fix(traffic): stop a few matched roads reading as "no matches"

The live flow status derived its wording from the rounded coverage
percent, so 1 matched dot among 300 rounded to 0% and read
"SIMULATED ... (no matches)", and 1 simulated dot among 300 rounded to
100% and dropped "Unmatched: simulated". Coverage now stays within 1-99%
whenever both matched and simulated dots are shown.

src/layers/traffic/controls.js

@@ -259,7 +259,8 @@ export function createControls({ state: layerState, services, parts, source }) {
      * `error` carries this instant's health, so a live-configured layer whose
      * flow feed went down reads DEGRADED with the reason instead of a stale
      * LIVE coverage number. `flowCoveragePct` is shown dots on matched roads /
-     * all shown dots (0–100 int), excluding closures; `tilesFetched` counts flow-tile requests
+     * all shown dots (0–100 int, kept within 1–99 while both kinds are shown),
+     * excluding closures; `tilesFetched` counts flow-tile requests
      * issued to the proxy this session (decode-cache hits excluded).
      * @returns {{count:number, lastUpdate:number|null, loading:boolean,
      *   mode:'live'|'sim', error:string|null, flowCoveragePct:number,
@@ -304,8 +305,18 @@ export function createControls({ state: layerState, services, parts, source }) {
         Boolean(layerState._heightPending);
       const { free, slow, jam, sim } = layerState._bucketCounts;
       const matched = free + slow + jam;
+      // The label reads 0 as "no matches" and 100 as nothing simulated, so
+      // rounding must not reach either while both kinds of dot are shown.
       const flowCoveragePct =
-        matched + sim > 0 ? Math.round((100 * matched) / (matched + sim)) : 0;
+        matched + sim > 0
+          ? Math.min(
+              sim > 0 ? 99 : 100,
+              Math.max(
+                matched > 0 ? 1 : 0,
+                Math.round((100 * matched) / (matched + sim)),
+              ),
+            )
+          : 0;
       const feed = parts.model.trafficFeedPresentation({
         liveMode: layerState._liveMode,
         fetching: loading,

src/layers/traffic/source.test.mjs

@@ -516,6 +516,26 @@ test('late closures hide and stop dots; coverage counts shown matched dots, and
   assert.equal(controls.getStats().flowCoveragePct, 80);
 });
 
+test('coverage never rounds to "no matches" or full coverage while both kinds of dot are shown', async () => {
+  const { state, controls } = await matchingContext(async () => []);
+  state._bucketCounts = { free: 1, slow: 0, jam: 0, sim: 300 };
+  assert.equal(controls.getStats().flowCoveragePct, 1);
+  assert.equal(
+    controls.getStats().loadingLabel,
+    'LIVE · Roads: OpenStreetMap · Flow: TomTom · 1% cov · Unmatched: simulated',
+  );
+  state._bucketCounts = { free: 300, slow: 0, jam: 0, sim: 1 };
+  assert.equal(controls.getStats().flowCoveragePct, 99);
+  assert.equal(
+    controls.getStats().loadingLabel,
+    'LIVE · Roads: OpenStreetMap · Flow: TomTom · 99% cov · Unmatched: simulated',
+  );
+  state._bucketCounts = { free: 300, slow: 0, jam: 0, sim: 0 };
+  assert.equal(controls.getStats().flowCoveragePct, 100);
+  state._bucketCounts = { free: 0, slow: 0, jam: 0, sim: 300 };
+  assert.equal(controls.getStats().flowCoveragePct, 0);
+});
+
 test('refresh failure removes cached matches and reports simulated flow', async () => {
   const { flow, state, model, controls } = await matchingContext(async () => {
     throw new Error('HTTP 429');