Stack split from #25708. Original PR intentionally left open. This third
PR resolves the effective per-thread multi-agent runtime from persisted
metadata, inherited runtime, and current model selection.
## Summary
- default multi-agent v2 to direct-model-only tools so code mode does
not wrap subagent tools
- add default root/subagent team prompts aligned with dogfood training
assumptions
- tighten spawn-agent model override wording to prefer the inherited
model by default
## Tests
- just fmt
- just test -p codex-core
spawn_agent_description_lists_visible_models_and_reasoning_efforts
- just test -p codex-core
multi_agent_v2_default_session_thread_cap_counts_root
- just test -p codex-rollout-trace
- just fix -p codex-core
- just fix -p codex-rollout-trace
Note: a broad just test -p codex-core run was attempted locally, but
this sandbox produced unrelated environment failures around
sandbox-exec, missing test_stdio_server, and realtime timeouts.
## Why
Phase 2 still needs to choose the most relevant stage-1 memory outputs
by usage and recency, but exposing that ranking as the rendered
`raw_memories.md` order creates unnecessary large diff. Usage-count or
timestamp changes can reshuffle otherwise unchanged memories, making the
workspace diff noisy and giving the consolidation prompt a misleading
recency signal from file position.
This fix will reduce token consumption
## What Changed
- Keep the existing top-N Phase 2 selection ranking by `usage_count`,
`last_usage`, `source_updated_at`, and `thread_id`.
- Return the selected rows in stable ascending `thread_id` order before
syncing Phase 2 filesystem inputs.
- Update the memory README, raw memories header, and consolidation
prompt so they describe the stable order and tell the prompt to use
metadata and workspace diffs instead of file order as the recency
signal.
- Adjust the memory runtime tests to use deterministic thread IDs and
assert the stable return order separately from the ranked selection
semantics.
## Test Coverage
- Existing memory runtime tests in
`codex-rs/state/src/runtime/memories.rs` now cover the stable returned
ordering for Phase 2 inputs.
---------
Co-authored-by: Codex <noreply@openai.com>
## Why
MultiAgentV2 sessions need startup guidance that matches the role of the
thread that is actually being created. Root agents and subagents have
different responsibilities, and forked subagents can inherit parent
rollout history. If the parent hint is carried into the child context,
the child can see stale or conflicting developer guidance before its own
session-specific context is added.
## What changed
- Added `features.multi_agent_v2.root_agent_usage_hint_text` and
`features.multi_agent_v2.subagent_usage_hint_text` config fields,
including schema/config parsing support.
- Injected the matching root or subagent hint into the initial context
as its own developer message when `multi_agent_v2` is enabled.
- Filtered configured MultiAgentV2 usage-hint developer messages out of
forked parent history so a child thread receives fresh guidance for its
own session source/config.
- Added targeted coverage for config parsing, initial-context rendering,
feature-config deserialization, and forked-history filtering.
## Context examples
With this config:
```toml
[features.multi_agent_v2]
enabled = true
root_agent_usage_hint_text = "Root guidance."
subagent_usage_hint_text = "Subagent guidance."
```
A root thread initial context renders the root hint as a standalone
developer message:
```text
[developer]
<existing developer context, when present>
[developer]
Root guidance.
```
A subagent thread initial context renders the subagent hint instead:
```text
[developer]
<existing developer context, when present>
[developer]
Subagent guidance.
```
When a subagent forks parent history, any parent developer message whose
text exactly matches the configured MultiAgentV2 root or subagent hint
is omitted from the forked history before the child receives its fresh
subagent hint.
jif-oaiandGitHub
