Separate live observation sources from aircraft and vessel layers

src/sources/live/aircraft.js

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+import { admitRecords, cleanText, coordinates, epoch, finite } from './contract.js';
+
+/** Normalize the OpenSky state-vector route, including its regional fallback. */
+export function normalizeOpenSkyAircraft(row) {
+  if (!Array.isArray(row)) return null;
+  const id = cleanText(row[0]).toLowerCase();
+  if (!id || !coordinates(row[6], row[5])) return null;
+  return {
+    id, reference: id, latitude: row[6], longitude: row[5],
+    callsign: cleanText(row[1]), originCountry: cleanText(row[2]),
+    positionTimeMs: epoch(row[3], 1000), contactTimeMs: epoch(row[4], 1000),
+    baroAltitudeM: finite(row[7]), ellipsoidAltitudeM: finite(row[13]),
+    onGround: row[8] === true, speedMps: finite(row[9]), courseDeg: finite(row[10]),
+    verticalRateMps: finite(row[11]), category: finite(row[17]),
+    typeCode: null, registration: null, operator: null,
+  };
+}
+
+/** Normalize readsb observations. The caller supplies the source snapshot epoch. */
+export function normalizeReadsbAircraft(row, snapshotTimeMs) {
+  const id = cleanText(row?.hex).toLowerCase();
+  const latitude = finite(row?.lat), longitude = finite(row?.lon);
+  if (!id || !coordinates(latitude, longitude)) return null;
+  const baroFt = finite(row.alt_baro), geoFt = finite(row.alt_geom);
+  const speedKts = finite(row.gs), rateFtMin = finite(row.baro_rate);
+  const seen = finite(row.seen), seenPos = finite(row.seen_pos);
+  return {
+    id, reference: id, latitude, longitude,
+    callsign: cleanText(row.flight), originCountry: null,
+    positionTimeMs: snapshotTimeMs == null ? null : snapshotTimeMs - (seenPos ?? 0) * 1000,
+    contactTimeMs: snapshotTimeMs == null || seen == null ? null : snapshotTimeMs - seen * 1000,
+    baroAltitudeM: baroFt == null ? null : baroFt * 0.3048,
+    ellipsoidAltitudeM: geoFt == null ? null : geoFt * 0.3048,
+    onGround: cleanText(row.alt_baro).toLowerCase() === 'ground',
+    speedMps: speedKts == null ? null : speedKts * 0.514444,
+    courseDeg: finite(row.track), verticalRateMps: rateFtMin == null ? null : rateFtMin * 0.00508,
+    category: row.category ?? null, typeCode: cleanText(row.t),
+    registration: cleanText(row.r), operator: cleanText(row.ownOp),
+  };
+}
+
+export function openSkySnapshot(payload, { source = 'OpenSky Network', coverage = 'worldwide upstream snapshot', now = Date.now(), stale = false } = {}) {
+  const admitted = admitRecords(payload?.states, normalizeOpenSkyAircraft, 'OpenSky');
+  const observedAtMs = epoch(payload?.time, 1000);
+  const ageMs = observedAtMs == null ? null : Math.max(0, now - observedAtMs);
+  return { ...admitted, source, coverage, observedAtMs, ageMs,
+    stale: stale || (ageMs != null && ageMs > 120000),
+    freshness: observedAtMs == null ? 'unknown' : (stale || ageMs > 120000) ? 'stale' : 'current',
+  };
+}
+
+export function readsbSnapshot(payload, { observedAtMs, source = 'adsb.lol', coverage = 'military upstream snapshot', now = Date.now(), stale = false } = {}) {
+  const admitted = admitRecords(payload?.ac, row => normalizeReadsbAircraft(row, observedAtMs), 'adsb.lol');
+  const ageMs = observedAtMs == null ? null : Math.max(0, now - observedAtMs);
+  return { ...admitted, source, coverage, observedAtMs, ageMs, stale,
+    freshness: observedAtMs == null ? 'unknown' : stale ? 'stale' : 'current',
+  };
+}
+
+/** Track altitude remains barometric; renderers choose a visual ground fallback. */
+export function normalizeAircraftTrack(rows, { baseTimeMs = 0, readsb = false } = {}) {
+  if (!Array.isArray(rows)) return [];
+  return rows.flatMap(row => {
+    if (!Array.isArray(row)) return [];
+    const latitude = finite(row[1]), longitude = finite(row[2]);
+    const offset = finite(row[0]);
+    const observedAtMs = offset == null ? null : baseTimeMs + offset * 1000;
+    if (!coordinates(latitude, longitude) || observedAtMs == null || observedAtMs <= 0) return [];
+    const altitude = finite(row[3]);
+    return [{ latitude, longitude, observedAtMs,
+      baroAltitudeM: altitude == null ? null : altitude * (readsb ? 0.3048 : 1),
+      ellipsoidAltitudeM: null,
+      onGround: readsb ? cleanText(row[3]).toLowerCase() === 'ground' : row[5] === true,
+    }];
+  });
+}

src/sources/live/contract.js

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+/**
+ * Browser live-source contract. Coordinates are WGS84 degrees; lengths and
+ * velocities are metres and metres/second; times are Unix milliseconds.
+ * Barometric altitude and ellipsoid altitude are separate, nullable observations.
+ * A missing timestamp is unknown, never the time the response was received.
+ *
+ * Sources expose getSnapshot(query, { signal }) and optionally
+ * getTrack(reference, { signal }). References are opaque to consumers.
+ * Snapshots describe coverage and completeness independently of freshness.
+ * Records contain observation data only, with no scene objects or transport data.
+ */
+export class LiveSourceError extends Error {
+  constructor(code, message, { status = null, retryAfterMs = 20000, source = null } = {}) {
+    super(message);
+    this.name = 'LiveSourceError';
+    this.code = code;
+    this.status = status;
+    this.retryAfterMs = retryAfterMs;
+    this.source = source;
+  }
+}
+
+export function finite(value) {
+  if (value == null || value === '' || typeof value === 'boolean') return null;
+  const number = Number(value);
+  return Number.isFinite(number) ? number : null;
+}
+
+export function epoch(value, scale = 1) {
+  const number = finite(value);
+  return number != null && number > 0 ? number * scale : null;
+}
+
+export function cleanText(value) {
+  return typeof value === 'string' ? value.trim() : '';
+}
+
+export function coordinates(latitude, longitude) {
+  return Number.isFinite(latitude) && Math.abs(latitude) <= 90
+    && Number.isFinite(longitude) && Math.abs(longitude) <= 180;
+}
+
+/** Admit a snapshot atomically; an all-invalid nonempty feed is unavailable. */
+export function admitRecords(rows, normalize, label) {
+  if (!Array.isArray(rows)) throw new LiveSourceError('malformed', `Malformed ${label} response`);
+  const records = [];
+  const ids = new Set();
+  for (const row of rows) {
+    const record = normalize(row);
+    if (record && !ids.has(record.id)) {
+      records.push(record);
+      ids.add(record.id);
+    }
+  }
+  if (rows.length && !records.length) {
+    throw new LiveSourceError('malformed', `Malformed ${label} aircraft rows`);
+  }
+  return { records, complete: records.length === rows.length, rejectedCount: rows.length - records.length };
+}
+
+/** Cancellation is checked after body parsing even when a transport ignores it. */
+export async function readResponse(fetchImpl, url, { signal, ...init } = {}, source = 'Live source') {
+  signal?.throwIfAborted();
+  let response;
+  try {
+    response = await fetchImpl(url, { ...init, signal });
+    signal?.throwIfAborted();
+  } catch (error) {
+    signal?.throwIfAborted();
+    if (error?.name === 'AbortError') throw error;
+    throw new LiveSourceError('unavailable', `${source} network error`, { source });
+  }
+  let payload = null;
+  try { payload = await response.json(); } catch { /* classified below */ }
+  signal?.throwIfAborted();
+  return { response, payload };
+}
+
+export function httpError(response, source) {
+  const status = response.status;
+  const code = status === 429 ? 'limited' : status === 401 || status === 403 ? 'denied' : 'unavailable';
+  return new LiveSourceError(code, status === 429 ? `${source} rate limited` : `${source} HTTP ${status}`, {
+    status, source, retryAfterMs: code === 'limited' || code === 'denied' ? 45000 : 20000,
+  });
+}

src/sources/live/contract.test.mjs

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+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { createOpenSkySource, createAdsbLolSource, createAisStreamSource, normalizeReadsbAircraft, normalizeVesselObservation, openSkySnapshot, readsbSnapshot } from './index.js';
+
+const now = 1800000000000;
+const aircraft = ['AbC123', 'TEST', 'Example', now / 1000 - 15, now / 1000 - 2, -97, 30, 1000, false, 100, 250, -2, null, 1040];
+const response = (payload, headers = {}, status = 200) => Response.json(payload, { headers, status });
+
+test('civil observations retain identity, separate altitude datums and source epochs', () => {
+  const snapshot = openSkySnapshot({ time: now / 1000 - 130, states: [aircraft] }, { now, source: 'Test source', coverage: 'regional' });
+  const row = snapshot.records[0];
+  assert.equal(row.id, 'abc123');
+  assert.equal(row.baroAltitudeM, 1000);
+  assert.equal(row.ellipsoidAltitudeM, 1040);
+  assert.equal(row.positionTimeMs, now - 15000);
+  assert.equal(row.contactTimeMs, now - 2000);
+  assert.equal(snapshot.ageMs, 130000);
+  assert.equal(snapshot.freshness, 'stale');
+  assert.equal(snapshot.coverage, 'regional');
+  const missing = openSkySnapshot({ states: [[...aircraft.slice(0, 3), null, null, ...aircraft.slice(5)]] }, { now });
+  assert.equal(missing.observedAtMs, null);
+  assert.equal(missing.freshness, 'unknown');
+  assert.equal(missing.records[0].positionTimeMs, null);
+});
+
+test('mixed-invalid and duplicate admissions are explicitly incomplete; all-invalid rejects', () => {
+  const invalid = [...aircraft]; invalid[5] = 181;
+  const partial = openSkySnapshot({ states: [aircraft, invalid, aircraft] });
+  assert.equal(partial.records.length, 1);
+  assert.equal(partial.complete, false);
+  assert.equal(partial.rejectedCount, 2);
+  assert.throws(() => openSkySnapshot({ states: [invalid] }), { code: 'malformed' });
+  assert.throws(() => openSkySnapshot({}), { code: 'malformed' });
+  assert.equal(openSkySnapshot({ states: [] }).complete, true);
+});
+
+test('readsb units and position/contact ages are normalized once against the source epoch', () => {
+  const row = normalizeReadsbAircraft({ hex: 'abc123', lat: '30', lon: '-97', alt_baro: 10000, alt_geom: 10100, gs: 120, baro_rate: -600, seen: 2, seen_pos: 12 }, now);
+  assert.equal(row.baroAltitudeM, 3048);
+  assert.equal(row.ellipsoidAltitudeM, 3078.48);
+  assert.equal(row.speedMps, 120 * 0.514444);
+  assert.equal(row.verticalRateMps, -600 * 0.00508);
+  assert.equal(row.positionTimeMs, now - 12000);
+  assert.equal(row.contactTimeMs, now - 2000);
+  const ground = normalizeReadsbAircraft({ hex: 'abc123', lat: 30, lon: -97, alt_baro: 'ground' }, null);
+  assert.equal(ground.onGround, true);
+  assert.equal(ground.baroAltitudeM, null);
+  assert.equal(ground.positionTimeMs, null);
+  assert.equal(readsbSnapshot({ ac: [] }, { observedAtMs: null }).freshness, 'unknown');
+});
+
+test('vessel identity, opaque reference and heading/course remain distinct, unknowns stay null', () => {
+  const row = normalizeVesselObservation({ mmsi: '123456789', lat: 30, lon: -97, speed: 10, heading: 45, course: 60, last_position_epoch: now / 1000, extra: 'discard' }, 'opaque-reference');
+  assert.equal(row.id, '123456789');
+  assert.equal(row.reference, 'opaque-reference');
+  assert.equal(row.headingDeg, 45);
+  assert.equal(row.courseDeg, 60);
+  assert.equal(row.speedMps, 10 * 0.514444);
+  assert.equal(row.altitudeDatum, 'sea-surface');
+  assert.equal(row.observedAtMs, now);
+  assert.equal('extra' in row, false);
+  assert.equal(normalizeVesselObservation({ mmsi: 'x', lat: null, lon: null }), null);
+});
+
+test('construction is inert; adapters preserve routes, viewport query, cache epoch and history datum', async () => {
+  const requests = [];
+  const fetchImpl = async (url, init) => {
+    requests.push({ url, init });
+    if (url.startsWith('/api/opensky?')) return response({ time: now / 1000, states: [aircraft] }, { 'x-flight-source': 'adsb.lol', 'x-flight-coverage': '250 nm regional' });
+    if (url.startsWith('/api/opensky-track')) return response({ path: [[now / 1000 - 30, 30, -97, 1000, 45, false]] });
+    if (url === '/api/adsblol/mil') return response({ ac: [{ hex: 'abc123', lat: 30, lon: -97, seen_pos: 15 }] }, { 'x-ads-b-cache-age-ms': '60000', 'x-ads-b-cache': 'STALE' });
+    return response({ timestamp: now / 1000 - 60, trace: [[10, 30, -97, 1000]] });
+  };
+  const civil = createOpenSkySource({ fetchImpl, now: () => now });
+  const military = createAdsbLolSource({ fetchImpl, now: () => now });
+  assert.equal(requests.length, 0);
+  const signal = new AbortController().signal;
+  const snapshot = await civil.getSnapshot({ latitude: 30.123456, longitude: -97 }, { signal });
+  assert.equal(requests[0].url, '/api/opensky?lat=30.1235&lon=-97.0000');
+  assert.equal(requests[0].init.signal, signal);
+  assert.equal(snapshot.source, 'adsb.lol');
+  assert.equal(snapshot.coverage, '250 nm regional');
+  assert.equal((await civil.getTrack('abc123')).records[0].baroAltitudeM, 1000);
+  const mil = await military.getSnapshot();
+  assert.equal(mil.observedAtMs, now - 60000);
+  assert.equal(mil.records[0].positionTimeMs, now - 75000);
+  assert.equal(mil.stale, true);
+  const track = await military.getTrack('abc123');
+  assert.equal(track.complete, false);
+  assert.equal(track.records[0].observedAtMs, now - 50000);
+  assert.equal(track.records[0].baroAltitudeM, 304.8);
+  assert.equal(track.records[0].ellipsoidAltitudeM, null);
+});
+
+test('cancellation after slow body parsing rejects even with a transport that ignores abort', async () => {
+  let release;
+  const controller = new AbortController();
+  const source = createOpenSkySource({ fetchImpl: async () => ({ ok: true, json: () => new Promise(resolve => { release = resolve; }) }) });
+  const pending = source.getSnapshot({}, { signal: controller.signal });
+  await new Promise(resolve => setImmediate(resolve));
+  controller.abort();
+  release({ states: [aircraft] });
+  await assert.rejects(pending, { name: 'AbortError' });
+});
+
+test('denials and outages never start another source and do not echo arbitrary response bodies', async () => {
+  for (const status of [401, 403, 429, 502]) {
+    let calls = 0;
+    const source = createOpenSkySource({ fetchImpl: async () => { calls++; return response({ error: 'sensitive upstream detail' }, {}, status); } });
+    await assert.rejects(source.getSnapshot(), error => {
+      assert.equal(error.status, status);
+      assert.equal(error.message.includes('sensitive'), false);
+      assert.ok(error.retryAfterMs >= 20000);
+      return true;
+    });
+    assert.equal(calls, 1);
+  }
+});
+
+test('AIS reports limited received coverage and keeps connection state separate from positions', async () => {
+  const source = createAisStreamSource({ origin: () => 'http://example.test', fetchImpl: async url => {
+    if (url.includes('/track?')) return response({ samples: [{ lat: 30, lon: -97, t: now / 1000 }] });
+    assert.equal(url, 'http://example.test/api/ais-live?maxRows=500');
+    return response({ status: 'reconnecting', refreshing: true, rows: [{ mmsi: '123456789', lat: 30, lon: -97, last_position_UTC: new Date(now).toISOString() }], newestPositionAt: new Date(now).toISOString() });
+  } });
+  const snapshot = await source.getSnapshot({ maxRows: 500 });
+  assert.equal(snapshot.complete, false);
+  assert.equal(snapshot.stale, true);
+  assert.equal(snapshot.observedAtMs, now);
+  assert.equal(snapshot.transportStatus, 'reconnecting');
+  assert.equal((await source.getTrack('123456789')).records[0].observedAtMs, now);
+});

src/sources/live/index.js

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+export { LiveSourceError } from './contract.js';
+export { normalizeOpenSkyAircraft, normalizeReadsbAircraft, normalizeAircraftTrack, openSkySnapshot, readsbSnapshot } from './aircraft.js';
+export { normalizeVesselObservation, normalizeVesselTrack, vesselSnapshot } from './vessels.js';
+export { createOpenSkySource, createAdsbLolSource, createAisStreamSource } from './standalone.js';

src/sources/live/standalone.js

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+import { epoch, finite, httpError, LiveSourceError, readResponse } from './contract.js';
+import { normalizeAircraftTrack, openSkySnapshot, readsbSnapshot } from './aircraft.js';
+import { normalizeVesselTrack, vesselSnapshot } from './vessels.js';
+
+const defaultFetch = (...args) => globalThis.fetch(...args);
+const header = (response, name) => response.headers?.get?.(name);
+
+function openSkyError(response) {
+  const error = httpError(response, 'OpenSky');
+  const mode = String(header(response, 'x-opensky-auth-mode-used') || header(response, 'x-opensky-auth') || '').toLowerCase();
+  const reason = String(header(response, 'x-opensky-auth-reason') || '').toLowerCase();
+  if (response.status === 429 && (!mode || mode === 'anon')) error.message = 'OpenSky rate limited (anonymous)';
+  if (response.status === 401 || response.status === 403) {
+    const reasons = {
+      oauth_invalid_or_missing: 'OpenSky OAuth client missing/invalid',
+      oauth_invalid_credentials: 'OpenSky OAuth rejected credentials',
+      basic_invalid_credentials: 'OpenSky username/password rejected',
+      missing_basic_creds: 'OpenSky auth missing',
+      missing_oauth_and_basic_creds: 'OpenSky auth missing',
+      auth_required: 'OpenSky auth required', forced_anonymous: 'OpenSky auth required',
+    };
+    error.message = reasons[reason] || (/^(oauth_|basic_)/.test(reason) ? 'OpenSky auth invalid' : mode === 'anon' ? 'OpenSky auth required' : 'OpenSky auth failed');
+  }
+  return error;
+}
+
+/** Existing same-origin aircraft routes; no request starts during construction. */
+export function createOpenSkySource({ fetchImpl = defaultFetch, now = () => Date.now() } = {}) {
+  return {
+    async getSnapshot(query = {}, { signal } = {}) {
+      const params = new URLSearchParams();
+      if (Number.isFinite(query.latitude) && Number.isFinite(query.longitude)) {
+        params.set('lat', query.latitude.toFixed(4)); params.set('lon', query.longitude.toFixed(4));
+      }
+      const { response, payload } = await readResponse(fetchImpl, `/api/opensky${params.size ? '?' + params : ''}`, { signal }, 'OpenSky');
+      if (!response.ok) throw openSkyError(response);
+      return { ...openSkySnapshot(payload, {
+        source: header(response, 'x-flight-source') || 'OpenSky Network',
+        coverage: header(response, 'x-flight-coverage') || 'worldwide upstream snapshot', now: now(),
+      }), status: response.status };
+    },
+    async getTrack(reference, { signal } = {}) {
+      const { response, payload } = await readResponse(fetchImpl, '/api/opensky-track?icao24=' + encodeURIComponent(reference), { signal }, 'OpenSky');
+      if (!response.ok) throw httpError(response, 'OpenSky');
+      return { records: normalizeAircraftTrack(payload?.path), complete: false };
+    },
+    async getEnrichment(query, { signal } = {}) {
+      if (!['type', 'route'].includes(query.kind)) throw new LiveSourceError('unsupported', 'Enrichment unavailable');
+      const { response, payload } = await readResponse(fetchImpl, `/api/adsbdb/${query.kind}/${encodeURIComponent(query.id)}`, { signal }, 'adsbdb');
+      if (!response.ok) throw httpError(response, 'adsbdb');
+      return payload;
+    },
+  };
+}
+
+export function createAdsbLolSource({ fetchImpl = defaultFetch, now = () => Date.now() } = {}) {
+  return {
+    async getSnapshot(_query = {}, { signal } = {}) {
+      const { response, payload } = await readResponse(fetchImpl, '/api/adsblol/mil', { signal }, 'adsb.lol');
+      if (!response.ok) throw httpError(response, 'adsb.lol');
+      const age = finite(header(response, 'x-ads-b-cache-age-ms'));
+      return { ...readsbSnapshot(payload, {
+        observedAtMs: now() - (age != null && age > 0 ? age : 0), now: now(),
+        stale: header(response, 'x-ads-b-cache') === 'STALE',
+      }), status: response.status };
+    },
+    async getTrack(reference, { signal } = {}) {
+      const { response, payload } = await readResponse(fetchImpl, '/api/adsblol/trace?hex=' + encodeURIComponent(reference), { signal }, 'adsb.lol');
+      if (!response.ok) throw httpError(response, 'adsb.lol');
+      const baseTimeMs = epoch(payload?.timestamp, 1000);
+      return { records: baseTimeMs == null ? [] : normalizeAircraftTrack(payload?.trace, { baseTimeMs, readsb: true }), complete: false };
+    },
+  };
+}
+
+export function createAisStreamSource({ fetchImpl = defaultFetch, apiUrl = '/api/ais-live', origin = () => globalThis.location?.origin || 'http://localhost' } = {}) {
+  return {
+    async getSnapshot({ maxRows = 12000 } = {}, { signal } = {}) {
+      const url = new URL(apiUrl, origin());
+      url.searchParams.set('maxRows', String(maxRows));
+      const { response, payload } = await readResponse(fetchImpl, url.toString(), { signal, cache: 'no-store' }, 'AIS live');
+      if (!response.ok) {
+        const error = httpError(response, 'AIS live');
+        const reasons = { 'missing-key': 'AISSTREAM_API_KEY not set', 'auth-failed': 'API key rejected — check AISSTREAM_API_KEY', unsupported: 'live feed unsupported', error: 'feed down', closed: 'feed disconnected' };
+        error.message = reasons[payload?.status] || error.message;
+        throw error;
+      }
+      return { ...vesselSnapshot(payload), status: response.status };
+    },
+    async getTrack(reference, { signal } = {}) {
+      const { response, payload } = await readResponse(fetchImpl, '/api/ais-live/track?mmsi=' + encodeURIComponent(reference), { signal }, 'AIS live');
+      if (!response.ok) throw httpError(response, 'AIS live');
+      return { records: normalizeVesselTrack(payload?.samples), complete: false };
+    },
+  };
+}

src/sources/live/vessels.js

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+import { coordinates, epoch, finite, LiveSourceError } from './contract.js';
+
+/** AIS positions are sea-surface observations; heading and course are distinct. */
+export function normalizeVesselObservation(row, reference = null) {
+  const id = String(row?.mmsi || row?.input_identifier || '').trim();
+  const latitude = finite(row?.lat), longitude = finite(row?.lon);
+  if (!id || !coordinates(latitude, longitude)) return null;
+  const speedKts = finite(row.speed);
+  return {
+    id, reference: reference ?? id, latitude, longitude,
+    name: String(row.name || row.input_name || id),
+    imo: String(row.imo || ''), type: String(row.type_specific || row.type || ''),
+    destination: String(row.destination || ''),
+    speedMps: speedKts == null ? null : speedKts * 0.514444,
+    courseDeg: finite(row.course), headingDeg: finite(row.heading),
+    observedAtMs: epoch(row.last_position_epoch, 1000)
+      ?? epoch(Date.parse(row.last_position_UTC)),
+    altitudeDatum: 'sea-surface',
+  };
+}
+
+export function vesselSnapshot(payload, { source = 'AISStream', coverage = 'received AIS positions', referenceFor = row => String(row.mmsi || row.input_identifier || '') } = {}) {
+  if (!Array.isArray(payload?.rows)) throw new LiveSourceError('malformed', 'Malformed vessel response');
+  const rows = payload.rows;
+  const records = [], ids = new Set();
+  for (const row of rows) {
+    const record = normalizeVesselObservation(row, referenceFor(row));
+    if (record && !ids.has(record.id)) { records.push(record); ids.add(record.id); }
+  }
+  const observedAtMs = epoch(payload?.newestPositionAt) ?? epoch(Date.parse(payload?.newestPositionAt))
+    ?? records.reduce((newest, row) => Math.max(newest || 0, row.observedAtMs || 0) || null, null);
+  return {
+    records, source, coverage, complete: false, rejectedCount: rows.length - records.length,
+    observedAtMs, freshness: payload?.refreshing ? 'stale' : observedAtMs == null ? 'unknown' : 'current',
+    stale: Boolean(payload?.refreshing),
+    // Connection state is distinct from receipt of a usable position.
+    transportStatus: typeof payload?.status === 'string' ? payload.status : null,
+    lastMessageAt: payload?.lastMessageAt ?? null,
+    nextAttemptAt: finite(payload?.nextAttemptAt), silentForMs: finite(payload?.silentForMs),
+    reconnectAttempt: finite(payload?.reconnectAttempt), rawRowCount: rows.length,
+  };
+}
+
+export function normalizeVesselTrack(samples) {
+  if (!Array.isArray(samples)) return [];
+  return samples.flatMap(sample => {
+    const latitude = finite(sample?.lat), longitude = finite(sample?.lon);
+    if (!coordinates(latitude, longitude)) return [];
+    return [{ latitude, longitude, observedAtMs: epoch(sample?.t, 1000), altitudeDatum: 'sea-surface' }];
+  });
+}