jif b705b6b076 Report completed sub-agent activity on parent turns (#40437) ...

## Why

A Multi-Agent V2 child can finish after the parent turn that spawned it, so its
successful completion needs to remain associated with that parent turn in
notifications and history.

## What changed

- Add `completed` to `SubAgentActivityKind` and emit the corresponding started
  and completed item events on the spawning parent turn when a child succeeds.
- Persist completed activity as a canonical turn item in both legacy and
  paginated history, and expose it through app-server history and schemas.
- Render completed activity as terminal in the TUI without counting it as a
  separate tool call or tool-runtime event.

## Testing

- Cover successful completion in legacy and paginated history, late updates to
  completed parent turns, TUI rendering, analytics, and rollout tracing.
- Verify that terminal child errors do not emit completed activity.

GitOrigin-RevId: 6c71eb8b10e7327611c6af84f70e294e27d94d02

2026-08-24 17:07:21 +00:00

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src

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BUILD.bazel

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Cargo.toml

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