feat(gpu): "Retry errored jobs" — scoped requeue of errors only

After an agent-side fix (e.g. the short-video sampler), the errored jobs
(~2.8k) have exhausted their 3 attempts and stay parked: backfill skips
images that already have a job, and /reprocess is the nuclear option (it
resets the 179k DONE jobs too). There was no way to re-run just the errors.

POST /api/gpu/retry_errors resets every status='error' job (all task types)
to pending with attempts=0 and the stored error cleared — a small inline
UPDATE that returns {requeued: n} so the UI toast can show the count.

UI: a "Retry errored jobs" button on the GPU-agent card, right under the
queue tiles; disabled when errored==0. With the agent now logging ffmpeg's
stderr on failure, retrying also reveals which errors were real vs victims
of the fps-filter bug.

Test: retry_errors requeues the errored job (fresh attempts, error cleared)
and leaves done work untouched; asserts via column selects (Core-DML
gotcha), not ORM refresh.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/components/settings/GpuAgentCard.vue

@@ -52,6 +52,17 @@
       <div class="fc-q"><div class="fc-q__n" :class="queue.error ? 'fc-weak' : ''">{{ queue.error }}</div><div class="fc-q__l">errored</div></div>
     </div>
 
+    <v-btn
+      class="mt-3" color="accent" variant="tonal" rounded="pill" size="small"
+      prepend-icon="mdi-restart-alert" :loading="retrying"
+      :disabled="!queue.error" @click="onRetryErrors"
+    >Retry errored jobs</v-btn>
+    <p class="fc-muted text-caption mt-2 mb-0">
+      Errored jobs park after 3 failed attempts. This requeues just those (their
+      errors cleared, attempts reset) — use after updating the agent, without
+      re-running the whole done library.
+    </p>
+
     <v-btn
       class="mt-4" color="accent" variant="tonal" rounded="pill" size="small"
       prepend-icon="mdi-account-box-multiple" :loading="backfilling" @click="onBackfill"
@@ -164,6 +175,7 @@ const rotating = ref(false)
 const backfilling = ref(false)
 const backfillingSiglip = ref(false)
 const reprocessing = ref(false)
+const retrying = ref(false)
 const threshold = ref(0.85)
 const savingThreshold = ref(false)
 const autoApply = ref(true)
@@ -323,6 +335,19 @@ async function onBackfillSiglip() {
   }
 }
 
+async function onRetryErrors() {
+  retrying.value = true
+  try {
+    const { requeued } = await store.retryErrors()
+    toast({ text: `Requeued ${requeued} errored job${requeued === 1 ? '' : 's'} — run the agent to process them`, type: 'success' })
+    await refreshQueue()
+  } catch (e) {
+    toast({ text: `Could not retry errored jobs: ${e.message}`, type: 'error' })
+  } finally {
+    retrying.value = false
+  }
+}
+
 async function onReprocess() {
   if (!window.confirm('Re-process the ENTIRE library (re-detect + re-crop every image)? This is heavy and runs on the GPU agent.')) return
   reprocessing.value = true

frontend/src/stores/gpu.js

@@ -35,5 +35,11 @@ export const useGpuStore = defineStore('gpu', () => {
     return await api.post('/api/gpu/reprocess', { body: { task } })
   }
 
-  return { token, rotateToken, status, backfill, reprocess }
+  // Requeue ONLY the errored jobs (all task types) — the scoped recovery after
+  // an agent fix, without re-running the done library. Returns { requeued }.
+  async function retryErrors() {
+    return await api.post('/api/gpu/retry_errors')
+  }
+
+  return { token, rotateToken, status, backfill, reprocess, retryErrors }
 })