fix(app): terminal replay (#12991)

packages/opencode/src/pty/index.ts

@@ -15,6 +15,17 @@ export namespace Pty {
 
   const BUFFER_LIMIT = 1024 * 1024 * 2
   const BUFFER_CHUNK = 64 * 1024
+  const encoder = new TextEncoder()
+
+  // WebSocket control frame: 0x00 + UTF-8 JSON (currently { cursor }).
+  const meta = (cursor: number) => {
+    const json = JSON.stringify({ cursor })
+    const bytes = encoder.encode(json)
+    const out = new Uint8Array(bytes.length + 1)
+    out[0] = 0
+    out.set(bytes, 1)
+    return out
+  }
 
   const pty = lazy(async () => {
     const { spawn } = await import("bun-pty")
@@ -68,6 +79,8 @@ export namespace Pty {
     info: Info
     process: IPty
     buffer: string
+    bufferCursor: number
+    cursor: number
     subscribers: Set<WSContext>
   }
 
@@ -139,23 +152,27 @@ export namespace Pty {
       info,
       process: ptyProcess,
       buffer: "",
+      bufferCursor: 0,
+      cursor: 0,
       subscribers: new Set(),
     }
     state().set(id, session)
     ptyProcess.onData((data) => {
-      let open = false
+      session.cursor += data.length
+
       for (const ws of session.subscribers) {
         if (ws.readyState !== 1) {
           session.subscribers.delete(ws)
           continue
         }
-        open = true
         ws.send(data)
       }
-      if (open) return
+
       session.buffer += data
       if (session.buffer.length <= BUFFER_LIMIT) return
-      session.buffer = session.buffer.slice(-BUFFER_LIMIT)
+      const excess = session.buffer.length - BUFFER_LIMIT
+      session.buffer = session.buffer.slice(excess)
+      session.bufferCursor += excess
     })
     ptyProcess.onExit(({ exitCode }) => {
       log.info("session exited", { id, exitCode })
@@ -215,28 +232,47 @@ export namespace Pty {
     }
   }
 
-  export function connect(id: string, ws: WSContext) {
+  export function connect(id: string, ws: WSContext, cursor?: number) {
     const session = state().get(id)
     if (!session) {
       ws.close()
       return
     }
     log.info("client connected to session", { id })
-    session.subscribers.add(ws)
-    if (session.buffer) {
-      const buffer = session.buffer.length <= BUFFER_LIMIT ? session.buffer : session.buffer.slice(-BUFFER_LIMIT)
-      session.buffer = ""
+
+    const start = session.bufferCursor
+    const end = session.cursor
+
+    const from =
+      cursor === -1 ? end : typeof cursor === "number" && Number.isSafeInteger(cursor) ? Math.max(0, cursor) : 0
+
+    const data = (() => {
+      if (!session.buffer) return ""
+      if (from >= end) return ""
+      const offset = Math.max(0, from - start)
+      if (offset >= session.buffer.length) return ""
+      return session.buffer.slice(offset)
+    })()
+
+    if (data) {
       try {
-        for (let i = 0; i < buffer.length; i += BUFFER_CHUNK) {
-          ws.send(buffer.slice(i, i + BUFFER_CHUNK))
+        for (let i = 0; i < data.length; i += BUFFER_CHUNK) {
+          ws.send(data.slice(i, i + BUFFER_CHUNK))
         }
       } catch {
-        session.subscribers.delete(ws)
-        session.buffer = buffer
         ws.close()
         return
       }
     }
+
+    try {
+      ws.send(meta(end))
+    } catch {
+      ws.close()
+      return
+    }
+
+    session.subscribers.add(ws)
     return {
       onMessage: (message: string | ArrayBuffer) => {
         session.process.write(String(message))

packages/opencode/src/server/routes/pty.ts

@@ -151,11 +151,18 @@ export const PtyRoutes = lazy(() =>
       validator("param", z.object({ ptyID: z.string() })),
       upgradeWebSocket((c) => {
         const id = c.req.param("ptyID")
+        const cursor = (() => {
+          const value = c.req.query("cursor")
+          if (!value) return
+          const parsed = Number(value)
+          if (!Number.isSafeInteger(parsed) || parsed < -1) return
+          return parsed
+        })()
         let handler: ReturnType<typeof Pty.connect>
         if (!Pty.get(id)) throw new Error("Session not found")
         return {
           onOpen(_event, ws) {
-            handler = Pty.connect(id, ws)
+            handler = Pty.connect(id, ws, cursor)
           },
           onMessage(event) {
             handler?.onMessage(String(event.data))