## Why
`thread/attachment/list` lists attachments for a known thread. Clients also need to find the threads associated with a given attachment identity.
## What changed
Add `thread/attachmentOwner/list` to return owning thread IDs and archive status for an exact `attachmentType` and `identityKey`. Support cursor pagination and an optional `archived` filter, including both archived and non-archived threads by default.
Wire the request through the thread store and update documentation, protocol schemas, and generated TypeScript and Python types. The lookup is limited to the configured thread store and reports current membership, not an atomic resource-cleanup check.
## Testing
Extend app-server integration tests to cover exact type-and-key matching, multiple owners, archive filtering, and invalid cursor rejection.
GitOrigin-RevId: 30f4a20e00243d0023246d465a9b95213b3adeb6
## What changed
- Add `thread/attachment/add`, `thread/attachment/list`, and `thread/attachment/remove` to manage durable resource references without loading the owning thread or changing conversation history.
- Identify attachments by thread, `attachmentType`, and `identityKey`. Repeated adds return the existing attachment; repeated removals succeed without emitting another update. Listing supports cursor pagination.
- Broadcast `thread/attachment/updated` after creation or deletion, after responding to the requester. Serialize attachment mutations with thread lifecycle operations and reject stores that do not support attachments.
- Update protocol schemas, TypeScript and Python bindings, documentation, and TUI notification handling so attachment updates do not add untracked threads to the agent picker.
## Testing
Add coverage for unloaded threads, pagination, idempotent addition and removal, reattachment, invalid inputs, unsupported stores, response-before-notification ordering across clients, and TUI notification routing.
GitOrigin-RevId: 0d29cf903afd4e931a70a9cf96300475213b34aa
joeytrasatti-openai