flightjar

Add a new notification channel type (Discord, Slack, Pushover, Matrix, SMTP, Signal, …) to the alerts pipeline. Covers the new sealed-record subclass, the JsonConverter branch, the INotifier impl, DI registration in Program.cs, the Alerts dialog UI (FIELDS map + add button + persistence), and the notifier tests. Use when the user asks to add a new notification channel ("send alerts to Discord", "support Pushover", "wire up Matrix alerts"). Don't use for changing existing notifier behaviour (Telegram formatting, ntfy priority map, etc) — those are one-file edits to the specific notifier.

Add or change anonymous PostHog telemetry — extend the per-tick `instance_ping` payload, add a new property to the `$identify` `$set`, fire a backend event from a hot path, or wire a frontend `track()` call. Covers the privacy posture (no exact coords / IPs / tokens / per-aircraft IDs, $geoip_disable, coarse 10° region, bucketed receiver-fingerprint values), the file map, the build-time `PosthogApiKey` MSBuild prop, the `TELEMETRY_ENABLED=0` opt-out, and the tests + README to update. Use when the user asks "add X to telemetry", "send Y to PostHog", "track when the user does Z", "is N safe to log", or anything touching `app/static/telemetry.js` / `FlightJar.Api/Telemetry/`. Don't use for the `/metrics` Prometheus endpoint or `/api/stats` — those are operator-facing and unrelated.

Add or debug Playwright end-to-end tests under tests/e2e/. Covers the FlightJar harness setup (BEAST pointed at a dead host, deterministic env-var pins, reuseExistingServer caveats), the per-test localStorage reset pattern, how to inspect DOM state via page.evaluate(), how to find a layer/dialog row reliably, and the Leaflet/CDN quirks (most notably L.Control.Layers._checkDisabledLayers clobbering input.disabled). Use when writing a new tests/e2e/*.spec.js, when an existing Playwright test is failing intermittently or in unexpected ways, or when you need to assert on something rendered by a third-party library (Leaflet, Recharts, etc.).

Add a new HTTP endpoint to the FlightJar API — either a map/data endpoint under /api/ or an operational one like /healthz. Covers DI-via-parameter-injection, the bbox-validation pattern for spatial queries, snake_case JSON responses, the "feature disabled → return a structured payload, not 500" convention, and the `[Collection("SequentialApi")]` WebApplicationFactory tests. Use when the user asks to add a new endpoint ("add /api/X", "expose Y over HTTP", "add a reset/recompute POST for Z"). Don't use for WebSocket / SSE / streaming work.

Add a new in-memory reference-data loader under FlightJar.Core.ReferenceData — CSV/JSON/TSV file baked into the Docker image with an optional /data/ override, loaded once at startup into a FrozenDictionary or similar, exposed via a DI-registered singleton. Use when the user wants to bundle a new lookup set — military-callsign prefixes, type-designator → wake-turbulence category, runway data, FIR boundaries, aircraft silhouettes, ICAO24 allocation blocks. Covers the loader class, the DI wiring, the Dockerfile fetch, the `LoadFirstAvailableAsync` path convention, and the test pattern. Do NOT use for external HTTP data sources (that's `external-client-add`), per-aircraft trails, or anything that changes mid-run.

Extend the left-hand aircraft sidebar — add a new sort chip, a new list-filter chip, a new per-row metric, or a new header/status element. Covers the fingerprint-cache invariant that makes every per-row change subtle (miss a field and the row stops re-rendering when it changes), the lastX cached-text pattern for header elements, delegated event wiring, and the escapeHtml discipline for user-sourced strings. Use when the user asks for "sort by X", "add a MIL/watched/whatever filter chip", "show field Y in each row", or "add a status pill to the sidebar". Don't use for the aircraft detail panel (that's `detail-panel-section`), dialogs, or the map overlays.

Port a Mode S Comm-B BDS register decoder from pyModeS into FlightJar.Decoder.ModeS.CommB, wire it into the aircraft registry + snapshot + detail panel, and verify against pyModeS golden vectors. Use when the user asks to add a new BDS register (e.g. "add BDS 4,5 hazard data", "decode the hazard / windshear register", "show pilot-entered MET data"). The four heuristic registers 4,0 / 4,4 / 5,0 / 6,0 are already implemented; remaining candidates are BDS 4,5 (meteorological hazard — opt-in, noisy), and the format-ID registers BDS 1,0 / 1,7 / 2,0 / 3,0 (data link capability, GICB capability report, aircraft identification, ACAS active resolution).

Add a new section (grid of metric tiles, or custom block) to the aircraft detail panel in app/static/detail_panel.js. Use when the user asks to show additional per-aircraft info in the floating card — fuel state, waypoints, winds-aloft, ACARS, extra Mode S registers, anything per-plane. Covers the DOM placeholder / per-tick mutator split, help-icon wiring, CSS conventions, and the Playwright smoke that catches layout + width regressions. Do NOT use this for sidebar changes, header, or dialogs — those live elsewhere.

Add a new typed HTTP client for an external data source (like a new route-lookup API, flight database, weather provider, photo service), wired into the snapshot enrichment pipeline with the standard CachedLookup + disk cache + 429 throttle pattern. Use when the user asks to integrate a new upstream data source — e.g. "add FlightRadar24 lookups", "pull winds aloft from NOAA", "fetch runway data from OurAirports". Don't use for local reference data bundled into the image (aircraft_db.csv.gz et al); those live under FlightJar.Core/ReferenceData.

Quickly verify a frontend change in-browser without regenerating screenshots. Boots the FlightJar backend in the Playwright harness config (BEAST pointed at a dead host, blackspots off), injects a fake snapshot, opens the detail panel, and checks for console errors. Use when the user asks to "test the UI", "smoke-check the panel", "verify this renders correctly", or after any app/static/* change you need to confirm works in a real browser. Do NOT use for capturing screenshots — that's the screenshots skill.

Add a new toggleable overlay to the Leaflet map (layers control checkbox on the top-right). Handles the proxy-overlay pattern (dispatching to a setter that manages data loading + rendering), wires persistence of the checkbox state, and plugs into the existing layers-control registry. Use when the user asks to add a map overlay — weather radar, flight paths, wind barbs, surface winds, METAR stations, MLAT coverage, custom GeoJSON. For changes to base tiles (OpenStreetMap / Satellite / Topographic) see the `baseLayers` block in map_setup.js directly.

Regenerate the README screenshots (desktop + mobile) by running scripts/take_screenshots.js against a freshly-built backend and inspecting the resulting PNGs. Use when the user asks to refresh, update, or re-take the screenshots, or whenever a UI change has landed that would invalidate the current set. The script self-hosts the backend, injects a fake fleet, fetches a real aircraft photo from Wikimedia Commons, and mocks /api/aircraft + /api/blackspots + /api/stats + /api/coverage + /api/heatmap + /api/polar_heatmap so every dialog reads like a real-world install with weeks of data.