feat(ui): hover a suggestion → highlight the crop region it came from (#133 step 3)

The payoff: hover a suggestion in the rail and the exact crop that produced it
lights up on the image (a booru:head, a panel, a figure); a null-grounding tag
shows a subtle dashed whole-image frame ('global vector won, not a crop').
ImageCanvas gains a grounding overlay that tracks the <img>'s live bounding rect
(correct under object-fit letterboxing + pan/zoom) and draws the normalized bbox
+ a detector/kind label. SuggestionItem sets the hovered grounding via
provide/inject (no 4-level event relay through TagPanel/SuggestionsPanel/group);
ImageViewer AND ExploreView provide it + pass it to their canvas. Overlay is
pointer-events:none so it never blocks pan/zoom/click. Videos out of v1 scope.

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

frontend/src/components/modal/ImageCanvas.vue

@@ -16,20 +16,91 @@
         transform: `translate(${panZoom.state.x}px, ${panZoom.state.y}px) scale(${panZoom.state.scale})`
       }"
       draggable="false"
+      @load="onImgLoad"
     >
+    <!-- #1206 grounding overlay: tracks the <img>'s live rendered rect (so it's
+         correct under object-fit letterboxing + pan/zoom) and draws the crop
+         region a hovered suggestion came from. Null grounding → a subtle
+         whole-image frame ("the global vector won, not a crop"). -->
+    <div
+      v-if="hover && overlayBox"
+      class="fc-canvas__overlay"
+      :style="{
+        left: overlayBox.left + 'px', top: overlayBox.top + 'px',
+        width: overlayBox.width + 'px', height: overlayBox.height + 'px',
+      }"
+    >
+      <div
+        class="fc-canvas__region"
+        :class="{ 'fc-canvas__region--whole': !regionStyle }"
+        :style="regionStyle || {}"
+      >
+        <span class="fc-canvas__region-label">{{ regionLabel }}</span>
+      </div>
+    </div>
   </div>
 </template>
 
 <script setup>
-import { ref, watch } from 'vue'
+import { computed, nextTick, onMounted, onUnmounted, ref, watch } from 'vue'
 import { usePanZoom } from '../../composables/usePanZoom.js'
 
-const props = defineProps({ src: String, alt: String })
+const props = defineProps({
+  src: String,
+  alt: String,
+  // Hovered-suggestion grounding, or null when nothing is hovered:
+  //   null                        → no overlay
+  //   { g: {bbox,kind,detector} } → highlight that crop region
+  //   { g: null }                 → whole-image frame (not localized)
+  hover: { type: Object, default: null },
+})
 const emit = defineEmits(['close-request'])
 const panZoom = usePanZoom()
 
 const canvasEl = ref(null)
 const imgEl = ref(null)
+const overlayBox = ref(null)   // the <img>'s rect relative to the canvas
+
+// The <img> renders aspect-fit + transformed, so its getBoundingClientRect is
+// the ground truth for where the picture actually is. Position the overlay to
+// match it, then place the region as a % within.
+function measure () {
+  const img = imgEl.value
+  const canvas = canvasEl.value
+  if (!img || !canvas) { overlayBox.value = null; return }
+  const ir = img.getBoundingClientRect()
+  const cr = canvas.getBoundingClientRect()
+  if (!ir.width || !ir.height) { overlayBox.value = null; return }
+  overlayBox.value = {
+    left: ir.left - cr.left, top: ir.top - cr.top,
+    width: ir.width, height: ir.height,
+  }
+}
+
+const regionStyle = computed(() => {
+  const g = props.hover?.g
+  if (!g || !Array.isArray(g.bbox)) return null   // null grounding → whole frame
+  const [rx, ry, rw, rh] = g.bbox
+  return {
+    left: `${rx * 100}%`, top: `${ry * 100}%`,
+    width: `${rw * 100}%`, height: `${rh * 100}%`,
+  }
+})
+const regionLabel = computed(() => {
+  const g = props.hover?.g
+  return g ? (g.detector || g.kind || 'region') : 'whole image'
+})
+
+// Re-measure whenever hovering starts or the image could have moved.
+watch(() => props.hover, (h) => { if (h) nextTick(measure) })
+watch(
+  () => [panZoom.state.scale, panZoom.state.x, panZoom.state.y],
+  () => { if (props.hover) measure() },
+)
+function onResize () { if (props.hover) measure() }
+function onImgLoad () { if (props.hover) measure() }
+onMounted(() => window.addEventListener('resize', onResize))
+onUnmounted(() => window.removeEventListener('resize', onResize))
 
 // Reset zoom when the src changes (prev/next nav).
 watch(() => props.src, () => panZoom.reset())
@@ -79,4 +150,42 @@ function onCanvasClick(ev) {
   transition: transform 100ms ease-out;
   pointer-events: none;
 }
+
+/* Grounding overlay — never intercepts pan/zoom/click. */
+.fc-canvas__overlay {
+  position: absolute;
+  pointer-events: none;
+  z-index: 2;
+}
+.fc-canvas__region {
+  position: absolute;
+  border: 2px solid rgb(var(--v-theme-accent));
+  border-radius: 3px;
+  box-shadow: 0 0 0 9999px rgba(0, 0, 0, 0.28);   /* dim everything outside it */
+  transition: all 90ms ease-out;
+}
+/* Null grounding: a subtle full-image frame, no dimming — it says "this tag
+   came from the whole image, not a crop." */
+.fc-canvas__region--whole {
+  inset: 0;
+  border-style: dashed;
+  border-color: rgb(var(--v-theme-on-surface-variant));
+  box-shadow: none;
+}
+.fc-canvas__region-label {
+  position: absolute;
+  top: 0; left: 0;
+  transform: translateY(-100%);
+  font-size: 11px;
+  font-family: 'JetBrains Mono', monospace;
+  line-height: 1.4;
+  padding: 1px 6px;
+  white-space: nowrap;
+  background: rgb(var(--v-theme-accent));
+  color: rgb(var(--v-theme-on-surface));
+  border-radius: 3px 3px 0 0;
+}
+.fc-canvas__region--whole .fc-canvas__region-label {
+  background: rgb(var(--v-theme-on-surface-variant));
+}
 </style>

frontend/src/components/modal/ImageViewer.vue

@@ -60,6 +60,7 @@
           <template v-if="modal.current">
             <ImageCanvas
               v-if="!isVideo" :src="modal.current.image_url" :alt="`Image ${modal.current.id}`"
+              :hover="hoverGrounding"
               @close-request="$emit('close')"
             />
             <VideoCanvas
@@ -94,7 +95,7 @@
 </template>
 
 <script setup>
-import { computed, onMounted, onUnmounted, ref, watch } from 'vue'
+import { computed, onMounted, onUnmounted, provide, ref, watch } from 'vue'
 import { useModalStore } from '../../stores/modal.js'
 import { arrowNavAllowed, isTextEntry } from '../../utils/textEntry.js'
 import ImageCanvas from './ImageCanvas.vue'
@@ -110,6 +111,13 @@ const modal = useModalStore()
 const rootEl = ref(null)
 const showHelp = ref(false)
 
+// #1206: a deep descendant (SuggestionItem) sets this on hover to the crop that
+// produced a suggestion; ImageCanvas draws it over the image. provide/inject
+// avoids relaying a hover event through TagPanel → SuggestionsPanel → group.
+// null = nothing hovered; { g: grounding|null } = hovering (g null → whole-image).
+const hoverGrounding = ref(null)
+provide('fcSuggestionHover', hoverGrounding)
+
 const isVideo = computed(() =>
   modal.current?.mime && modal.current.mime.startsWith('video/')
 )

frontend/src/components/modal/SuggestionItem.vue

@@ -3,7 +3,10 @@
        name, score, and action buttons as one "object" (operator-asked
        2026-06-01). The row itself is informational; the green ✓ / red ✗
        verdict pair + 3-dot alias menu are the action affordances. -->
-  <div class="fc-suggestion" :class="{ 'fc-suggestion--rejected': suggestion.rejected }">
+  <div
+    class="fc-suggestion" :class="{ 'fc-suggestion--rejected': suggestion.rejected }"
+    @mouseenter="onEnter" @mouseleave="onLeave"
+  >
     <span class="fc-suggestion__name">
       {{ suggestion.display_name }}
       <span v-if="suggestion.rejected" class="fc-suggestion__rejected-tag"
@@ -72,12 +75,22 @@
 </template>
 
 <script setup>
-import { computed } from 'vue'
+import { computed, inject } from 'vue'
 import KebabMenu from '../common/KebabMenu.vue'
 
 const props = defineProps({ suggestion: { type: Object, required: true } })
 defineEmits(['accept', 'alias', 'remove-alias', 'dismiss', 'undismiss'])
 
+// #1206: on hover, tell the image viewer which crop produced this suggestion so
+// it highlights that region. Provided by ImageViewer/Explore; a no-op elsewhere.
+const hover = inject('fcSuggestionHover', null)
+function onEnter () {
+  if (hover) hover.value = { g: props.suggestion.grounding ?? null }
+}
+function onLeave () {
+  if (hover) hover.value = null
+}
+
 const scorePct = computed(() => `${Math.round(props.suggestion.score * 100)}%`)
 // Kebab now only carries alias actions: show it when this suggestion can be
 // aliased (raw model key, not yet aliased) or is already aliased (so it can be

frontend/src/views/ExploreView.vue

@@ -98,6 +98,7 @@
                 :key="store.anchor.id"
                 :src="store.anchor.image_url"
                 :alt="`Image ${store.anchor.id}`"
+                :hover="hoverGrounding"
               />
               <VideoCanvas
                 v-else
@@ -131,7 +132,7 @@
 </template>
 
 <script setup>
-import { computed, nextTick, onMounted, onUnmounted, ref, watch } from 'vue'
+import { computed, nextTick, onMounted, onUnmounted, provide, ref, watch } from 'vue'
 import { useRoute, useRouter } from 'vue-router'
 import { useApi } from '../composables/useApi.js'
 import { useExploreStore } from '../stores/explore.js'
@@ -152,6 +153,11 @@ const modal = useModalStore()
 
 const anchorId = computed(() => route.params.imageId || null)
 const isVideo = computed(() => !!store.anchor?.mime?.startsWith('video/'))
+
+// #1206: hovering a suggestion in the rail highlights the crop it came from on
+// the anchor image (same provide/inject as the modal viewer).
+const hoverGrounding = ref(null)
+provide('fcSuggestionHover', hoverGrounding)
 const seeding = ref(false)
 const seedError = ref(null)
 const tagPanelRef = ref(null)