feat(explore): Explore view + tag-gap closing + modal meta/download (#94b–d, #4a/b)

Cluster C frontend, milestone #94.

#94b Explore walk: new /explore/:imageId route + ExploreView + explore store.
Anchor (reuse /api/gallery/image), neighbour grid (reuse /api/gallery/similar,
24), click a neighbour to re-anchor; in-memory breadcrumb that trims on
backtrack (route is the source of truth). Empty/loading/error + no-embedding
states.

#94c tag-gap closing: components/explore/TagGapPanel — fetches
/api/images/cluster/tag-gaps for the anchor+neighbours, a consensus-threshold
slider (default 60%), per gap shows present/total + the missing thumbnails +
'Apply to N missing' → /api/tags/images/bulk/tags (source manual) → re-fetch.

#94d entry points: 'Explore' button in the modal RelatedStrip; the TopNav entry
comes free from the route's meta.title.

#4a metadata HUD + #4b split Download: new modal ImageMetaBar (always-on, above
ProvenancePanel) shows dimensions/size/type and a split Download button
(default Download, chevron → Copy link via utils/clipboard — no clipboard-image,
rule 95).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XCUHUGQLrBrkgyk1t49kpX

frontend/src/components/explore/TagGapPanel.vue

@@ -0,0 +1,159 @@
+<template>
+  <div class="fc-gaps">
+    <h3 class="fc-gaps__title">Tag-coverage gaps</h3>
+    <p class="fc-gaps__hint fc-muted">
+      Tags most of this cluster shares but some images lack. Apply to close the
+      gap across the stragglers.
+    </p>
+
+    <div class="fc-gaps__threshold">
+      <label class="text-caption fc-muted">
+        Consensus ≥ {{ Math.round(threshold * 100) }}%
+      </label>
+      <v-slider
+        v-model="threshold"
+        :min="0.3" :max="0.95" :step="0.05"
+        density="compact" hide-details color="accent"
+        aria-label="Consensus threshold"
+        @update:model-value="onThresholdInput"
+      />
+    </div>
+
+    <div v-if="loading" class="fc-gaps__state">
+      <v-progress-circular indeterminate size="22" width="2" color="accent" />
+    </div>
+    <v-alert v-else-if="error" type="error" variant="tonal" density="compact" class="mt-2">
+      {{ error }}
+    </v-alert>
+    <p v-else-if="!store.clusterIds.length" class="fc-gaps__state fc-muted text-body-2">
+      Anchor on an image with visual neighbours to see gaps.
+    </p>
+    <p v-else-if="!gaps.length" class="fc-gaps__state fc-muted text-body-2">
+      No gaps at this threshold — this cluster is consistently tagged.
+    </p>
+
+    <div v-else class="fc-gaps__list">
+      <div v-for="g in gaps" :key="g.tag_id" class="fc-gap">
+        <div class="fc-gap__head">
+          <span class="fc-gap__name">{{ g.name }}</span>
+          <span class="fc-gap__count fc-muted" :title="`${g.present_count} of ${g.total} images have this tag`">
+            {{ g.present_count }}/{{ g.total }}
+          </span>
+        </div>
+        <div class="fc-gap__missing">
+          <img
+            v-for="iid in g.missing_image_ids.slice(0, MISSING_PREVIEW)" :key="iid"
+            :src="store.thumbById[iid]" alt="" loading="lazy"
+          />
+          <span
+            v-if="g.missing_image_ids.length > MISSING_PREVIEW"
+            class="fc-muted text-caption"
+          >+{{ g.missing_image_ids.length - MISSING_PREVIEW }}</span>
+        </div>
+        <v-btn
+          size="small" color="accent" variant="tonal" rounded="pill"
+          :loading="applyingId === g.tag_id"
+          prepend-icon="mdi-tag-plus"
+          @click="applyGap(g)"
+        >Apply to {{ g.missing_image_ids.length }} missing</v-btn>
+      </div>
+    </div>
+  </div>
+</template>
+
+<script setup>
+import { ref, watch } from 'vue'
+import { useExploreStore } from '../../stores/explore.js'
+import { useApi } from '../../composables/useApi.js'
+import { useInflightToken } from '../../composables/useInflightToken.js'
+import { toast } from '../../utils/toast.js'
+
+const MISSING_PREVIEW = 8
+
+const store = useExploreStore()
+const api = useApi()
+
+const threshold = ref(0.6)
+const gaps = ref([])
+const loading = ref(false)
+const error = ref(null)
+const applyingId = ref(null)
+
+const inflight = useInflightToken()
+let debounce = null
+
+async function fetchGaps () {
+  const ids = store.clusterIds
+  if (ids.length < 2) { gaps.value = []; return }
+  inflight.cancel()
+  const t = inflight.claim()
+  loading.value = true
+  error.value = null
+  try {
+    const body = await api.post('/api/images/cluster/tag-gaps', {
+      body: { image_ids: ids, threshold: threshold.value },
+    })
+    if (!t.isCurrent()) return
+    gaps.value = body.gaps || []
+  } catch (e) {
+    if (t.isCurrent()) { error.value = e.message; gaps.value = [] }
+  } finally {
+    if (t.isCurrent()) loading.value = false
+  }
+}
+
+function onThresholdInput () {
+  if (debounce) clearTimeout(debounce)
+  debounce = setTimeout(fetchGaps, 350)
+}
+
+// Re-evaluate gaps whenever the cluster changes (new anchor / new neighbours).
+watch(() => store.clusterIds.join(','), fetchGaps, { immediate: true })
+
+async function applyGap (g) {
+  applyingId.value = g.tag_id
+  try {
+    const res = await api.post('/api/tags/images/bulk/tags', {
+      body: { image_ids: g.missing_image_ids, tag_id: g.tag_id, source: 'manual' },
+    })
+    toast({
+      text: `Applied “${g.name}” to ${res.added_count ?? g.missing_image_ids.length} image(s)`,
+      type: 'success',
+    })
+    await fetchGaps()   // the gap shrinks/closes — refresh
+  } catch (e) {
+    toast({ text: `Couldn't apply “${g.name}”: ${e.message}`, type: 'error' })
+  } finally {
+    applyingId.value = null
+  }
+}
+</script>
+
+<style scoped>
+.fc-muted { color: rgb(var(--v-theme-on-surface-variant)); }
+.fc-gaps {
+  padding: 14px; border-radius: 12px;
+  background: rgba(var(--v-theme-on-surface), 0.03);
+  border: 1px solid rgba(var(--v-theme-on-surface), 0.10);
+}
+.fc-gaps__title {
+  font-family: 'Fraunces', Georgia, serif; font-size: 16px; font-weight: 500;
+  margin-bottom: 4px;
+}
+.fc-gaps__hint { font-size: 12px; margin-bottom: 10px; }
+.fc-gaps__threshold { margin-bottom: 8px; }
+.fc-gaps__state { display: flex; justify-content: center; padding: 20px 0; }
+.fc-gaps__list { display: flex; flex-direction: column; gap: 12px; }
+.fc-gap {
+  padding: 10px; border-radius: 10px;
+  background: rgba(var(--v-theme-on-surface), 0.04);
+}
+.fc-gap__head { display: flex; justify-content: space-between; align-items: baseline; margin-bottom: 6px; }
+.fc-gap__name { font-weight: 600; }
+.fc-gap__count { font-variant-numeric: tabular-nums; font-size: 12px; }
+.fc-gap__missing { display: flex; align-items: center; gap: 4px; flex-wrap: wrap; margin-bottom: 8px; }
+.fc-gap__missing img {
+  width: 36px; height: 36px; object-fit: cover; border-radius: 5px;
+  background: rgb(var(--v-theme-surface-light));
+}
+</style>

frontend/src/components/modal/ImageMetaBar.vue

@@ -0,0 +1,96 @@
+<template>
+  <section v-if="img" class="fc-meta" aria-label="Image details">
+    <!-- #4a: dimensions / size / type — already on the payload, shown nowhere
+         until now. -->
+    <dl class="fc-meta__grid">
+      <div v-if="img.width && img.height" class="fc-meta__item">
+        <dt>Dimensions</dt><dd>{{ img.width }} × {{ img.height }}</dd>
+      </div>
+      <div v-if="img.size_bytes" class="fc-meta__item">
+        <dt>Size</dt><dd>{{ humanSize(img.size_bytes) }}</dd>
+      </div>
+      <div v-if="img.mime" class="fc-meta__item">
+        <dt>Type</dt><dd>{{ shortType(img.mime) }}</dd>
+      </div>
+    </dl>
+
+    <!-- #4b: split Download — default Download, chevron → Copy link. Image-to-
+         clipboard is OFF the table on the plain-HTTP origin (rule 95), so the
+         secondary action copies the link TEXT, which works everywhere. -->
+    <v-btn-group divided density="comfortable" variant="tonal" color="accent" rounded="pill">
+      <v-btn prepend-icon="mdi-download" @click="download">Download</v-btn>
+      <v-menu location="bottom end">
+        <template #activator="{ props }">
+          <v-btn v-bind="props" icon="mdi-chevron-down" aria-label="More download options" />
+        </template>
+        <v-list density="compact">
+          <v-list-item prepend-icon="mdi-link-variant" title="Copy link" @click="copyLink" />
+          <v-list-item prepend-icon="mdi-download" title="Download" @click="download" />
+        </v-list>
+      </v-menu>
+    </v-btn-group>
+  </section>
+</template>
+
+<script setup>
+import { computed } from 'vue'
+import { useModalStore } from '../../stores/modal.js'
+import { copyText } from '../../utils/clipboard.js'
+import { toast } from '../../utils/toast.js'
+
+const modal = useModalStore()
+const img = computed(() => modal.current)
+
+function humanSize (bytes) {
+  const units = ['B', 'KB', 'MB', 'GB']
+  let n = bytes
+  let i = 0
+  while (n >= 1024 && i < units.length - 1) { n /= 1024; i++ }
+  return `${n < 10 && i > 0 ? n.toFixed(1) : Math.round(n)} ${units[i]}`
+}
+function shortType (mime) { return mime.split('/')[1]?.toUpperCase() || mime }
+
+function absoluteUrl () {
+  const origin = typeof window !== 'undefined' ? window.location.origin : ''
+  return origin + img.value.image_url
+}
+
+function download () {
+  // Same-origin /images/* link — the download attribute lets the browser save
+  // the original (filename derived from the path) instead of navigating to it.
+  const a = document.createElement('a')
+  a.href = img.value.image_url
+  a.setAttribute('download', '')
+  document.body.appendChild(a)
+  a.click()
+  a.remove()
+}
+
+async function copyLink () {
+  try {
+    await copyText(absoluteUrl())
+    toast({ text: 'Link copied to clipboard', type: 'success' })
+  } catch {
+    toast({ text: 'Could not copy the link', type: 'error' })
+  }
+}
+</script>
+
+<style scoped>
+.fc-meta {
+  padding: 14px 16px 0;
+  display: flex; flex-direction: column; gap: 10px;
+}
+.fc-meta__grid {
+  display: flex; flex-wrap: wrap; gap: 4px 18px; margin: 0;
+}
+.fc-meta__item { display: flex; flex-direction: column; }
+.fc-meta__item dt {
+  font-size: 10px; text-transform: uppercase; letter-spacing: 0.06em;
+  color: rgb(var(--v-theme-on-surface-variant));
+}
+.fc-meta__item dd {
+  margin: 0; font-size: 13px; font-variant-numeric: tabular-nums;
+  color: rgb(var(--v-theme-on-surface));
+}
+</style>

frontend/src/components/modal/ImageViewer.vue

@@ -73,6 +73,7 @@
         </div>
 
         <aside v-if="modal.current" class="fc-viewer__side">
+          <ImageMetaBar />
           <ProvenancePanel />
           <TagPanel />
           <!-- Non-blocking: fetches its own similar set after the modal is up;
@@ -90,6 +91,7 @@ import { useModalStore } from '../../stores/modal.js'
 import { arrowNavAllowed, isTextEntry } from '../../utils/textEntry.js'
 import ImageCanvas from './ImageCanvas.vue'
 import VideoCanvas from './VideoCanvas.vue'
+import ImageMetaBar from './ImageMetaBar.vue'
 import TagPanel from './TagPanel.vue'
 import ProvenancePanel from './ProvenancePanel.vue'
 import RelatedStrip from './RelatedStrip.vue'

frontend/src/components/modal/RelatedStrip.vue

@@ -5,11 +5,18 @@
   <div v-if="show" class="fc-related">
     <div class="fc-related__head">
       <span class="fc-related__title">Related</span>
-      <v-btn
-        size="x-small" variant="text" color="accent"
-        :disabled="loading || !results.length"
-        @click="seeAll"
-      >See all similar</v-btn>
+      <div class="fc-related__actions">
+        <v-btn
+          size="x-small" variant="text" color="accent"
+          prepend-icon="mdi-compass-outline"
+          @click="explore"
+        >Explore</v-btn>
+        <v-btn
+          size="x-small" variant="text" color="accent"
+          :disabled="loading || !results.length"
+          @click="seeAll"
+        >See all similar</v-btn>
+      </div>
     </div>
     <div class="fc-related__row">
       <template v-if="loading">
@@ -94,6 +101,14 @@ function seeAll() {
   modal.close()
   router.push({ name: 'gallery', query: { similar_to: String(id) } })
 }
+
+// #94: leave the modal and open the dedicated Explore walk anchored here.
+function explore() {
+  const id = modal.current?.id
+  if (!id) return
+  modal.close()
+  router.push({ name: 'explore', params: { imageId: String(id) } })
+}
 </script>
 
 <style scoped>
@@ -105,6 +120,7 @@ function seeAll() {
   display: flex; align-items: center; justify-content: space-between;
   margin-bottom: 8px;
 }
+.fc-related__actions { display: flex; align-items: center; gap: 2px; }
 .fc-related__title {
   font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.06em;
   color: rgb(var(--v-theme-on-surface-variant));