fix(app): parse session messages off thread

packages/app/src/context/server-session.ts

@@ -189,7 +189,11 @@ function reconcileFetched<T extends { id: string }>(
   return [...result.values()].sort((a, b) => cmp(a.id, b.id))
 }
 
-type ServerSessionOptions = { retry?: typeof retry; protocol?: Promise<"v1" | "v2"> }
+type ServerSessionOptions = {
+  retry?: typeof retry
+  protocol?: Promise<"v1" | "v2">
+  decodeMessages?: <T>(buffer: ArrayBuffer) => Promise<T>
+}
 
 export function createServerSession(
   client: OpencodeClient,
@@ -573,9 +577,17 @@ export function createServerSession(
         complete: response.data.length === 0,
       }
     }
-    const response = await (options?.retry ?? retry)(() => {
+    const response = await (options?.retry ?? retry)(async () => {
       onAttempt?.()
-      return client.session.messages({ sessionID, limit, before })
+      if (!options?.decodeMessages) return client.session.messages({ sessionID, limit, before })
+      const response = await client.session.messages({ sessionID, limit, before }, { parseAs: "arrayBuffer" })
+      if (!(response.data instanceof ArrayBuffer)) throw new Error("Session messages response is not an ArrayBuffer")
+      return {
+        ...response,
+        data: await options.decodeMessages<NonNullable<Awaited<ReturnType<typeof client.session.messages>>["data"]>>(
+          response.data,
+        ),
+      }
     })
     await yieldToMain()
     const items = (response.data ?? []).filter((item) => !!item?.info?.id)

packages/app/src/context/server-sync.tsx

@@ -59,6 +59,7 @@ import type {
 } from "@opencode-ai/client/promise"
 import { toggleMcp } from "./global-sync/mcp"
 import { createServerSession, type ServerSession } from "./server-session"
+import { decodeSessionMessages } from "./session-message-decoder"
 
 type GlobalStore = {
   ready: boolean
@@ -226,6 +227,7 @@ export function createServerSyncContextInner(serverSDK: ServerSDK) {
 
   const session = createServerSession(serverSDK.client, serverSDK.api.session, serverSDK.api.message, {
     protocol: serverSDK.protocol,
+    decodeMessages: decodeSessionMessages,
   })
   const queryOptionsApi = makeQueryOptionsApi(
     serverSDK.scope,

packages/app/src/context/session-message-decoder.ts

@@ -0,0 +1,38 @@
+import SessionMessageDecoderWorkerUrl from "./session-message-decoder.worker.ts?worker&url"
+
+type Response = { id: number; data?: unknown; error?: string }
+
+let worker: Worker | undefined
+let nextID = 0
+const pending = new Map<number, { resolve: (value: unknown) => void; reject: (error: Error) => void }>()
+
+export function decodeSessionMessages<T>(buffer: ArrayBuffer) {
+  const id = ++nextID
+  return new Promise<T>((resolve, reject) => {
+    pending.set(id, { resolve: (value) => resolve(value as T), reject })
+    getWorker().postMessage({ id, buffer }, [buffer])
+  })
+}
+
+function getWorker() {
+  if (worker) return worker
+  worker = new Worker(SessionMessageDecoderWorkerUrl, { type: "module" })
+  worker.onmessage = (event: MessageEvent<Response>) => {
+    const request = pending.get(event.data.id)
+    if (!request) return
+    pending.delete(event.data.id)
+    if (event.data.error) {
+      request.reject(new Error(event.data.error))
+      return
+    }
+    request.resolve(event.data.data)
+  }
+  worker.onerror = (event) => {
+    const error = new Error(event.message)
+    pending.forEach((request) => request.reject(error))
+    pending.clear()
+    worker?.terminate()
+    worker = undefined
+  }
+  return worker
+}

packages/app/src/context/session-message-decoder.worker.ts

@@ -0,0 +1,12 @@
+type DecoderRequest = { id: number; buffer: ArrayBuffer }
+
+self.onmessage = (event: MessageEvent<DecoderRequest>) => {
+  try {
+    const text = new TextDecoder().decode(event.data.buffer)
+    self.postMessage({ id: event.data.id, data: text ? JSON.parse(text) : {} })
+  } catch (error) {
+    self.postMessage({ id: event.data.id, error: error instanceof Error ? error.message : String(error) })
+  }
+}
+
+export {}