fix(server): harden embedded web UI serving

Build on anomalyco#19299 by @thdxr with production hardening for the new
server architecture (anomalyco#19335):

- Add pre-bootstrap static middleware in server.ts before
  WorkspaceRouterMiddleware to avoid Instance.provide() + DB migration
  checks on every CSS/JS/image/font request
- Add SPA fallback routing — page routes (no extension) get index.html,
  asset requests (.js, .woff2) fall through to CDN proxy
- Add OPENCODE_APP_DIR env var for explicit dev override
- Auto-detect packages/app/dist in monorepo dev mode
- Use explicit MIME type map for consistent content-type headers
- CDN proxy fallback for assets not found locally/embedded

Author: BYK

packages/opencode/src/flag/flag.ts

@@ -73,6 +73,7 @@ export namespace Flag {
   export const OPENCODE_EXPERIMENTAL_MARKDOWN = !falsy("OPENCODE_EXPERIMENTAL_MARKDOWN")
   export const OPENCODE_MODELS_URL = process.env["OPENCODE_MODELS_URL"]
   export const OPENCODE_MODELS_PATH = process.env["OPENCODE_MODELS_PATH"]
+  export const OPENCODE_APP_DIR = process.env["OPENCODE_APP_DIR"]
   export const OPENCODE_DISABLE_EMBEDDED_WEB_UI = truthy("OPENCODE_DISABLE_EMBEDDED_WEB_UI")
   export const OPENCODE_DB = process.env["OPENCODE_DB"]
   export const OPENCODE_DISABLE_CHANNEL_DB = truthy("OPENCODE_DISABLE_CHANNEL_DB")

packages/opencode/src/server/instance.ts

@@ -29,17 +29,85 @@ import { errorHandler } from "./middleware"
 
 const log = Log.create({ service: "server" })
 
-const embeddedUIPromise = Flag.OPENCODE_DISABLE_EMBEDDED_WEB_UI
+export const embeddedUIPromise = Flag.OPENCODE_DISABLE_EMBEDDED_WEB_UI
   ? Promise.resolve(null)
   : // @ts-expect-error - generated file at build time
     import("opencode-web-ui.gen.ts").then((module) => module.default as Record<string, string>).catch(() => null)
 
-const DEFAULT_CSP =
+const CSP =
   "default-src 'self'; script-src 'self' 'wasm-unsafe-eval'; style-src 'self' 'unsafe-inline'; img-src 'self' data: https:; font-src 'self' data:; media-src 'self' data:; connect-src 'self' data:"
 
 const csp = (hash = "") =>
   `default-src 'self'; script-src 'self' 'wasm-unsafe-eval'${hash ? ` 'sha256-${hash}'` : ""}; style-src 'self' 'unsafe-inline'; img-src 'self' data: https:; font-src 'self' data:; media-src 'self' data:; connect-src 'self' data:`
 
+const MIME: Record<string, string> = {
+  html: "text/html; charset=utf-8",
+  js: "application/javascript",
+  mjs: "application/javascript",
+  css: "text/css",
+  json: "application/json",
+  png: "image/png",
+  jpg: "image/jpeg",
+  jpeg: "image/jpeg",
+  gif: "image/gif",
+  svg: "image/svg+xml",
+  ico: "image/x-icon",
+  woff: "font/woff",
+  woff2: "font/woff2",
+  ttf: "font/ttf",
+  wasm: "application/wasm",
+  txt: "text/plain",
+  webmanifest: "application/manifest+json",
+}
+
+function mime(path: string) {
+  return MIME[path.split(".").pop() ?? ""] ?? "application/octet-stream"
+}
+
+// Resolve local app directory for dev. Resolution order:
+//   1. OPENCODE_APP_DIR env var (explicit override)
+//   2. Auto-detect packages/app/dist relative to this file (monorepo dev)
+// Embedded assets are handled separately via embeddedUIPromise.
+let _appDir: string | false | undefined
+export function resolveAppDir(): string | undefined {
+  if (_appDir !== undefined) return _appDir || undefined
+  if (Flag.OPENCODE_APP_DIR) {
+    _appDir = Flag.OPENCODE_APP_DIR
+    return _appDir
+  }
+  try {
+    const url = new URL("../../../app/dist", import.meta.url)
+    if (url.protocol === "file:" && Bun.file(url.pathname + "/index.html").size > 0) {
+      _appDir = url.pathname
+      return _appDir
+    }
+  } catch {}
+  _appDir = false
+  return undefined
+}
+
+export function serveEmbedded(reqPath: string, manifest: Record<string, string>): Response | undefined {
+  const key = reqPath === "/" ? "index.html" : reqPath.replace(/^\//, "")
+  const bunfs = manifest[key]
+  if (!bunfs) return undefined
+  const file = Bun.file(bunfs)
+  if (file.size > 0)
+    return new Response(file, {
+      headers: { "Content-Type": mime(key), "Content-Security-Policy": CSP },
+    })
+  return undefined
+}
+
+export function serveFile(reqPath: string, dir: string): Response | undefined {
+  const rel = reqPath === "/" ? "/index.html" : reqPath
+  const file = Bun.file(dir + rel)
+  if (file.size > 0)
+    return new Response(file, {
+      headers: { "Content-Type": mime(rel), "Content-Security-Policy": CSP },
+    })
+  return undefined
+}
+
 export const InstanceRoutes = (app?: Hono) =>
   (app ?? new Hono())
     .onError(errorHandler(log))
@@ -249,37 +317,49 @@ export const InstanceRoutes = (app?: Hono) =>
       },
     )
     .all("/*", async (c) => {
-      const embeddedWebUI = await embeddedUIPromise
-      const path = c.req.path
+      const embedded = await embeddedUIPromise
+      const reqPath = c.req.path
+
+      // Try embedded asset
+      if (embedded) {
+        const res = serveEmbedded(reqPath, embedded)
+        if (res) return res
+      }
+
+      // Try local app dir
+      const dir = resolveAppDir()
+      if (dir) {
+        const res = serveFile(reqPath, dir)
+        if (res) return res
+      }
 
-      if (embeddedWebUI) {
-        const match = embeddedWebUI[path.replace(/^\//, "")] ?? embeddedWebUI["index.html"] ?? null
-        if (!match) return c.json({ error: "Not Found" }, 404)
-        const file = Bun.file(match)
-        if (await file.exists()) {
-          c.header("Content-Type", file.type)
-          if (file.type.startsWith("text/html")) {
-            c.header("Content-Security-Policy", DEFAULT_CSP)
-          }
-          return c.body(await file.arrayBuffer())
-        } else {
-          return c.json({ error: "Not Found" }, 404)
+      // SPA fallback: return index.html for page routes (no file extension).
+      // Asset requests (.js, .css, .woff2) skip this and fall through to CDN.
+      if (!/\.[a-zA-Z0-9]+$/.test(reqPath)) {
+        if (embedded) {
+          const idx = serveEmbedded("/index.html", embedded)
+          if (idx) return idx
+        }
+        if (dir) {
+          const idx = serveFile("/index.html", dir)
+          if (idx) return idx
         }
-      } else {
-        const response = await proxy(`https://app.opencode.ai${path}`, {
-          ...c.req,
-          headers: {
-            ...c.req.raw.headers,
-            host: "app.opencode.ai",
-          },
-        })
-        const match = response.headers.get("content-type")?.includes("text/html")
-          ? (await response.clone().text()).match(
-              /<script\b(?![^>]*\bsrc\s*=)[^>]*\bid=(['"])oc-theme-preload-script\1[^>]*>([\s\S]*?)<\/script>/i,
-            )
-          : undefined
-        const hash = match ? createHash("sha256").update(match[2]).digest("base64") : ""
-        response.headers.set("Content-Security-Policy", csp(hash))
-        return response
       }
+
+      // CDN proxy fallback for missing assets
+      const response = await proxy(`https://app.opencode.ai${reqPath}`, {
+        ...c.req,
+        headers: {
+          ...c.req.raw.headers,
+          host: "app.opencode.ai",
+        },
+      })
+      const match = response.headers.get("content-type")?.includes("text/html")
+        ? (await response.clone().text()).match(
+            /<script\b(?![^>]*\bsrc\s*=)[^>]*\bid=(['"])oc-theme-preload-script\1[^>]*>([\s\S]*?)<\/script>/i,
+          )
+        : undefined
+      const hash = match ? createHash("sha256").update(match[2]).digest("base64") : ""
+      response.headers.set("Content-Security-Policy", csp(hash))
+      return response
     })

packages/opencode/src/server/server.ts

@@ -15,7 +15,7 @@ import { GlobalRoutes } from "./routes/global"
 import { MDNS } from "./mdns"
 import { lazy } from "@/util/lazy"
 import { errorHandler } from "./middleware"
-import { InstanceRoutes } from "./instance"
+import { InstanceRoutes, embeddedUIPromise, resolveAppDir, serveEmbedded, serveFile } from "./instance"
 import { initProjectors } from "./projectors"
 
 // @ts-ignore This global is needed to prevent ai-sdk from logging warnings to stdout https://github.com/vercel/ai/blob/2dc67e0ef538307f21368db32d5a12345d98831b/packages/ai/src/logger/log-warnings.ts#L85
@@ -234,6 +234,21 @@ export namespace Server {
           return c.json(true)
         },
       )
+      .use(async (c, next) => {
+        // Serve static assets before WorkspaceRouterMiddleware to avoid
+        // Instance.provide() + InstanceBootstrap on every asset request.
+        const embedded = await embeddedUIPromise
+        if (embedded) {
+          const res = serveEmbedded(c.req.path, embedded)
+          if (res) return res
+        }
+        const dir = resolveAppDir()
+        if (dir) {
+          const res = serveFile(c.req.path, dir)
+          if (res) return res
+        }
+        return next()
+      })
       .use(WorkspaceRouterMiddleware)
   }