fix(traffic): name the proxy's own 502/503 accurately (#665)

502 (every mirror unreachable) and 503 (the local limiter, before any mirror
is asked) come from our proxy, so they no longer read as a mirror refusing
the query. Credit the fix in CHANGELOG and note the mapping in CURRENT-STATE.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

src/layers/traffic/source.js

@@ -60,13 +60,20 @@ export function roadRequestError(status) {
       ? 'Overpass rate-limited'
       : code === 504
         ? 'Overpass timed out'
-        : // A source is injected, so a caller's adapter may hand back a
-          // refusal with no status on it. "HTTP undefined" on a panel row is
-          // worse than not naming a number, so an unreadable code falls back
-          // to what `alpr` says when it cannot be more specific either.
-          code === null
-          ? 'Overpass temporarily unavailable'
-          : `Overpass refused the road query (HTTP ${code})`;
+        : // Our own proxy answers these, not a mirror: 502 when every mirror
+          // failed at the network level, 503 from its local concurrency
+          // limiter before any mirror was asked. Neither is a refusal.
+          code === 502
+          ? 'Overpass mirrors unreachable'
+          : code === 503
+            ? 'Overpass temporarily unavailable'
+            : // A source is injected, so a caller's adapter may hand back a
+              // refusal with no status on it. "HTTP undefined" on a panel row is
+              // worse than not naming a number, so an unreadable code falls back
+              // to what `alpr` says when it cannot be more specific either.
+              code === null
+              ? 'Overpass temporarily unavailable'
+              : `Overpass refused the road query (HTTP ${code})`;
   return new RoadRequestError(message, { status: code });
 }
 

src/layers/traffic/source.test.mjs

@@ -207,6 +207,15 @@ test('an Overpass refusal is named by status, and keeps the status beside the wo
     'Overpass refused the road query (HTTP 500)',
   );
 
+  // 502 and 503 come from the local proxy (mirrors unreachable, local
+  // limiter busy), so they must not read as a mirror refusing the query.
+  assert.equal(roadRequestError(502).message, 'Overpass mirrors unreachable');
+  assert.equal(
+    roadRequestError(503).message,
+    'Overpass temporarily unavailable',
+  );
+  assert.equal(roadRequestError(503).status, 503);
+
   // An injected source may refuse without a readable code; a row must never
   // print "HTTP undefined" at a reader.
   for (const missing of [undefined, null, NaN, 'four-oh-six']) {