Add one-time nudge when assistant commits to edit intent without editing files

[mmprotest]

Motivation

• The runner sometimes accepts a final assistant prose turn that explicitly commits to a concrete code change but no file write/patch was performed, causing lost edits and reduced reliability.
• Provide a minimal, bounded follow-up to let the assistant apply the described minimal edit without changing runner architecture or affecting plan-only flows.

Description

• Add a conservative heuristic helper response_commits_to_code_edit(text: str) -> bool to detect explicit edit commitment while excluding suggestion/analysis phrasing (e.g., "one possible fix would be", "you could update").
• In the runner completion path, if the assistant’s final text matches the heuristic and no edit occurred, inject a single generic user nudge: "You described a concrete code change, but no file was modified. Apply the minimal edit now, then verify if possible.", then continue for one more model turn.
• Gate the behavior behind a one-time-per-run flag self._edit_intent_nudge_used and skip it in planning read-only mode to avoid affecting analysis/plan-only tasks.
• Emit a lightweight runtime event edit_intent_without_edit_nudged when the nudge is used and add unit tests for the heuristic.

Testing

• Added tests in tests/test_state_runtime.py covering positive and negative examples for response_commits_to_code_edit and ran pytest -q tests/test_state_runtime.py -k "response_commits_to_code_edit", which passed (2 passed).
• Ran full pytest -q tests/test_state_runtime.py, which passed (34 passed).
• Files changed: villani_code/state_runtime.py, villani_code/state.py, and tests/test_state_runtime.py.
• Commands run during verification: pytest -q tests/test_state_runtime.py -k "response_commits_to_code_edit" and pytest -q tests/test_state_runtime.py, both succeeded.

---

Codex Task