test(integration): wait for the CLI child to exit before the lazy-recovery test resolves

[cpacker]

Summary

API / windows-latest / 4 has been failing on main with the same error on four pushes since 2026-09-13 20:53 UTC (889987b, 690c6dd, 232d320, b100c2d) and twice on #4431:

(pass) lazy approval recovery > handles concurrent message while approval is pending
error: EBUSY: resource busy or locked, rm C:\Users\RUNNER~1\AppData\Local\Temp\letta-code-test-home-xxxxxx
      at cleanup (scripts/test-home-preload.ts:70:5)
(fail) (unnamed)

The test itself passes. runLazyRecoveryTest resolved its promise the moment the final result frame arrived and scheduled proc.kill() 500 ms later. The test-home preload's afterAll runs rmSync(testHome) as soon as the test resolves, so it races the still-running CLI child, which holds files under that HOME. Windows refuses to remove a directory with open handles; Linux and macOS let it go.

Fix: record the outcome when the result frame arrives, but resolve the promise from the child's close handler, which fires after the child's stdio has closed. The 500 ms grace-then-kill stays. The fallback for a child that exits on its own (resolve from whatever it produced) is unchanged.

Verification

• bun run typecheck and biome on the file.
• The test cannot run in this sandbox (the CLI's --new-agent startup returns 404 Agent not found under the sandbox key on main as well), so the live check is this PR's API workflow, which runs this file on Linux, macOS, and Windows. I will report the Windows shard result.

Breadcrumbs

• Letta conversation: conv-bbe7b4f3-52f5-4aa0-9fe5-6eac06747473
• Origin: red API / windows-latest / 4 on fix(listener): only the execution owner resumes an interrupted turn on sync [LET-12476] #4431 traced to the same failure on main runs 34782170459, 34788537408, 34789048188, 34791820153.
• Related: scripts/test-home-preload.ts cleanup added in fix(test): isolate user home state #3703; unchanged here.

AI Disclosure

• This pull request was written entirely by a human
• This pull request was written with AI assistance and reviewed and edited by a human
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AI Tool(s) Used

Letta Code

Human Verification

I have reviewed and understand every change in this pull request and take responsibility for its correctness.

[letta-integration]

This exact child-exit cleanup change is now on main through #4453 (merge 6304454), also included in #4452. Verified the file on current main matches this PR’s fix. Closing this redundant PR; no additional merge is needed.