fix: resolve local-process wait after child close

.changeset/fix-local-process-wait.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/ai-sandbox-local-process': patch
+---
+
+Fix local-process spawn handles hanging when the child exits before `wait()` is called.

packages/ai-sandbox-local-process/src/handle.ts

@@ -340,6 +340,13 @@ export class LocalProcessHandle implements SandboxHandle {
         once: true,
       })
     }
+    const closed = new Promise<number>((resolve, reject) => {
+      child.once('error', reject)
+      child.once('close', (code) => resolve(code ?? 0))
+    })
+    // The child can close while stdout is still being drained. Keep the
+    // rejection handled until the caller asks for the result via wait().
+    closed.catch(() => {})
     const handle: SpawnHandle = {
       pid: child.pid ?? -1,
       stdout: decodeStream(child.stdout),
@@ -354,11 +361,7 @@ export class LocalProcessHandle implements SandboxHandle {
             child.stdin.end(() => resolve())
           }),
       },
-      wait: () =>
-        new Promise<number>((resolve, reject) => {
-          child.on('error', reject)
-          child.on('close', (code) => resolve(code ?? 0))
-        }),
+      wait: () => closed,
       kill: (signal) => {
         killTree(child, signal)
         return Promise.resolve()

packages/ai-sandbox-local-process/tests/local-process.test.ts

@@ -88,6 +88,24 @@ describe('local-process process', () => {
     expect(code).toBe(0)
     await sbx.destroy()
   })
+
+  it('resolves wait() when the child closes before stdout is fully consumed', async () => {
+    const sbx = await fresh()
+    const proc = await sbx.process.spawn(
+      `node -e "for (let i = 0; i < 20; i++) console.log(i)"`,
+    )
+    let out = ''
+    for await (const chunk of proc.stdout) {
+      out += chunk
+      await new Promise((resolve) => setTimeout(resolve, 10))
+    }
+    await expect(proc.wait()).resolves.toBe(0)
+    const lines = out.trimEnd().split(/\r?\n/)
+    expect(lines).toEqual(
+      Array.from({ length: 20 }, (_, index) => String(index)),
+    )
+    await sbx.destroy()
+  })
 })
 
 describe('local-process + spawnNdjson (real agent-CLI streaming)', () => {