## Why
Multi-Agent V2 children are owned by their parent at runtime. Resuming an
unloaded child directly could rebuild it from caller-provided settings instead
of the parent's current authority.
## What changed
- Route child reloads through their loaded immediate parent and reject direct
cold resume when that parent is unavailable.
- Preserve the child's recorded model, provider, reasoning effort, and role
while inheriting the parent's execution policy and MCP extensions.
- Validate cached environments against the parent, intersect local permission
profiles, and reject stale remote or workspace-root configurations.
- Keep paginated cold-resume token usage attribution when attaching to the
reloaded child.
## Testing
Add coverage for owner validation, nested-parent reloads, permission and
environment changes, role instruction restoration, paginated usage replay,
and app-server child resume behavior.
GitOrigin-RevId: 84014762bcdb57f94fc23974c9c1af55dc1babf1
d21794d6ba