot)
+        assert not app.query_one("#diagnostics-panel").display
+        band = _text(app, "#headline-band")
+        assert "0x04" in band and "reliability degraded" in band
+
+
+@pytest.mark.asyncio
+async def test_no_badge_when_the_drive_reports_no_warning(dashboard):  # noqa: F811
+    app = dashboard
+    _set_latest_warning(app, 0)
+    async with app.run_test(size=(140, 44)) as pilot:
+        await _settle(app, pilot)
+        assert "critical warning" not in _text(app, "#headline-band").lower()
+
+
+@pytest.mark.asyncio
+async def test_diagnostics_work_in_constrained_mode(dashboard):  # noqa: F811
+    app = dashboard
+    _set_latest_warning(app, 0x01)
+    async with app.run_test(size=(60, 20)) as pilot:
+        await _settle(app, pilot)
+        assert app._is_constrained_mode
+        await pilot.press("i")
+        await _settle(app, pilot)
+        assert app.query_one("#diagnostics-panel").display
+        body = _text(app, "#diagnostics")
+        assert "available spare below threshold" in body
+        assert "Power-on hours" in body
+        await pilot.press("i")
+        await _settle(app, pilot)
+        assert app.query_one("#drive-panel").display
+
+
+@pytest.mark.asyncio
+async def test_toggling_while_zoomed_restores_the_grid_and_keeps_focus(dashboard):  # noqa: F811
+    app = dashboard
+    async with app.run_test(size=(140, 44)) as pilot:
+        await _settle(app, pilot)
+        await pilot.press("z")
+        await pilot.press("i")
+        await _settle(app, pilot)
+        assert app._zoomed_panel is None
+        assert app.focused is not None
+
+
+@pytest.mark.asyncio
+async def test_history_bars_draw_reads_alongside_writes_only_with_diagnostics(dashboard):  # noqa: F811
+    app = dashboard
+    async with app.run_test(size=(140, 44)) as pilot:
+        await _settle(app, pilot)
+        await pilot.press("v", "v")  # History
+        await _settle(app, pilot)
+        graph = app.query_one(HistoryGraph)
+        assert "Reads" not in _text(app, "#bar-legend")
+        await pilot.press("i")
+        await _settle(app, pilot)
+        legend = _text(app, "#bar-legend")
+        assert "Writes" in legend and "Reads" in legend
+        await pilot.press("i")
+        await _settle(app, pilot)
+        assert "Reads" not in _text(app, "#bar-legend")