## Why
Multi-agent v2 residency is intended to keep only the threads that need
to be live. The existing rollout resume path still walked persisted open
descendants and reopened the entire descendant tree when resuming a v2
root, which turns resume into an eager reload of work that should stay
unloaded until it is explicitly needed.
The interrupted-agent path has a related residency issue. Interrupted
agents remain open by design, so an idle interrupted resident should be
eligible for eviction just like an idle completed or errored resident.
Otherwise a resident set full of interrupted agents can consume every v2
slot and block later spawns or reloads with `AgentLimitReached`.
## What Changed
- Return early from `resume_agent_from_rollout` after resuming a v2
thread so persisted v2 descendants are not reopened eagerly.
- Treat idle `Interrupted` v2 residents as unloadable in the LRU
residency path.
- Add focused coverage for v2 root resume leaving descendants unloaded
and for eviction of an idle interrupted v2 resident when a new slot is
needed.
## Verification
Added targeted `codex-core` tests covering:
- v2 root resume with persisted descendants, verifying only the root is
loaded after resume.
- residency eviction of an idle interrupted v2 agent when the resident
set is full.
jif
0526cb56ac