test: 2 delegate tests fail because 'Agent' alias is recorded as action instead of canonical 'delegate_agent'

[manolitnora]

Repro

```
git checkout main
pytest tests/test_agent_runtime.py::AgentRuntimeTests::test_agent_can_delegate_to_nested_agent
pytest tests/test_agent_runtime.py::AgentRuntimeTests::test_agent_can_delegate_with_topological_batches
```

Both fail on origin/main alone (no local changes).

Symptom

```
AssertionError: 'Agent' != 'delegate_agent'

• Agent

• delegate_agent
  ```

Root cause

Origin/main introduced `'Agent'` as an alias for `'delegate_agent'` in the tool dispatch path (`src/agent_runtime.py` around line 1258 in current main: `if tool_call.name in ('Agent', 'delegate_agent')`). When the alias `'Agent'` is the actual tool name used by the model, the action recorded in metadata / file_history is `'Agent'`, but the tests assert the canonical `'delegate_agent'`.

Two fixes possible

1. Test-side: update `test_agent_can_delegate_to_nested_agent` and `test_agent_can_delegate_with_topological_batches` to accept either alias (`metadata.get('action') in ('Agent', 'delegate_agent')`).
2. Source-side: normalize the recorded action to the canonical form (`'delegate_agent'`) regardless of which alias the model used. Probably the right call since the alias is a model-facing convenience, not a runtime-state distinction.

Why I'm filing

Hit this while verifying merge-conflict resolutions on a feature branch (PR #32). Failures reproduce on pure origin/main with no local changes, so they're not from my work.