fix(news): answer within the browser's wait on a first read

A country's first World News API read, or Liveuamap's, could take up to
20 s while the browser waits 15, so the panel showed the browser's own
"signal timed out". A read with nothing to serve yet is now waited for
at most 12 s, as GDELT's already was: past that the section answers
unavailable while the read goes on, and the next refresh is served from
it. A client timeout reads "News feed unavailable".

src/layers/news/source.js

@@ -161,13 +161,25 @@ export function createNewsSource({
     signal?.throwIfAborted();
     const timeout = AbortSignal.timeout(timeoutMs);
     const request = signal ? AbortSignal.any([signal, timeout]) : timeout;
-    const response = await fetchImpl(`${BASE_PATH}${path}`, {
-      signal: request,
-      cache: 'no-store',
-      redirect: 'error',
-    });
-    if (!response.ok) throw await responseError(response);
-    return readResponseJsonCapped(response, MAX_BYTES, request);
+    try {
+      const response = await fetchImpl(`${BASE_PATH}${path}`, {
+        signal: request,
+        cache: 'no-store',
+        redirect: 'error',
+      });
+      if (!response.ok) throw await responseError(response);
+      return await readResponseJsonCapped(response, MAX_BYTES, request);
+    } catch (cause) {
+      // Out of time the feed reads unavailable, not the browser's own words
+      // ("signal timed out"); the caller's own abort stays an abort.
+      if (timeout.aborted && !signal?.aborted)
+        throw Object.assign(new Error(msg('News feed unavailable')), {
+          code: 'timeout',
+          unavailable: false,
+          retryable: true,
+        });
+      throw cause;
+    }
   }
   return {
     // `hours` asks for counts over a shorter window than the server's own.

src/layers/news/source.test.mjs

@@ -176,7 +176,12 @@ test('reads time out and follow the caller signal', async () => {
       );
     });
   const slow = createNewsSource({ fetchImpl: hang, timeoutMs: 20 });
-  await assert.rejects(slow.getHotspots(), { name: 'TimeoutError' });
+  // Out of time it reads unavailable, in the app's words, and is retried.
+  await assert.rejects(slow.getHotspots(), {
+    message: 'News feed unavailable',
+    code: 'timeout',
+    retryable: true,
+  });
   const caller = new AbortController();
   const pending = createNewsSource({ fetchImpl: hang }).getFeed(
     {},