Tests: honour turn-seam contracts in test_upgrade_cta_accept.py

## Goal Make the turn-stage fakes in `tests/core/agent_harness/session/test_upgrade_cta_accept.py` honour the contracts they replace. Two patterns to remove, both of which keep a test green when the contract changes underneath it: - a stage injected as `lambda *_a, **_k` — ignores the callable Protocol - an answer faked as `type("Run", (), {...})()` — an anonymous object with one attribute, standing in for a real result type ## Swallow-all seam stubs in this file (2) ``` 37: gather=lambda *_a, **_k: "should-not-run", 38: answer=lambda *_a, **_k: type("Run", (), {"response_text": "Draft outline."})(), ``` Each of these should take the signature its Protocol declares. `EvidenceGatherer`, for example, is `__call__(self, text: str, *, turn_plan: Any = None)` (`core/agent_harness/ports.py`), so its stub is: ```python def no_evidence(text: str, *, turn_plan: Any = None) -> GatheredEvidence | None: """An EvidenceGatherer that finds nothing.""" return None ``` Add a required keyword to the Protocol and that version fails at once; the swallow-all lambda keeps passing. ## Anonymous result objects in this file (1) ``` 38: answer=lambda *_a, **_k: type("Run", (), {"response_text": "Draft outline."})(), ``` Expected: a real `LlmRunInfo` from the shared helper, so the test fails when the type gains a field the product reads. ```python return fake_llm_run(response_text="...") ``` ## Order Depends on #5187 (shared turn-seam helpers). Wait for it to land. ## Acceptance - [ ] No `lambda *_a, **_k` passed as a stage in `tests/core/agent_harness/session/test_upgrade_cta_accept.py` - [ ] No `type("Run", ...)` result fakes in `tests/core/agent_harness/session/test_upgrade_cta_accept.py` - [ ] Stubs are named functions reusing the shared helpers - [ ] Test intent unchanged: `answer=None` means the real stage runs, a no-op stub means no answer — do not swap one for the other - [ ] `uv run pytest tests/core/agent_harness/session/test_upgrade_cta_accept.py` green, no product change ## Out of scope Other files, monkeypatch lambdas that are not stage injections, and product Protocol bodies. ## Guidelines `AGENTS.md` — Protocols as callable contracts; test fakes are named `def`s.