diff --git a/ui/src/features/scene3d/Scene3DWorkspace.tsx b/ui/src/features/scene3d/Scene3DWorkspace.tsx
index 46937276..3beddba3 100644
--- a/ui/src/features/scene3d/Scene3DWorkspace.tsx
+++ b/ui/src/features/scene3d/Scene3DWorkspace.tsx
@@ -1,6 +1,6 @@
 import { useEffect, useMemo, useRef, useState } from 'react'
 import { fetchOutputs, type ApiOutput } from '../../api/client'
-import { AssetExplorerDialog } from '../../components/common/AssetExplorerDialog'
+import { AssetInput } from '../../features/asset-picker/AssetInput.tsx'
 import { useUiTranslation } from '../../i18n'
 import { useStore } from '../../stores/useStore'
 import { cameraEyeAtTime, projectPoint } from './camera.ts'
@@ -11,6 +11,7 @@ import { canMutateWorld3DScene } from './exportLock.ts'
 import { exportWorld3DDocument } from './exportFlow.ts'
 import { Scene3DStage, type Scene3DStageHandle } from './Scene3DStage.tsx'
 import { applyScene3DTemplate, patchScene3DSlot, SCENE3D_TEMPLATES, type Scene3DTemplateId } from './templates.ts'
+import { commitSlotSourceChoice, pickerOutputFromSlot, type SlotSourceCapture } from './slotSource.ts'
 import type { Scene3DCameraFamily, Scene3DClipCatalogEntry, Scene3DDocument, Scene3DLoop, Scene3DSlot } from './types.ts'
 import { documentFromWorld3DRequest, listenForWorld3DWorkflow } from './world3dAgent.ts'
 
@@ -54,11 +55,13 @@ export function Scene3DWorkspace({ width, height }: Props) {
   const sceneDocRef = useRef(sceneDoc)
   const dragRef = useRef<{ id: string; startX: number; startZ: number; pointerX: number; pointerY: number } | null>(null)
   const [catalogs, setCatalogs] = useState<Record<string, Scene3DClipCatalogEntry[]>>({})
-  const [explorerSlot, setExplorerSlot] = useState<string | null>(null)
-  const [explorerItems, setExplorerItems] = useState<ApiOutput[]>([])
+  const [modelItems, setModelItems] = useState<ApiOutput[]>([])
+  const [imageItems, setImageItems] = useState<ApiOutput[]>([])
   const [exporting, setExporting] = useState(false)
   const [exportNote, setExportNote] = useState<string | null>(null)
   const exportingRef = useRef(false)
+  const generationRef = useRef(0)
+  const workspaceRef = useRef('')
   const stageRef = useRef<Scene3DStageHandle>(null)
   const workspace = useStore(s => s.activeWorkspace)
   const fps = sceneDoc.fps
@@ -94,6 +97,7 @@ export function Scene3DWorkspace({ width, height }: Props) {
       throw new Error('world3d-export-in-progress')
     }
     const next = documentFromWorld3DRequest(request)
+    generationRef.current += 1
     setSceneDoc(next)
     setFrame(0)
     return { message: next.templateId, templateId: request.templateId, slotIds: next.slots.map(slot => slot.id) }
@@ -125,28 +129,62 @@ export function Scene3DWorkspace({ width, height }: Props) {
     return () => cancelAnimationFrame(raf)
   }, [playing, sceneDoc.duration, fps, count])
 
-  const assignSource = (slotId: string, url: string, media: Scene3DSlot['media'] = 'model3d') => {
+  useEffect(() => {
+    if (workspaceRef.current && workspaceRef.current !== workspace) generationRef.current += 1
+    workspaceRef.current = workspace
+  }, [workspace])
+
+  useEffect(() => {
+    let alive = true
+    Promise.all([
+      fetchOutputs(200, 0, { mediaType: 'model3d', workspace }),
+      fetchOutputs(200, 0, { mediaType: 'image', workspace }),
+    ]).then(([models, images]) => {
+      if (!alive) return
+      setModelItems(models.outputs.filter(item => item.type === 'model3d' && /\.glb$/i.test(item.name)))
+      setImageItems(images.outputs.filter(item => item.type === 'image'))
+    }).catch(() => {
+      if (!alive) return
+      setModelItems([])
+      setImageItems([])
+    })
+    return () => { alive = false }
+  }, [workspace])
+
+  const assignChoice = (slot: Scene3DSlot, capture: SlotSourceCapture, item: ApiOutput | null) => {
+    const commit = commitSlotSourceChoice({
+      generation: generationRef.current,
+      slotId: slot.id,
+      templateId: sceneDocRef.current.templateId,
+      workspaceId: workspaceRef.current || workspace,
+      exporting: exportingRef.current,
+    }, capture, item)
+    if (commit.action === 'ignore') return
     if (!canMutateWorld3DScene(exportingRef.current)) return
-    setSceneDoc(current => patchScene3DSlot(current, slotId, { sourceUrl: url, media, clip: null }))
+    if (commit.action === 'clear') {
+      revokeIfBlob(slot.sourceUrl)
+      setSceneDoc(current => patchScene3DSlot(current, slot.id, { sourceUrl: '', sourceRef: undefined, clip: null }))
+      setCatalogs(current => {
+        const next = { ...current }
+        delete next[slot.id]
+        return next
+      })
+      return
+    }
+    revokeIfBlob(slot.sourceUrl)
+    setSceneDoc(current => patchScene3DSlot(current, slot.id, {
+      sourceUrl: commit.sourceUrl,
+      sourceRef: commit.sourceRef,
+      media: commit.media,
+      clip: commit.clip,
+    }))
     setCatalogs(current => {
       const next = { ...current }
-      delete next[slotId]
+      delete next[slot.id]
       return next
     })
   }
 
-  const openExplorer = async (slot: Scene3DSlot) => {
-    if (!canMutateWorld3DScene(exportingRef.current)) return
-    setExplorerSlot(slot.id)
-    try {
-      const kind = slot.slot === 'background' ? 'image' : 'model3d'
-      const data = await fetchOutputs(0, 0, { mediaType: kind, workspace })
-      setExplorerItems(kind === 'model3d' ? data.outputs.filter(item => /\.glb$/i.test(item.name)) : data.outputs)
-    } catch {
-      setExplorerItems([])
-    }
-  }
-
   const applyScene = (updater: Parameters<typeof setSceneDoc>[0]) => {
     if (!canMutateWorld3DScene(exportingRef.current)) return
     setSceneDoc(updater)
@@ -154,6 +192,7 @@ export function Scene3DWorkspace({ width, height }: Props) {
 
   const mountTemplate = (id: Scene3DTemplateId) => {
     if (!canMutateWorld3DScene(exportingRef.current)) return
+    generationRef.current += 1
     for (const slot of sceneDoc.slots) revokeIfBlob(slot.sourceUrl)
     applyScene(applyScene3DTemplate(id))
     setCatalogs({})
@@ -183,7 +222,6 @@ export function Scene3DWorkspace({ width, height }: Props) {
     const stage = stageRef.current
     if (!stage || exportingRef.current || playing) return
     dragRef.current = null
-    setExplorerSlot(null)
     setExportingFlag(true)
     setExportNote(t('stage.exporting'))
     try {
@@ -289,24 +327,32 @@ export function Scene3DWorkspace({ width, height }: Props) {
       <div className="grid gap-1.5 md:grid-cols-2">
         {sceneDoc.slots.map(slot => {
           const clips = catalogs[slot.id] ?? []
+          const capture: SlotSourceCapture = {
+            generation: generationRef.current,
+            slotId: slot.id,
+            templateId: sceneDoc.templateId,
+            workspaceId: workspace,
+          }
           return (
             <div key={slot.id} className={`rounded border p-1.5 text-[9px] text-text-secondary ${selectedId === slot.id ? 'border-cyan-300 bg-cyan-400/5' : 'border-border bg-bg-primary'}`}>
               <button type="button" className="block font-medium text-text-primary" onClick={() => setSelectedId(slot.id)}>{t(`stage.slot.${slot.slot}`)}</button>
-              <button type="button" disabled={exporting} onClick={() => void openExplorer(slot)} className="mt-1 w-full rounded border border-cyan-400/40 bg-cyan-400/10 px-1.5 py-1 text-[9px] text-cyan-100 disabled:opacity-40">
-                {t('stage.fromApp')}
-              </button>
-              <input
-                type="file"
-                disabled={exporting}
-                accept={slot.slot === 'background' ? 'image/*' : '.glb,model/gltf-binary'}
-                className="mt-1 w-full text-[8px] disabled:opacity-40"
-                onChange={event => {
-                  const file = event.target.files?.[0]
-                  if (!file) return
-                  revokeIfBlob(slot.sourceUrl)
-                  assignSource(slot.id, URL.createObjectURL(file), slot.slot === 'background' ? 'image' : 'model3d')
-                }}
-              />
+              <div className="mt-1">
+                <AssetInput
+                  label={t(`stage.slot.${slot.slot}`)}
+                  placeholder={t('stage.fromApp')}
+                  items={slot.slot === 'background' ? imageItems : modelItems}
+                  value={pickerOutputFromSlot(slot.sourceUrl, slot.media, slot.sourceRef)}
+                  accept={slot.slot === 'background' ? 'image/*' : '.glb,model/gltf-binary'}
+                  optional
+                  disabled={exporting}
+                  constraints={{
+                    kinds: slot.slot === 'background' ? ['image'] : ['model3d'],
+                    maxCount: 1,
+                    optional: true,
+                  }}
+                  onChoose={item => assignChoice(slot, capture, item)}
+                />
+              </div>
               {clips.length > 0 && (
                 <select
                   className="mt-1 w-full rounded border border-border bg-bg-tertiary px-1 py-0.5 disabled:opacity-40"
@@ -349,16 +395,6 @@ export function Scene3DWorkspace({ width, height }: Props) {
       {exportNote && <p className="text-[8px] text-cyan-100" data-testid="world3d-export-note">{exportNote}</p>}
       <p className="text-[8px] text-text-muted">{sceneDoc.templateId === 'run-loop' ? t('stage.runHelp') : t('stage.help')}</p>
       <span data-testid="scene3d-roundtrip" className="hidden">{roundtrip ? 'ok' : 'bad'}</span>
-      <AssetExplorerDialog
-        open={Boolean(explorerSlot)}
-        title={t('stage.fromApp')}
-        items={explorerItems}
-        onClose={() => setExplorerSlot(null)}
-        onChoose={item => {
-          if (item && explorerSlot) assignSource(explorerSlot, item.url, item.type === 'image' ? 'image' : 'model3d')
-          setExplorerSlot(null)
-        }}
-      />
     </div>
   )
 }
diff --git a/ui/src/features/scene3d/document.ts b/ui/src/features/scene3d/document.ts
index 4370bc5c..96fe530f 100644
--- a/ui/src/features/scene3d/document.ts
+++ b/ui/src/features/scene3d/document.ts
@@ -1,4 +1,5 @@
 import { parseScene3DLoop } from './backdrop.ts'
+import { durableScene3DSourceUrl, parseScene3DSourceRef } from './slotSource.ts'
 import { SCENE3D_TEMPLATE_IDS, type Scene3DDocument, type Scene3DSlot, type Scene3DTemplateId } from './types.ts'
 
 const SLOT_COLORS: Record<string, [number, number, number]> = {
@@ -71,11 +72,17 @@ export function parseScene3DDocument(raw: unknown): Scene3DDocument | null {
   const value = raw as Partial<Scene3DDocument>
   if (value.version !== 1 || value.units !== 'meters' || value.up !== 'y') return null
   if (!Array.isArray(value.slots) || !value.camera || !value.light) return null
-  const slots = value.slots.map(slot => ({
-    ...slot,
-    media: slot.media === 'image' ? 'image' as const : 'model3d' as const,
-    loop: parseScene3DLoop(slot.loop),
-  }))
+  const slots = value.slots.map(slot => {
+    const sourceUrl = durableScene3DSourceUrl(typeof slot.sourceUrl === 'string' ? slot.sourceUrl : '')
+    const sourceRef = parseScene3DSourceRef(slot.sourceRef)
+    return {
+      ...slot,
+      sourceUrl,
+      sourceRef: sourceUrl && sourceRef ? sourceRef : undefined,
+      media: slot.media === 'image' ? 'image' as const : 'model3d' as const,
+      loop: parseScene3DLoop(slot.loop),
+    }
+  })
   const templateId: Scene3DTemplateId = typeof value.templateId === 'string'
     && (SCENE3D_TEMPLATE_IDS as readonly string[]).includes(value.templateId)
     ? value.templateId as Scene3DTemplateId
diff --git a/ui/src/features/scene3d/slotSource.ts b/ui/src/features/scene3d/slotSource.ts
new file mode 100644
index 00000000..fe661bfa
--- /dev/null
+++ b/ui/src/features/scene3d/slotSource.ts
@@ -0,0 +1,94 @@
+import type { ApiOutput } from '../../api/outputs'
+import type { Scene3DSlotMedia, Scene3DSourceRef } from './types.ts'
+
+export type { Scene3DSourceRef }
+
+export type SlotSourceCapture = {
+  generation: number
+  slotId: string
+  templateId: string
+  workspaceId: string
+}
+
+export type SlotSourceLive = {
+  generation: number
+  slotId: string
+  templateId: string
+  workspaceId: string
+  exporting: boolean
+}
+
+export type SlotSourceCommit =
+  | { action: 'ignore' }
+  | { action: 'clear' }
+  | {
+    action: 'apply'
+    sourceUrl: string
+    sourceRef: Scene3DSourceRef
+    media: Scene3DSlotMedia
+    clip: null
+  }
+
+export function isTransientSourceUrl(url: string): boolean {
+  return url.startsWith('blob:') || url.startsWith('filesystem:')
+}
+
+export function parseScene3DSourceRef(raw: unknown): Scene3DSourceRef | undefined {
+  if (!raw || typeof raw !== 'object') return undefined
+  const value = raw as Partial<Scene3DSourceRef>
+  if (typeof value.workspaceId !== 'string' || !value.workspaceId) return undefined
+  if (typeof value.filename !== 'string' || !value.filename) return undefined
+  if (typeof value.url !== 'string' || !value.url || isTransientSourceUrl(value.url)) return undefined
+  const assetId = typeof value.assetId === 'string' && value.assetId ? value.assetId : undefined
+  return { workspaceId: value.workspaceId, filename: value.filename, url: value.url, assetId }
+}
+
+export function durableScene3DSourceUrl(url: string): string {
+  return typeof url === 'string' && url && !isTransientSourceUrl(url) ? url : ''
+}
+
+export function sourceRefFromOutput(item: ApiOutput, workspaceId: string): Scene3DSourceRef {
+  const extra = item as ApiOutput & { id?: string }
+  return {
+    workspaceId,
+    filename: item.name,
+    url: item.url,
+    assetId: typeof extra.id === 'string' && extra.id ? extra.id : undefined,
+  }
+}
+
+export function pickerOutputFromSlot(sourceUrl: string, media: Scene3DSlotMedia, sourceRef?: Scene3DSourceRef): ApiOutput | undefined {
+  const url = durableScene3DSourceUrl(sourceUrl)
+  if (!url) return undefined
+  return {
+    name: sourceRef?.filename || url.split('/').pop() || url,
+    type: media === 'image' ? 'image' : 'model3d',
+    mode: null,
+    size: 0,
+    created_at: 0,
+    url,
+    thumbnail_url: media === 'image' ? url : '',
+  }
+}
+
+export function commitSlotSourceChoice(
+  live: SlotSourceLive,
+  capture: SlotSourceCapture,
+  item: ApiOutput | null,
+): SlotSourceCommit {
+  if (live.exporting) return { action: 'ignore' }
+  if (live.generation !== capture.generation) return { action: 'ignore' }
+  if (live.slotId !== capture.slotId) return { action: 'ignore' }
+  if (live.templateId !== capture.templateId) return { action: 'ignore' }
+  if (live.workspaceId !== capture.workspaceId) return { action: 'ignore' }
+  if (!item) return { action: 'clear' }
+  if (isTransientSourceUrl(item.url) || !item.url || !item.name) return { action: 'ignore' }
+  const media: Scene3DSlotMedia = item.type === 'image' ? 'image' : 'model3d'
+  return {
+    action: 'apply',
+    sourceUrl: item.url,
+    sourceRef: sourceRefFromOutput(item, capture.workspaceId),
+    media,
+    clip: null,
+  }
+}
diff --git a/ui/src/features/scene3d/templates.ts b/ui/src/features/scene3d/templates.ts
index 9aada9db..4d24afe5 100644
--- a/ui/src/features/scene3d/templates.ts
+++ b/ui/src/features/scene3d/templates.ts
@@ -203,7 +203,7 @@ const DRESSING_BY_TEMPLATE: Partial<Record<Scene3DTemplateId, Scene3DDocument['d
 export function patchScene3DSlot(
   document: Scene3DDocument,
   slotId: string,
-  patch: Partial<Pick<Scene3DSlot, 'position' | 'rotationY' | 'scale' | 'sourceUrl' | 'media' | 'clip' | 'loop'>>,
+  patch: Partial<Pick<Scene3DSlot, 'position' | 'rotationY' | 'scale' | 'sourceUrl' | 'sourceRef' | 'media' | 'clip' | 'loop'>>,
 ): Scene3DDocument {
   return {
     ...document,
diff --git a/ui/src/features/scene3d/types.ts b/ui/src/features/scene3d/types.ts
index f8f2d6e7..3b1d057c 100644
--- a/ui/src/features/scene3d/types.ts
+++ b/ui/src/features/scene3d/types.ts
@@ -57,6 +57,13 @@ export type Scene3DLoop = {
 
 export type Scene3DDressing = 'none' | 'street' | 'space' | 'treadmill' | 'cafe' | 'drive-city' | 'drive-coast' | 'drive-tunnel'
 
+export type Scene3DSourceRef = {
+  workspaceId: string
+  filename: string
+  url: string
+  assetId?: string
+}
+
 export type Scene3DSlot = {
   id: string
   slot: Scene3DSlotId
@@ -64,6 +71,7 @@ export type Scene3DSlot = {
   rotationY: number
   scale: number
   sourceUrl: string
+  sourceRef?: Scene3DSourceRef
   media: Scene3DSlotMedia
   clip: Scene3DClipRef | null
   loop?: Scene3DLoop
diff --git a/ui/tests/scene3dSlotSource.test.mjs b/ui/tests/scene3dSlotSource.test.mjs
new file mode 100644
index 00000000..cccf53be
--- /dev/null
+++ b/ui/tests/scene3dSlotSource.test.mjs
@@ -0,0 +1,88 @@
+import assert from 'node:assert/strict'
+import test from 'node:test'
+import { applyScene3DTemplate } from '../src/features/scene3d/templates.ts'
+import { parseScene3DDocument } from '../src/features/scene3d/document.ts'
+import {
+  commitSlotSourceChoice,
+  durableScene3DSourceUrl,
+  pickerOutputFromSlot,
+} from '../src/features/scene3d/slotSource.ts'
+
+const live = {
+  generation: 3,
+  slotId: 'subject_1',
+  templateId: 'two-shot',
+  workspaceId: 'film',
+  exporting: false,
+}
+
+const capture = {
+  generation: 3,
+  slotId: 'subject_1',
+  templateId: 'two-shot',
+  workspaceId: 'film',
+}
+
+const catalog = {
+  name: 'hero.glb',
+  type: 'model3d',
+  mode: null,
+  size: 12,
+  created_at: 1,
+  url: '/api/v1/file/hero.glb?workspace=film',
+}
+
+test('catalog choice stores a durable url and workspace filename, not a blob', () => {
+  const result = commitSlotSourceChoice(live, capture, catalog)
+  assert.equal(result.action, 'apply')
+  if (result.action !== 'apply') return
+  assert.equal(result.sourceUrl.startsWith('blob:'), false)
+  assert.equal(result.sourceRef.filename, 'hero.glb')
+  assert.equal(result.sourceRef.workspaceId, 'film')
+  assert.equal(result.clip, null)
+})
+
+test('blob urls are not committed as a scene source', () => {
+  const result = commitSlotSourceChoice(live, capture, {
+    ...catalog,
+    url: 'blob:http://localhost/abc',
+  })
+  assert.equal(result.action, 'ignore')
+  assert.equal(durableScene3DSourceUrl('blob:http://localhost/abc'), '')
+})
+
+test('cancel clears; export, template, workspace or generation mismatch is ignored', () => {
+  assert.equal(commitSlotSourceChoice(live, capture, null).action, 'clear')
+  assert.equal(commitSlotSourceChoice({ ...live, exporting: true }, capture, catalog).action, 'ignore')
+  assert.equal(commitSlotSourceChoice({ ...live, generation: 9 }, capture, catalog).action, 'ignore')
+  assert.equal(commitSlotSourceChoice({ ...live, templateId: 'cafe-dance' }, capture, catalog).action, 'ignore')
+  assert.equal(commitSlotSourceChoice({ ...live, workspaceId: 'other' }, capture, catalog).action, 'ignore')
+  assert.equal(commitSlotSourceChoice({ ...live, slotId: 'subject_2' }, capture, catalog).action, 'ignore')
+})
+
+test('save and reopen keeps sourceRef and drops blob urls', () => {
+  const document = applyScene3DTemplate('two-shot')
+  document.slots[0].sourceUrl = '/api/v1/file/hero.glb?workspace=film'
+  document.slots[0].sourceRef = {
+    workspaceId: 'film',
+    filename: 'hero.glb',
+    url: '/api/v1/file/hero.glb?workspace=film',
+  }
+  document.slots[1].sourceUrl = 'blob:http://localhost/stale'
+  const restored = parseScene3DDocument(JSON.parse(JSON.stringify(document)))
+  assert.ok(restored)
+  assert.equal(restored.slots[0].sourceRef?.filename, 'hero.glb')
+  assert.equal(restored.slots[0].sourceUrl, '/api/v1/file/hero.glb?workspace=film')
+  assert.equal(restored.slots[1].sourceUrl, '')
+  assert.equal(restored.slots[1].sourceRef, undefined)
+  assert.equal(pickerOutputFromSlot(restored.slots[0].sourceUrl, 'model3d', restored.slots[0].sourceRef)?.name, 'hero.glb')
+})
+
+test('drive and cafe templates still expose only the documented slot roles', () => {
+  const cafe = applyScene3DTemplate('cafe-dance')
+  assert.deepEqual(cafe.slots.map(slot => slot.slot), ['subject_1'])
+  const chase = applyScene3DTemplate('drive-chase')
+  assert.deepEqual(chase.slots.map(slot => slot.slot), ['background'])
+  const hero = applyScene3DTemplate('drive-hero')
+  assert.deepEqual(hero.slots.map(slot => slot.slot), ['subject_1', 'background'])
+})