fix(traffic): the traffic layer reads STALE, not LIVE, on cached flow tiles

Once the TomTom tile budget is spent, or TomTom fails, the proxy serves
cached tiles marked STALE-BUDGET / STALE-ERROR. flowSource works out
`stale`, but the layer fetched flow through fetchFlowForBounds, which
returns only the segments, so getStats() and the sync chip still read
"LIVE · Roads: …". #1239 fixed the get_traffic_flow tool the same way; the
layer now uses fetchFlowDetail too, reports stale and oldestTileAt in its
stats, and the chip reads "STALE · Roads: <source> · Flow: cached TomTom
tiles". A source without fetchFlowDetail keeps the previous behaviour.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/layers/traffic/roadModes.test.mjs

@@ -283,6 +283,64 @@ test('flow application preserves direct values and leaves Hybrid fill simulated'
   assert.equal(state._flowPending, 0);
 });
 
+test('stale proxy flow tiles reach the layer stats and never read LIVE', async () => {
+  const { createFlow } = await import('./flow.js');
+  const { createModel } = await import('./model.js');
+  const { createControls } = await import('./controls.js');
+  const { createState } = await import('./state.js');
+  const { layerFeedState } = await import('../../data/feedState.js');
+  let detail = {
+    segments: [flow],
+    partial: false,
+    stale: true,
+    oldestTileAt: 1000,
+  };
+  const source = {
+    fetchFlowDetail: async () => detail,
+    fetchFlowForBounds: async () => detail.segments,
+    getFlowSessionStats: () => ({ tilesFetched: 1 }),
+  };
+  const state = createState({ services: {} });
+  Object.assign(state, {
+    _enabled: true,
+    _liveMode: true,
+    _loadGeneration: 1,
+    _flowStatusPromise: Promise.resolve(),
+    _bucketCounts: { free: 3, slow: 0, jam: 0, sim: 1 },
+  });
+  const parts = {};
+  const context = { state, services: { credits: {} }, parts, source };
+  parts.model = createModel(context);
+  parts.flow = createFlow(context);
+  const controls = createControls(context);
+
+  await parts.flow.applyFlowToRoads([{ coords: coordinates }], box, 1);
+  const stale = controls.methods.getStats();
+  assert.equal(stale.mode, 'live');
+  assert.equal(stale.stale, true);
+  assert.equal(stale.oldestTileAt, 1000);
+  assert.doesNotMatch(stale.loadingLabel, /LIVE/);
+  assert.equal(layerFeedState(stale), 'stale');
+
+  // A road failure outranks cached flow: the row reads the failure.
+  state._roadError = 'Road geometry unavailable';
+  assert.equal(controls.methods.getStats().stale, false);
+  state._roadError = null;
+
+  detail = {
+    segments: [flow],
+    partial: false,
+    stale: false,
+    oldestTileAt: 2000,
+  };
+  state._loadGeneration = 2;
+  await parts.flow.applyFlowToRoads([{ coords: coordinates }], box, 2);
+  const live = controls.methods.getStats();
+  assert.equal(live.stale, false);
+  assert.match(live.loadingLabel, /^LIVE · Roads: OpenStreetMap/);
+  assert.equal(layerFeedState(live), 'nominal');
+});
+
 test('status names the drawn road source for each mode', async () => {
   const { createModel } = await import('./model.js');
   const { trafficFeedPresentation: present } = createModel({