fix(worker): make user-box lifecycle concurrency-safe

apps/agent-worker/src/terminal.ts

@@ -4,9 +4,10 @@ import type { Server } from 'node:http';
 import type { WebSocket } from 'ws';
 import { WebSocketServer } from 'ws';
 
+import type { BoxHandle } from './user-container';
 import { env } from './env';
 import { verifyTerminalToken } from './terminal-token';
-import { acquireUserBox, releaseUserBox } from './user-container';
+import { acquireUserBox } from './user-container';
 import { getTerminalWorkspace } from './worker';
 
 const clampDimension = (value: unknown) => {
@@ -63,7 +64,7 @@ const bridge = async (ws: WebSocket, jobId: string) => {
     else pendingInput.push(data);
   });
 
-  let acquired = false;
+  const handleHolder: { current?: BoxHandle } = {};
   let released = false;
   // Read through a function so TS doesn't narrow `released` to a constant — the
   // cleanup handler flips it asynchronously when the socket closes.
@@ -72,7 +73,7 @@ const bridge = async (ws: WebSocket, jobId: string) => {
     if (released) return;
     released = true;
     procHolder.current?.kill();
-    if (acquired) releaseUserBox(workspace.username);
+    handleHolder.current?.release();
   };
   ws.on('close', cleanup);
   ws.on('error', cleanup);
@@ -81,12 +82,13 @@ const bridge = async (ws: WebSocket, jobId: string) => {
   // the terminal share the exact same container (Phase 2).
   let boxName: string;
   try {
-    boxName = await acquireUserBox({
+    const handle = await acquireUserBox({
       username: workspace.username,
       workdir: workspace.workdir,
       containerHome: workspace.containerHome,
     });
-    acquired = true;
+    handleHolder.current = handle;
+    boxName = handle.boxName;
   } catch (error) {
     ws.close(
       1011,
@@ -95,7 +97,11 @@ const bridge = async (ws: WebSocket, jobId: string) => {
     return;
   }
 
-  if (isReleased()) return; // client disconnected during startup; cleanup ran
+  // Cleanup may have run before the awaited handle existed.
+  if (isReleased()) {
+    handleHolder.current.release();
+    return;
+  }
 
   // Reattach a persistent tmux session across reconnects when available, else a
   // plain login shell. `stty` sizes the PTY to the client's viewport up front.