fix(ui): tag autocomplete no longer shows stale wrong-prefix results (race)

The keystroke debounce cleared the timer but not an already-fired fetch, so a
slower earlier-prefix response ("s") could land after "sex" and overwrite the
dropdown with wrong-prefix matches (operator-flagged with a "sex"→Stockings/
Super Mario screenshot). Gate each autocomplete response on a useInflightToken
(cancel on every keystroke, isCurrent() after the await) so only the latest
query's results are applied.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

frontend/src/components/modal/TagAutocomplete.vue

@@ -97,6 +97,7 @@
 import { computed, nextTick, onMounted, ref, watch } from 'vue'
 import { useTagStore } from '../../stores/tags.js'
 import { useSuggestionsStore } from '../../stores/suggestions.js'
+import { useInflightToken } from '../../composables/useInflightToken.js'
 import FandomPicker from './FandomPicker.vue'
 
 const emit = defineEmits(['pick-existing', 'pick-new', 'accept-suggestion', 'cancel'])
@@ -183,17 +184,26 @@ const parsed = computed(() => {
 const parsedKind = computed(() => parsed.value.kind)
 const parsedName = computed(() => parsed.value.name)
 
+// Inflight guard: the debounce only clears the TIMER, so once a fetch has fired
+// it still races later ones — a slower earlier-prefix response ("s") could land
+// after "sex" and overwrite the dropdown with stale, wrong-prefix matches
+// (operator-flagged 2026-07-06). Gate each response on a token so only the latest
+// query's results are applied.
+const acInflight = useInflightToken()
 let debounceId = null
 watch(query, () => {
   highlight.value = 0
   if (debounceId) clearTimeout(debounceId)
+  acInflight.cancel()
   debounceId = setTimeout(async () => {
     const q = parsedName.value
     if (!q) { hits.value = []; return }
     // Autocomplete across ALL kinds. When the user typed a prefix the
     // matches list is naturally narrower because the parsed name is
     // shorter; we don't filter server-side by kind.
-    hits.value = await store.autocomplete(q, null, 10)
+    const t = acInflight.claim()
+    const res = await store.autocomplete(q, null, 10)
+    if (t.isCurrent()) hits.value = res
   }, 200)
 })