Code-execution outputs land on `messages.attachments` (set by
`processCodeOutput`), while user uploads land on `messages.files`.
The threadFileIds switch (#13004) walked only `files`, so on a
single linear thread:
Turn 1: assistant produces sample.xlsx → attachment with codeEnvRef
Turn 2: user says "add 2 rows"
→ primeCodeFiles: file_ids=0 resourceFiles=0
→ /exec sent files=[]
→ sandbox: FileNotFoundError: 'sample.xlsx'
The `getThreadData` walk found zero file_ids because the assistant's
codeEnvRef was on `attachments`, not `files`. Compounded by the
DB select string `'messageId parentMessageId files'` which didn't
pull `attachments` into memory in the first place — so even fixing
the walk in isolation wouldn't have surfaced them.
Both layers fixed:
- `ThreadMessage` type adds `attachments?: Array<{ file_id?: string }>`
- `getThreadData` walks both arrays, dedups via the same Set
- `initialize.ts` selects `'messageId parentMessageId files attachments'`
## Test plan
`packages/api/src/utils/message.spec.ts` (+6 cases):
- collects file_ids from `attachments`
- walks both `files` and `attachments` on the same message
- regression: linear thread with code-output attachments across
user→assistant→user→assistant produces the right file_ids
- dedupes shared ids that appear in both arrays
- skips attachments without file_id (mirrors `files` behavior)
- empty `attachments` array
`packages/api/src/agents/__tests__/initialize.test.ts` (+1 case):
- locks the DB select string includes `attachments` alongside
`files` / `messageId` / `parentMessageId`
- [x] `npx jest src/utils/message.spec.ts` — 39/39 pass
- [x] `npx jest src/agents/__tests__/initialize.test.ts` — 33/33 pass
- [x] lint clean on all four touched files
3d5e5348a4