## Why
A message's model-visible item ID may be unknown until the recipient records it. Message lifecycle observers need to capture publication state before that point.
## What changed
Remove `message_id` from `MessageLifecycleInput` and give each publication's `ExtensionData` a fresh UUID key. Stop assigning an item ID when publishing messages for lifecycle observers.
## Testing
Update the agent mailbox test to store a contributor-specific token in `ExtensionData` at publication and retrieve it at consumption, verifying that publication state survives queued delivery and recipient eviction.
GitOrigin-RevId: e254f94994d0976e61cb46ee23297f3248b9a389
## What changed
- Add `CodexThread::create_child` to create an idle child from a live tool invocation using a host-reserved thread ID and controller.
- Add `prepare_child` and `ThreadManager::create_prepared_child` to capture inherited settings and fresh or forked history, then start the child on another manager even after the parent shuts down. Reject detached preparation when live bindings cannot be transferred.
- Add opt-in `HostToolInvocationLookup` to track live calls and reject duplicate active call IDs within a turn. Revoke invocation access when dispatch ends and clean up provisional children when startup fails or is cancelled.
## Testing
Add tests for invocation lifetime and call ID reservation, inherited policy and live bindings, detached startup with fresh and full history, and cancellation cleanup.
GitOrigin-RevId: 71f17ecb4cd7636517e675df59289a8e8c7105b8
## What changed
Add `MessageLifecycleContributor` hooks to capture extension state when local agent control publishes a message and notify contributors when the recipient commits it to history, before sampling.
Carry shared delivery state through submissions, input queues, and mailbox eviction with `PendingAgentMessage`. Notify consumption at most once per delivery, release captured state when consumed or abandoned, and drop pending mail outside queue locks. Preserve the serialized message format without republishing restored history.
## Testing
Extend the mailbox eviction test to verify that publication state survives eviction and retained messages are consumed before the first resumed model sample.
GitOrigin-RevId: 9a1f6832bd48ec646a3fd179485c095e8dcc72cc
Ruslan Nigmatullin