feat(transit): live public-transit vehicles from open GTFS-Realtime feeds (#587)

Supersedes #218 by @spcpza, ported onto the current component layout with fixes from review.

Verified before merge: format, package boundaries, unit suite, build, and the browser tracking suite; a browser harness for the change where one applies; adversarial review applied.

Contributor: @spcpza. His original commit is the base of this branch, and his own re-port onto main (2026-09-15, `5b69011`) was consulted while finishing the height work. That port reads every vehicle's surface from the app's shared ground-floor system (`cachedGroundFloor` / `warmGroundFloor` / `GROUND_FLOOR_LIFT_M`) rather than sampling the scene per layer, keeps a vehicle hidden until its cell answers, warms a bounded batch per poll on a timer instead of per frame, and renders at the ellipsoid above the altitude gate. That is the sounder primitive — one floor system for the app, with the rooftop-versus-street question already settled against a datum-correct DEM prior — and this branch's height work was rebuilt on it, replacing a bespoke cell cache, ground prior and rooftop rule written here. Credit for that direction is his.

Future work (not in this PR), both written up in docs/CURRENT-STATE.md:

- Readable route names. The realtime feeds carry only `route_id`; `route_short_name` / `route_long_name` live in each operator's static GTFS `routes.txt`, and headsigns in `trips.txt`. Doing it properly wants a server-side metadata loader beside the transit proxy with fixed registered static sources, bounded indexes built once and persisted, a slow conditional refresh, and a versioned route dictionary the browser caches. Shipped here: ids are never rewritten, and a cut one carries an ellipsis instead of reading as a typo.
- Below-ground rendering. Subway vehicles are drawn on the surface directly above themselves, because the feeds carry no depth and a train nobody can see is not worth drawing; the card says so plainly. Real treatment wants OSM tunnel geometry per city and a ghosted sprite tethered to the surface. The owner recorded it and left it.

Round four and after (2026-09-15). The owner tested round three under FLIR and NVG, and then asked for the design to be taken further: elegant in performance, beautiful on camera, trails with a cache for public transport, Cesium-native, and a core other moving layers can adopt. Codex Astra reviewed the plan (it confirmed the speed fault: a glide started from the drawn position at receipt time but spanned the gap between report times, so with MBTA reporting every ~10 s against a 15 s poll every second glide ran at 1.5x; it rejected a queued-segment patch), then wrote the design, then implemented it in commit-sized passes with adversarial review between them and real-browser harness runs by the integrator.

What this PR now contains beyond the contributor's original port:

- Delayed playback in a contact-agnostic core (`src/data/contactPlayback.js`): each vehicle keeps a typed, bounded fix history and a display clock that runs at one second per second through it, a feed-derived lag behind real time, holding at its newest fix rather than extrapolating and never sprinting to catch up. Marker, course, motion word, card and trail all read the same displayed sample. The clock has an explicit time-offset and seek API so a rewind is a later feature, not a rewrite; flights and vessels are untouched.
- A selected-vehicle trail (`src/data/contactTrailRenderer.js`, `src/layers/transit/trails.js`): the retained history drawn with batched Cesium primitives, clipped at display time so the head is exactly the sprite, faded by age, in the mode colour (white under sensor presets), on the same surface path as the marker.
- Bounded proxy-side history (`server/providers/transitHistory.js`): fifteen minutes and at most 128 fixes per vehicle with hard byte ceilings, MBTA only for now (opt-in per feed), served by a small endpoint that never fetches upstream, so a selected trail survives a browser reload while the server keeps running.
- Scene work bounded to what is visible and moving, an occluder, cached DETECT candidates, holds on the render loop only while something visible moves.
- Sensor presets: white-hot haloed sprites under NVG/FLIR/noir (black-hot inverts), saturated mode colours under CRT, per-mode bracket tiers in every theme, the selected card keeping its mode colour.
- A discriminating browser harness (`scripts/qa-transit.mjs`) that samples postRender frames, reads the real card anchor, and measures fleet budgets at 800 and 3,000 vehicles.

Not built, recorded as follow-ups: curated route display names (lowest priority per the owner), fleet-wide tails, route snapping, a rewind UI, adoption of the playback core by flights and vessels.

Verified at merge (2026-09-15 morning): unit suite 3,896 passing, build clean, format and boundary gates clean, tracking regression 109/109, browser harness keyless 200 pass / 0 fail (13 sensor checks unexercised because the live view offered fewer than six isolated sprites; every judged sprite passed), keyed on Google 3D tiles 198 pass with the per-frame allocation gate as the only failure. Follow-ups recorded: the keyed build's playback sampler still allocates per frame (CPU and frame time stay within budget; the 3,000-vehicle metro view sits at a 27.6 ms frame interval against a 25 ms budget), the shared detection overlay's per-paint allocation, friendlier route names, fleet-wide tails, a rewind UI, and adopting the playback core for vessels and flights.
Co-authored-by: spcpza <[email protected]>

DATA_SOURCES.md

@@ -46,6 +46,13 @@ How to read this:
 | **DriveBC** (Government of British Columbia)                          | CCTV camera catalog + frames, British Columbia highways                                                                             | [Open Government Licence – British Columbia](https://www2.gov.bc.ca/gov/content/data/open-data/open-government-licence-bc) — attribution REQUIRED                                                                                                                                                                                                     | "DriveBC. Contains information licensed under the Open Government Licence – British Columbia"                                               |
 | **Open Calgary** (`data.calgary.ca`)                                  | CCTV camera catalog + frames, Calgary                                                                                               | [Open Government Licence – City of Calgary](https://data.calgary.ca/stories/s/Open-Calgary-Terms-of-Use/u45n-7awa) — attribution REQUIRED                                                                                                                                                                                                             | "Contains information licensed under the Open Government Licence – City of Calgary"                                                         |
 | **GBFS (Lyft / BCycle)**                                              | Bikeshare availability                                                                                                              | Per-feed (attribution-only)                                                                                                                                                                                                                                                                                                                           | Credit the operator (e.g. Austin BCycle) + its `license_url`                                                                                |
+| **MBTA / MassDOT** (cdn.mbta.com) | Transit layer live vehicles and up to 15 minutes of recently observed positions, Greater Boston | MBTA / MassDOT open realtime vehicle data, used for the live view and up to fifteen minutes of recently observed positions; published for developer use and not against their use. | Attribution to MBTA / MassDOT (courtesy text) |
+| **CapMetro** (data.texas.gov) | Transit layer live vehicles, Austin TX | CapMetro open realtime vehicle data, used for the live view; published for developer use and not against their use. | Attribution to CapMetro (courtesy text) |
+| **Metro Transit** (Metropolitan Council) | Transit layer live vehicles, Minneapolis–St Paul | Metro Transit / Metropolitan Council open realtime vehicle data, used for the live view; published for developer use and not against their use. | Attribution to Metro Transit / Metropolitan Council (courtesy text) |
+| **OVapi / Stichting OpenGeo** | Transit layer live vehicles, Netherlands | OVapi / Stichting OpenGeo open realtime vehicle data, used for the live view; published for developer use and not against their use. The client sends a User-Agent and conditional requests. | Attribution to OVapi / Stichting OpenGeo (courtesy text) |
+| **Entur** (api.entur.io) | Transit layer live vehicles, Norway | Entur open realtime vehicle data, used for the live view; published for developer use and not against their use. The client sends the `ET-Client-Name` identifying header. | Attribution to Entur (courtesy text) |
+| **TransLink** (Queensland Government) | Transit layer live vehicles, South East Queensland | TransLink / Queensland Government open realtime vehicle data, used for the live view; published for developer use and not against their use. | Attribution to TransLink / Queensland Government (courtesy text) |
+| **HSL** (realtime.hsl.fi) | Transit layer live vehicles, Helsinki | HSL (Helsinki Region Transport) open realtime vehicle data, used for the live view; published for developer use and not against their use. | Attribution to HSL (Helsinki Region Transport) (courtesy text) |
 | **Radio Browser**                                                     | Geolocated internet-radio station directory and station-level tags                                                                  | Public-domain directory data under PDDL 1.0; individual broadcaster stream terms apply                                                                                                                                                                                                                                                                | "Radio Browser" plus a link to the selected broadcaster                                                                                     |
 | **Re:Earth Terrain** (Mapterhorn)                                     | Terrain (keyless globe stacks — OSM etc. — + `/api/terrain/heights` ellipsoidal-height lookups)                                     | Terrain mesh: CC BY 4.0; geoid: EGM2008 (NGA, public domain)                                                                                                                                                                                                                                                                                          | "Terrain (keyless globe stacks): Re:Earth Terrain / Mapterhorn (CC BY 4.0) / EGM2008 (NGA)"                                                 |
 | **OSRM on the FOSSGIS routing servers** (`routing.openstreetmap.de`) | Street-following routes for the Directions layer and voice route annotations, via `/api/route` | [FOSSGIS routing usage policy](https://routing.openstreetmap.de/about.html): "Display the required attribution and display a link to 'fix the map'", "Use a valid user agent and, if applicable, a correct referrer", "One request per second max", "No scraping, no heavy usage". The full policy is the German [FOSSGIS Nutzungsbedingungen](https://www.fossgis.de/arbeitsgruppen/osm-server/nutzungsbedingungen/); FOSSGIS also states that the server may be embedded in your own pages but "eine gewerbliche Nutzung ist nur mit Einschränkungen erlaubt" (commercial use only with restrictions). Route data derives from OpenStreetMap (ODbL 1.0) | "Routing: OSRM on the FOSSGIS servers" + "© OpenStreetMap contributors" + a "fix the map" link — shown in the Data attribution popover |
@@ -67,6 +74,7 @@ How to read this:
 - **Live Traffic NSW cameras.** The camera list is the keyless public `data.livetraffic.com/cameras/traffic-cam.json` feed (Transport for NSW open data, CC BY 4.0); frames are stills on `webcams.transport.nsw.gov.au`, and only that host is registered. That image host answers non-browser clients with an HTML placeholder, so the proxy identifies as a browser for that one host and as itself everywhere else. Frames are fetched at request time and never stored or redistributed. Disable with `CCTV_NSW_ENABLED=0`.
 - **Open Calgary traffic cameras.** Keyless. The camera list is the public Socrata dataset `k7p9-kppz` on `data.calgary.ca`; frames are stills on the city's own `trafficcam.calgary.ca` host, and only that host is registered. Most rows publish an `http://` frame URL and the host redirects those to HTTPS, so URLs are upgraded and pinned to that origin before registration. Frames are fetched at request time and never stored or redistributed. The dataset publishes no camera facing: the `quadrant` field and the quadrant suffix on each camera name are Calgary's address grid, not a bearing, so headings use the shared id-hash fallback at low confidence and are corrected with the in-app calibration gizmo. The licence requires the attribution statement above. Disable with `CCTV_CALGARY_ENABLED=0`.
 - **Camera frame content.** Public camera frames can contain people, vehicles and license plates, and the camera layer does nothing with them beyond putting them on the map. A successful upstream response is relayed as the provider served it: nothing in the camera pipeline blurs, redacts, enhances or restores it, and nothing there runs face, plate or object detection or otherwise recognises or classifies what is in the picture. (The ALPR layer described below maps where plate-reader cameras are, from locations contributors tagged in OpenStreetMap; it reads nothing from any camera frame.) When an upstream has no frame for a camera, what you see instead is a Google Street View still or the app's own placeholder card; the panel's source badge names which of them you are looking at, and a refresh that fails after a frame has arrived leaves the last good picture on screen rather than replacing it. The browser resamples each frame for display: onto a fixed 1920x1080 surface for the camera's projection plane in the scene, and onto a 192x108 canvas for the small ambient card. That scaling is the only change made to the picture, and the only pixels the camera layer reads back are a 64x36 downscale hashed to tell whether the picture has changed. Live streams are piped through; the still path reads the image into memory to pass it on — TxDOT wraps its JPEG in a JSON envelope, which is decoded there — and no frame is written to disk (the disk cache, `.gev-cache/`, holds feed JSON for other layers and never camera imagery). Outside that pipeline, the voice assistant is the one feature that sends imagery anywhere: when it answers a question about what is in view it may attach a downscaled screenshot of the rendered scene — including any camera plane on screen — to the request it sends to the voice model. Frames are fetched only from server-registered camera URLs — a client cannot hand the proxy a URL (see [SECURITY.md](SECURITY.md)). What the app does stays inside the line README draws: no named-person search, no face recognition, no tracking individuals.
+- **Transit (GTFS-Realtime).** The proxy requests only registered operator feeds, validates redirects, bounds responses, and uses conditional requests, short snapshot caching and failure backoff. All seven registered regions are live-enabled; each can be disabled independently. Vehicles use delayed playback between reports, with report age and waiting states shown separately. Session-local selected trails are available for every feed. MBTA additionally retains up to 15 minutes of recently observed positions in the running proxy, so available history can survive a browser reload; server restart clears it. History reads never fetch upstream, and other feeds have no proxy retention. Nothing is archived to disk or collected in the background. Operator text credits are included as a courtesy and do not imply endorsement. Heights are aligned to work with Google 3D tiles; subway markers are shown at street level because these feeds do not supply depth.
 - **Radio Browser.** `/api/radio/stations` discovers official API mirrors, makes bounded and coalesced healthy/geolocated HTTPS-station queries, caches the normalized public-domain directory for 45 minutes, and may serve the last good catalog for up to seven days during an outage. Refreshes must meet minimum accepted-query and station coverage before replacing a warm catalog; schema-valid responses whose rows all fail the product's health policy do not count as successful queries. A usable partial cold catalog is explicitly `DEGRADED`, and malformed or empty successful payloads are rejected atomically. Every directory and click-count request rejects redirects, validates all resolved addresses as globally routable (including reserved/documentation IPv4 and special/non-global IPv6 exclusions), and pins the TLS connection to a validated address. Only MP3/AAC non-HLS directory rows with public HTTPS stream targets are returned; favicons are intentionally omitted. Pressing play connects one browser audio element directly to the selected broadcaster and calls the directory's click counter through known-ID-only `POST /api/radio/click/:uuid`. GEV never proxies, caches, records, bundles, or redistributes audio. Radio Browser supplies station-level tags, not dependable current-song or upcoming-program metadata, so Radio filtering never claims either. Direct playback exposes the listener's IP address to the broadcaster, whose own stream terms apply.
 - **TomTom Traffic.** Optional and BYOK: without `TOMTOM_API_KEY` the traffic layer runs its built-in simulation and no TomTom data (or attribution) appears. With a key, flow vector tiles are fetched through the server-side `/api/tomtom` proxy (120 s cache + a daily tile-budget governor — `TOMTOM_DAILY_TILE_BUDGET`, default 40,000, a configurable application safety ceiling, not a guarantee of staying within TomTom's monthly free allowance; TomTom's [current pricing](https://docs.tomtom.com/pricing/) lists 200K free tile requests per month) and the "Traffic flow data © TomTom" credit is registered in the Data attribution popover the moment live mode activates. TomTom data is served live and cached only transiently (≤120 s TTL under `.gev-cache/`, gitignored) — it is not bundled or redistributed. One 23 KB point-in-time tile snapshot is committed as a decode-test fixture (`src/data/fixtures/`, © TomTom, never served to the app).
 - **Routing (OSRM / FOSSGIS).** `/api/route` proxies the public OSRM instances FOSSGIS e.V. runs for the OpenStreetMap community (car, bike, foot profiles). They are keyless and intended for fair, interactive use — the proxy rate-limits clients (60/min, 200/min total), caps route span and response size, caches each route for 10 minutes, and identifies itself in the User-Agent. Heavy or automated use must run its own OSRM. Routes are computed from OpenStreetMap data (ODbL); the Directions layer and voice routes never redistribute them. A route the router cannot find is reported as such; the Directions layer draws nothing in that case, and voice routes fall back to a clearly labeled straight line.