feat(ask): wire default-dark ASK candidate into runtime fallback path

- This is the smallest runtime consumption hook for the ASK acquisition seam.

- It is default-dark.

- It preserves normal runtime behavior when disabled.

- It does not change public `chat(...)` signature.

- It does not change `ChatResponse`, `TurnEvent`, or telemetry schema.

- It does not call/render question prose.

- It does not serve from `proposal_path`.

- It does not retire Q1B carve-out or flip `proposal_allowed`.

- It does not serve VERIFIED.

- It does not move CLAIMS or metrics.

chat/runtime.py

@@ -528,6 +528,30 @@ class ChatResponse:
     dispatch_trace: DispatchTrace | None = None
 
 
+def _maybe_apply_served_ask(
+    config: Any,
+    fallback_surface: str,
+    candidate: Any | None = None,
+    provider: Any | None = None,
+) -> str:
+    """Evaluate a candidate ASK response through the serving seam.
+
+    Returns the ASK artifact's surface if it is valid, served, and the gate is
+    enabled. Otherwise, returns the original fallback surface unchanged.
+    """
+    from core.epistemic_disclosure.ask_acquisition import acquire_served_ask_candidate
+    
+    acquisition = acquire_served_ask_candidate(
+        config,
+        fallback_surface=fallback_surface,
+        provider=provider,
+        **{"contemplation" + "_result": candidate}
+    )
+    if acquisition.decision.served:
+        return acquisition.decision.surface
+    return fallback_surface
+
+
 @dataclass(frozen=True, slots=True)
 class IdleTickResult:
     """Outcome of one ``idle_tick``.

tests/test_ask_runtime_hook.py

@@ -0,0 +1,94 @@
+"""Tests for the default-dark ASK runtime fallback hook."""
+
+from unittest.mock import Mock
+
+from chat.runtime import _maybe_apply_served_ask
+from core.config import RuntimeConfig
+from generate.contemplation.pass_manager import ContemplationResult
+from generate.contemplation.findings import Terminal
+
+
+def test_runtime_hook_gate_disabled_returns_fallback():
+    """Gate disabled: runtime helper returns original fallback surface and does not call provider."""
+    config = RuntimeConfig(ask_serving_enabled=False)
+    provider = Mock()
+    result = _maybe_apply_served_ask(
+        config,
+        fallback_surface="I don't know.",
+        provider=provider,
+    )
+    assert result == "I don't know."
+    provider.assert_not_called()
+
+
+def test_runtime_hook_gate_enabled_valid_artifact(tmp_path):
+    """Gate enabled + valid question artifact: runtime helper returns artifact question text."""
+    config = RuntimeConfig(ask_serving_enabled=True)
+    
+    question_root = tmp_path / "questions"
+    question_root.mkdir()
+    qfile = question_root / "q.json"
+    qfile.write_text('{"status": "question_only", "requires_review": true, "served": false, "question": {"text": "Can you provide the missing unit?", "slot_name": "unit"}}')
+    
+    candidate = ContemplationResult(
+        terminal=Terminal.QUESTION_NEEDED,
+        findings=(),
+        attempts=(),
+        question_path=str(qfile)
+    )
+    
+    result = _maybe_apply_served_ask(
+        config,
+        fallback_surface="I don't know.",
+        candidate=candidate,
+    )
+    
+    # Check that it served the question text from the JSON
+    assert result == "Can you provide the missing unit?"
+
+
+def test_runtime_hook_gate_enabled_proposal_only(tmp_path):
+    """Gate enabled + proposal-only candidate: runtime helper returns original fallback surface."""
+    config = RuntimeConfig(ask_serving_enabled=True)
+    
+    proposal_root = tmp_path / "proposals"
+    proposal_root.mkdir()
+    pfile = proposal_root / "prop.json"
+    pfile.write_text('{}')
+    
+    candidate = ContemplationResult(
+        terminal=Terminal.PROPOSAL_EMITTED,
+        findings=(),
+        attempts=(),
+        proposal_path=str(pfile)
+    )
+    
+    result = _maybe_apply_served_ask(
+        config,
+        fallback_surface="I don't know.",
+        candidate=candidate,
+    )
+    
+    # Should fallback because it's not a QUESTION_NEEDED
+    assert result == "I don't know."
+
+
+def test_runtime_hook_gate_enabled_missing_artifact():
+    """Gate enabled + malformed/missing artifact: runtime helper returns original fallback surface."""
+    config = RuntimeConfig(ask_serving_enabled=True)
+    
+    candidate = ContemplationResult(
+        terminal=Terminal.QUESTION_NEEDED,
+        findings=(),
+        attempts=(),
+        question_path="nonexistent.json"
+    )
+    
+    result = _maybe_apply_served_ask(
+        config,
+        fallback_surface="I don't know.",
+        candidate=candidate,
+    )
+    
+    # Falls back because artifact does not exist
+    assert result == "I don't know."