feat(import): /api/import/clear-stuck endpoint + Clear stuck UI button — escape hatch for the autoretry-loop case the automatic sweep can't break

Operator hit 3 large PNGs stuck in 'processing' for 2 days 2026-05-25:
the existing recover_interrupted_tasks flips processing > 5min back to
queued + .delay(), but if the underlying file is unfixably broken (e.g.,
PIL OSError, also patched in 68cffce), the loop never terminates and the
'Scanning...' banner sticks at 0/0 forever blocking new scans.

/api/import/clear-stuck:
- Flips every task in pending/queued/processing to 'failed' with a clear
  marker error message
- Finalizes any 'running' ImportBatch that has no remaining active children
- Idempotent + non-destructive: rows survive, can be retried once the
  underlying cause is resolved

UI button 'Clear stuck...' sits next to 'Retry failed' / 'Clear completed'
with a warning-tonal alert in the confirm dialog explaining what it does
and recommending Retry failed once the cause is fixed.

Tests: clears mixed non-terminal states, untouches complete rows,
finalizes orphan batch, no-op when nothing stuck.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/settings/ImportTaskList.vue

@@ -17,6 +17,12 @@
       >
         Retry failed
       </v-btn>
+      <v-btn
+        variant="text" rounded="pill" size="small" color="warning"
+        :disabled="!hasStuck" @click="onClearStuckOpen"
+      >
+        Clear stuck…
+      </v-btn>
       <v-btn
         variant="text" rounded="pill" size="small" color="error"
         @click="onClearOpen"
@@ -69,6 +75,31 @@
         </v-card-actions>
       </v-card>
     </v-dialog>
+
+    <v-dialog v-model="clearStuckDialog" max-width="480">
+      <v-card>
+        <v-card-title>Clear stuck tasks</v-card-title>
+        <v-card-text>
+          <v-alert type="warning" variant="tonal" density="compact" class="mb-3">
+            Force every <strong>pending / queued / processing</strong> task to
+            <strong>failed</strong> and finalize any active batch that
+            has no remaining work. Use this when the automatic recovery
+            sweep keeps re-queueing the same row (e.g., corrupt file in
+            an autoretry loop, or worker model missing).
+          </v-alert>
+          <p class="text-body-2">
+            Tasks remain in the database with status=<code>failed</code>;
+            click <em>Retry failed</em> once the underlying cause is
+            resolved to re-queue them.
+          </p>
+        </v-card-text>
+        <v-card-actions>
+          <v-spacer />
+          <v-btn @click="clearStuckDialog = false">Cancel</v-btn>
+          <v-btn color="warning" rounded="pill" @click="onClearStuckConfirm">Clear stuck</v-btn>
+        </v-card-actions>
+      </v-card>
+    </v-dialog>
   </v-card>
 </template>
 
@@ -80,6 +111,7 @@ const store = useImportStore()
 const statusFilter = ref(null)
 const clearDialog = ref(false)
 const clearAgeDays = ref(7)
+const clearStuckDialog = ref(false)
 
 const statusOptions = [
   { title: 'All', value: null },
@@ -100,6 +132,9 @@ const headers = [
 ]
 
 const hasFailed = computed(() => store.tasks.some(t => t.status === 'failed'))
+const hasStuck = computed(() => store.tasks.some(
+  t => t.status === 'pending' || t.status === 'queued' || t.status === 'processing'
+))
 
 function statusColor(s) {
   return {
@@ -138,4 +173,9 @@ async function onClearConfirm() {
   await store.clearCompleted(clearAgeDays.value)
   clearDialog.value = false
 }
+function onClearStuckOpen() { clearStuckDialog.value = true }
+async function onClearStuckConfirm() {
+  await store.clearStuck()
+  clearStuckDialog.value = false
+}
 </script>

frontend/src/stores/import.js

@@ -92,6 +92,13 @@ export const useImportStore = defineStore('import', () => {
     await loadTasks(true)
   }
 
+  async function clearStuck() {
+    const body = await api.post('/api/import/clear-stuck')
+    await loadTasks(true)
+    await refreshStatus()
+    return body
+  }
+
   const hasMore = computed(() => tasksNextCursor.value !== null)
 
   return {
@@ -101,6 +108,6 @@ export const useImportStore = defineStore('import', () => {
     triggerError,
     loadSettings, patchSettings,
     refreshStatus, triggerScan,
-    loadTasks, setStatusFilter, retryFailed, clearCompleted
+    loadTasks, setStatusFilter, retryFailed, clearCompleted, clearStuck
   }
 })