Close post-upload and admission race gaps

Treat fallback result fetch and body failures as uncertain Doodstream commits, and coordinate interval timing with slot acquisition so upload starts remain spaced without occupying another host's global slot during the wait.

tests/upload-manager-recovery-claims.test.js

@@ -749,8 +749,9 @@ test('upload interval is enforced at the admitted upload start', async () => {
   const hosterSettings = settings('byse.sx', 1);
   hosterSettings['byse.sx'].timeIntervalSec = 1;
   const manager = new UploadManager(hosterSettings);
-  manager._waitForInterval = async () => {
+  manager._waitForInterval = async (hoster, intervalMs, signal, acquireSlots) => {
     events.push('interval');
+    await acquireSlots();
   };
   const batch = runBatch(manager, [
     { jobId: 'interval-first', file: firstPath, hoster: 'byse.sx', accountId: 'BYSE_ACCOUNT', apiKey: 'BYSE_KEY' },
@@ -769,6 +770,61 @@ test('upload interval is enforced at the admitted upload start', async () => {
   assert.deepEqual(events.filter(event => event === 'interval'), ['interval', 'interval', 'interval']);
 });
 
+test('an interval wait never occupies the global slot of another hoster', async () => {
+  let markIntervalWaiting;
+  let releaseInterval;
+  let markOtherStarted;
+  const intervalWaiting = new Promise(resolve => {
+    markIntervalWaiting = resolve;
+  });
+  const intervalGate = new Promise(resolve => {
+    releaseInterval = resolve;
+  });
+  const otherStarted = new Promise(resolve => {
+    markOtherStarted = resolve;
+  });
+  loadManager(async (hoster) => {
+    if (hoster === 'voe.sx') markOtherStarted();
+    const code = hoster === 'voe.sx' ? 'VOEINTERVAL1' : 'BYSEINTERVAL1';
+    return {
+      file_code: code,
+      download_url: hoster === 'voe.sx' ? `https://voe.sx/${code}` : `https://byse.sx/d/${code}`,
+      embed_url: hoster === 'voe.sx' ? `https://voe.sx/e/${code}` : `https://byse.sx/e/${code}`
+    };
+  });
+  const hosterSettings = {
+    ...settings('byse.sx', 1),
+    ...settings('voe.sx', 1)
+  };
+  hosterSettings['byse.sx'].timeIntervalSec = 1;
+  const manager = new UploadManager(hosterSettings, { parallelUploadCount: 1 });
+  const originalWait = manager._waitForInterval.bind(manager);
+  manager._waitForInterval = async (hoster, intervalMs, signal, acquireSlots) => {
+    if (hoster === 'byse.sx') {
+      markIntervalWaiting();
+      await intervalGate;
+    }
+    return originalWait(hoster, 0, signal, acquireSlots);
+  };
+  const batch = runBatch(manager, [
+    { jobId: 'interval-waiting-hoster', file: firstPath, hoster: 'byse.sx', accountId: 'BYSE_ACCOUNT', apiKey: 'BYSE_KEY' },
+    { jobId: 'interval-independent-hoster', file: distinctPath, hoster: 'voe.sx', accountId: 'VOE_ACCOUNT', apiKey: 'VOE_KEY' }
+  ]);
+
+  await waitFor(intervalWaiting, 500, 'Configured interval did not start waiting');
+  let blockedError = null;
+  try {
+    await waitFor(otherStarted, 500, 'Interval wait occupied the global upload slot');
+  } catch (error) {
+    blockedError = error;
+  } finally {
+    releaseInterval();
+  }
+  const summary = await batch;
+  if (blockedError) throw blockedError;
+  assert.equal(summary.succeeded, 2);
+});
+
 for (const scenario of [
   {
     label: 'VOE',