Enforce the tool-call contract, asking servers only where it works

The executor ended a milestone on any reply without a tool call, and
nothing held a model to the offered tools. Measured on the 4070:
tool_choice "required" is enforced by vLLM (local-fast) and Anthropic,
but qwen3-14b (local-coder) under it cannot stop and writes until the
output ceiling, a known model bug. So enforcement is asked for per
model, and the loop holds the contract itself everywhere.

- The catalog reads supports_tool_choice from LiteLLM's model_info;
  BudgetedClient sends tool_choice only to models declared true, as
  "required" on the normalized route and {"type": "any"} on the
  Anthropic passthrough, and only when tools are offered
- The executor gains an explicit finish tool, the only way to end a
  milestone. Finishing with nothing changed is refused once; a prose
  reply gets one nudge, then escalates; a call to a tool not offered
  counts toward failure_limit, like a failed command; calls after
  finish are recorded as not run
- Clients record the model that actually answered. ModelFacts.answered
  recognises a proxy fallback, which once credited Claude's answers to
  a local model that could not call tools at all
- The context probe reports a fallback instead of trusting it; rerun,
  both local models now refuse over-long prompts, as they should
- The capability matrix checks every answer came from the model asked,
  that models call only offered tools, and that a declared
  supports_tool_choice is true
- Spec A15 and the tuning guide say how enforcement is requested,
  declared and backed up

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

nisse-dev/src/nisse_dev/cancel.py

@@ -29,10 +29,12 @@ class Cancel:
         return self._event.is_set()
 
 
-def skip_calls(store: StateStore, calls: list[ToolCall]) -> None:
-    """Record the calls a stop left unrun. Every tool call needs a result for
-    the transcript to render again, and the result says what happened."""
+def skip_calls(
+    store: StateStore, calls: list[ToolCall], reason: str = STOPPED_RESULT
+) -> None:
+    """Record calls left unrun. Every tool call needs a result for the
+    transcript to render again, and the result says what happened."""
     for call in calls:
         store.append_event(
-            ToolResult(call_id=call.call_id, result=STOPPED_RESULT, success=False)
+            ToolResult(call_id=call.call_id, result=reason, success=False)
         )