## Why
The `ItemIds` path fills in missing IDs before response items are
persisted and emitted as raw item events. `ResponseItem::AgentMessage`
is part of that same response-item stream, but it was skipped by the
missing-ID repair path, leaving agent messages without stable item IDs
while messages and tool items received generated IDs.
Agent messages recorded through `InterAgentCommunication` also need the
generated ID to survive rollout persistence and resume. Otherwise
clients can observe an `amsg_` ID for the live raw response item, then
see that same persisted agent message lose its item ID after restart.
## What changed
- Assign missing `ResponseItem::AgentMessage` IDs with the `amsg_`
prefix.
- Persist the generated item ID on `InterAgentCommunication` and replay
it back into the reconstructed `ResponseItem::AgentMessage` on resume.
- Keep the persisted ID out of the model-visible inter-agent message
envelope.
- Keep `CompactionTrigger` and `Other` skipped because they do not get
generated item IDs.
- Update session/protocol tests for agent-message ID assignment and
resume preservation.
## Manual Testing
Run the local dev build using `just c --enable item_ids` to ensure this
code is exercised:
https://github.com/openai/codex/blob/322e33512b2d38d38d705e2ef692a8aca50decac/codex-rs/core/src/session/mod.rs#L2713-L2715
In the `.jsonl` file, I saw entries like:
```json
{
"timestamp": "2026-06-24T00:44:03.098Z",
"type": "inter_agent_communication",
"payload": {
"id": "amsg_019ef715-849a-7a50-becc-ce63c6a9c994",
```
## Test plan
- `just test -p codex-core
record_inter_agent_communication_preserves_item_id_in_rollout_and_resume`
- `just test -p codex-core
record_inter_agent_communication_sets_turn_id_in_rollout_and_resume`
- `just test -p codex-protocol
inter_agent_communication_response_input_item_preserves_commentary_phase`
Michael Bolin
97dce078c5