fix: rewrite {version}/assets/ requests to the sidecar's per-entity JIT lane

The flat /assets/{file} lane only serves bundles already in the sidecar's
index: anything rebuilt or not yet built after a scene edit 404s, since only
the legacy {version}/{entity}/{file} lane resolves digests tolerantly and
JIT-builds on miss. Rewrite there instead, deriving the entity id the same
way the preview content server does and dropping the deps digest from the
file name (bare b64 hashes never contain '_').

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: dalkia

packages/@dcl/sdk-commands/src/commands/start/server/asset-bundles-proxy.ts

@@ -2,6 +2,8 @@ import { Router } from '@well-known-components/http-server'
 import { Readable } from 'stream'
 
 import { CliComponents } from '../../../components'
+import { Workspace } from '../../../logic/workspace-validations'
+import { b64UrlHashingFunction } from '../../../logic/project-files'
 import { PreviewComponents } from '../types'
 
 /**
@@ -18,8 +20,13 @@ import { PreviewComponents } from '../types'
 export function setupAssetBundlesProxy(
   components: Pick<CliComponents, 'fetch'>,
   router: Router<PreviewComponents>,
-  getSidecarUrl: () => string | undefined
+  getSidecarUrl: () => string | undefined,
+  workspace: Workspace
 ) {
+  // Same derivation the preview content server uses for the scene's entity id
+  // (endpoints.ts getSceneJson). Multi-project workspaces keep the first project's
+  // id: local scene development previews a single scene.
+  const sceneId = b64UrlHashingFunction(workspace.projects[0].workingDirectory)
   router.all('/optimized-assets/:path+', async (ctx) => {
     const sidecarUrl = getSidecarUrl()
     if (!sidecarUrl) {
@@ -43,11 +50,15 @@ export function setupAssetBundlesProxy(
     const rawPath = Array.isArray(ctx.params.path) ? ctx.params.path.join('/') : ctx.params.path
 
     // Explorer requests v49+ scene bundles by their digest-bearing file name under the
-    // CDN's shared {version}/assets/ prefix (unity-explorer#9442). The sidecar serves
-    // those same files through its flat /assets/{file} lane (bundle-index lookup) but
-    // has no version-prefixed route, so strip the version segment on the way through.
+    // CDN's shared {version}/assets/ prefix (unity-explorer#9442). The sidecar has no
+    // such route — its digest-tolerant, JIT-building lane is the legacy per-entity one —
+    // so rewrite to {version}/{sceneId}/{hash}_{platform}, dropping the deps digest
+    // (bare b64 hashes never contain '_', so the digest segment is unambiguous).
     // TODO: drop once abgen serves GET /{version}/assets/{file} natively.
-    const path = rawPath.replace(/^v\d+\/assets\//, 'assets/')
+    const path = rawPath.replace(
+      /^(v\d+)\/assets\/(.+?)(?:_[0-9a-f]{32})?(_(?:windows|mac|linux)(?:\.br)?)$/,
+      (_match, version, hash, platform) => `${version}/${sceneId}/${hash}${platform}`
+    )
 
     const response = await components.fetch.fetch(`${sidecarUrl}/${path}${ctx.url.search}`, {
       headers: requestHeaders,

packages/@dcl/sdk-commands/src/commands/start/server/routes.ts

@@ -21,7 +21,7 @@ export async function wireRouter(
   const router = new Router<PreviewComponents>()
 
   if (getAssetBundlesSidecarUrl) {
-    setupAssetBundlesProxy(components, router, getAssetBundlesSidecarUrl)
+    setupAssetBundlesProxy(components, router, getAssetBundlesSidecarUrl, workspace)
   }
 
   if (dataLayer) {

test/sdk-commands/commands/start/asset-bundles-proxy.spec.ts

@@ -1,10 +1,14 @@
 import { setupAssetBundlesProxy } from '../../../../packages/@dcl/sdk-commands/src/commands/start/server/asset-bundles-proxy'
+import { b64UrlHashingFunction } from '../../../../packages/@dcl/sdk-commands/src/logic/project-files'
+
+const workspace = { projects: [{ workingDirectory: '/tmp/scene' }] } as any
+const sceneId = b64UrlHashingFunction('/tmp/scene')
 
 function makeProxy(getSidecarUrl: () => string | undefined) {
   const fetch = jest.fn()
   let handler: (ctx: any) => Promise<any>
   const router = { all: jest.fn((_path: string, h: any) => (handler = h)) }
-  setupAssetBundlesProxy({ fetch: { fetch } } as any, router as any, getSidecarUrl)
+  setupAssetBundlesProxy({ fetch: { fetch } } as any, router as any, getSidecarUrl, workspace)
   // requests reach the handler with the /optimized-assets prefix already
   // consumed by the route pattern: ctx.params.path carries the rest
   const dispatch = (method: string, path: string, search = '', body?: any, headers: Record<string, string> = {}) =>
@@ -68,16 +72,22 @@ describe('start/server/asset-bundles-proxy', () => {
     await expect(readBody(response.body)).resolves.toBe('bundle-bytes')
   })
 
-  it('rewrites the version-prefixed assets/ shape to the flat assets/ lane the sidecar serves', async () => {
+  it('rewrites digest-bearing {version}/assets/ requests to the legacy per-entity lane, dropping the digest', async () => {
     const { fetch, dispatch } = makeProxy(() => 'http://127.0.0.1:53211')
     fetch.mockResolvedValue(new Response('bundle-bytes', { status: 200 }))
 
     await dispatch('GET', 'v49/assets/b64-abc_7580fefaf1c77b8b771687a8a4f86063_mac')
 
-    expect(fetch).toHaveBeenCalledWith(
-      'http://127.0.0.1:53211/assets/b64-abc_7580fefaf1c77b8b771687a8a4f86063_mac',
-      expect.anything()
-    )
+    expect(fetch).toHaveBeenCalledWith(`http://127.0.0.1:53211/v49/${sceneId}/b64-abc_mac`, expect.anything())
+  })
+
+  it('rewrites digest-less {version}/assets/ requests to the legacy per-entity lane', async () => {
+    const { fetch, dispatch } = makeProxy(() => 'http://127.0.0.1:53211')
+    fetch.mockResolvedValue(new Response('bundle-bytes', { status: 200 }))
+
+    await dispatch('GET', 'v49/assets/b64-abc_windows.br')
+
+    expect(fetch).toHaveBeenCalledWith(`http://127.0.0.1:53211/v49/${sceneId}/b64-abc_windows.br`, expect.anything())
   })
 
   it('forwards non-GET methods with their body and the sidecar status', async () => {