fix(modal): next arrow clears metadata panel + arrows work in empty tag input

Image viewer (#609):
- The next (▶) arrow was offset from the viewport edge (right:16px) so it
  floated over the 320px metadata side panel. Offset it off a shared
  --fc-side-w var so it sits at the image's right edge instead; full-width
  again below 900px when the panel stacks under the image.
- Arrow nav was fully disabled whenever a text field was focused. Now it
  yields to the caret ONLY when the field has text; an empty tag-entry field
  still navigates ←/→. Extracted to utils/textEntry.js (arrowNavAllowed).
  ESC behaviour unchanged (already closes the modal, overlay-aware).

Test: arrowNavAllowed — empty/non-text → navigate, text present → don't.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/components/modal/ImageViewer.vue

@@ -60,6 +60,7 @@
 <script setup>
 import { computed, onMounted, onUnmounted, ref, watch } from 'vue'
 import { useModalStore } from '../../stores/modal.js'
+import { arrowNavAllowed } from '../../utils/textEntry.js'
 import ImageCanvas from './ImageCanvas.vue'
 import VideoCanvas from './VideoCanvas.vue'
 import TagPanel from './TagPanel.vue'
@@ -105,11 +106,13 @@ function onKeyDown(ev) {
     ev.preventDefault()
     emit('close')
   } else if (ev.key === 'ArrowLeft') {
-    if (isTextEntry(ev.target)) return
+    // Navigate unless the caret is in a non-empty text field (then let it move
+    // through the text). An empty tag-entry field still navigates.
+    if (!arrowNavAllowed(ev.target)) return
     ev.preventDefault()
     modal.goPrev()
   } else if (ev.key === 'ArrowRight') {
-    if (isTextEntry(ev.target)) return
+    if (!arrowNavAllowed(ev.target)) return
     ev.preventDefault()
     modal.goNext()
   }
@@ -135,17 +138,14 @@ watch(() => modal.currentImageId, async () => {
 function nextFrame() {
   return new Promise(resolve => requestAnimationFrame(resolve))
 }
-
-function isTextEntry(el) {
-  if (!el) return false
-  const tag = el.tagName
-  return tag === 'INPUT' || tag === 'TEXTAREA' || el.isContentEditable
-}
 </script>
 
 <style scoped>
 .fc-viewer {
   position: fixed; inset: 0; z-index: 2000;
+  /* Single source of truth for the metadata side-panel width — the next
+     arrow offsets off it so it never overlaps the panel. */
+  --fc-side-w: 320px;
   /* Obsidian haze (#14171A = 20,23,26) — same palette as TopNav,
      mid-opacity + blur so the page behind shows through faintly. */
   background: rgba(20, 23, 26, 0.65);
@@ -174,7 +174,12 @@ function isTextEntry(el) {
   position: absolute; top: 72px; right: 16px; z-index: 3;
 }
 .fc-viewer__nav--prev { left: 16px; transform: translateY(-50%); }
-.fc-viewer__nav--next { right: 16px; transform: translateY(-50%); }
+/* Sit just inside the image area, clear of the metadata side panel —
+   not floating over it (operator-flagged 2026-06-04). */
+.fc-viewer__nav--next {
+  right: calc(var(--fc-side-w) + 16px);
+  transform: translateY(-50%);
+}
 .fc-viewer__body {
   flex: 1; display: flex; min-height: 0;
 }
@@ -187,7 +192,7 @@ function isTextEntry(el) {
   min-width: 0; min-height: 0;
 }
 .fc-viewer__side {
-  width: 320px; flex-shrink: 0;
+  width: var(--fc-side-w); flex-shrink: 0;
   background: rgb(var(--v-theme-surface));
   border-left: 1px solid rgb(var(--v-theme-surface-light));
   overflow-y: auto;
@@ -195,6 +200,8 @@ function isTextEntry(el) {
 
 @media (max-width: 900px) {
   .fc-viewer__body { flex-direction: column; }
+  /* Side panel drops below the image — the next arrow uses the full width. */
+  .fc-viewer__nav--next { right: 16px; }
   .fc-viewer__side {
     width: 100%;
     max-height: 40vh;

frontend/src/utils/textEntry.js

@@ -0,0 +1,21 @@
+// Helpers for deciding whether a keyboard shortcut should fire or yield to a
+// focused text field.
+
+export function isTextEntry (el) {
+  if (!el) return false
+  const tag = el.tagName
+  return tag === 'INPUT' || tag === 'TEXTAREA' || el.isContentEditable
+}
+
+export function hasText (el) {
+  if (!el) return false
+  if (el.isContentEditable) return (el.textContent || '').length > 0
+  return (el.value || '').length > 0
+}
+
+// Prev/next arrow navigation should fire UNLESS focus is in a text entry that
+// already has content — in that case the arrows belong to the caret so it can
+// move through the text. An empty (or non-text) target still navigates.
+export function arrowNavAllowed (target) {
+  return !(isTextEntry(target) && hasText(target))
+}

frontend/test/textEntry.spec.js

@@ -0,0 +1,31 @@
+// @vitest-environment happy-dom
+import { describe, it, expect } from 'vitest'
+
+import { arrowNavAllowed, hasText, isTextEntry } from '../src/utils/textEntry.js'
+
+describe('textEntry helpers', () => {
+  it('navigates when the target is not a text field', () => {
+    expect(arrowNavAllowed(document.createElement('div'))).toBe(true)
+    expect(arrowNavAllowed(null)).toBe(true)
+  })
+
+  it('navigates when a focused tag input is empty', () => {
+    const input = document.createElement('input')
+    input.value = ''
+    expect(arrowNavAllowed(input)).toBe(true)
+  })
+
+  it('does NOT navigate when the input has text (caret moves instead)', () => {
+    const input = document.createElement('input')
+    input.value = 'naruto'
+    expect(arrowNavAllowed(input)).toBe(false)
+  })
+
+  it('isTextEntry / hasText recognise inputs and textareas', () => {
+    const ta = document.createElement('textarea')
+    ta.value = 'x'
+    expect(isTextEntry(ta)).toBe(true)
+    expect(hasText(ta)).toBe(true)
+    expect(isTextEntry(document.createElement('div'))).toBe(false)
+  })
+})