test(providers): ladder-to-wire effort parity harness across all lanes

Proves the effort-ladder projection against the real request path
instead of against the mapping helpers it shares with it. For 22
(provider lane x capability shape) points — both Anthropic lanes,
openai-compatible on both API surfaces, openai, google (default and
template-override hybrid), xai (default and inert-override), and the
DeepSeek/qwen template contracts — every knob position is driven
through the actual provider create_streaming against a recording fake
client, and two invariants are asserted per shape:

1. each ladder token decodes to an expected effort wire subset
   (toggle / template effort / flat param / thinking budget /
   output_config) that must equal the captured kwargs exactly;
2. two knob positions carry equal tokens iff they produce identical
   effort-relevant wire payloads — the grouping promise the UI
   annotations lean on.

The RecordingClient SDK-seam stub moves from the wire-payload golden
harness into tests/_wire_capture.py so both suites capture at the same
seam. Verified the harness catches the bug class it was built for:
re-adding xai to _CHAT_LANES fails xai-template-override-inert.

tests/_wire_capture.py

@@ -0,0 +1,76 @@
+"""Recording fake SDK client — captures the kwargs at each provider's seam.
+
+Every provider's ``create_streaming`` assembles its kwargs and calls the
+SDK *eagerly* before returning the stream iterator (Anthropic
+``client.messages.stream``, OpenAI ``client.chat.completions.create``,
+Responses ``client.responses.create/stream``), so driving a provider
+against a :class:`RecordingClient` captures the full composed request
+payload without a network round-trip.
+
+Shared by the wire-payload golden harness (``test_wire_payload_golden``)
+and the effort-ladder parity harness (``test_effort_ladder_wire_parity``)
+so both assert against the same capture seam.
+"""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Any
+
+if TYPE_CHECKING:
+    from collections.abc import Iterator
+
+
+class _EmptyStream:
+    """Stand-in for an SDK stream / stream-manager: empty iterable AND no-op CM."""
+
+    def __iter__(self) -> Iterator[Any]:
+        return iter(())
+
+    def __enter__(self) -> _EmptyStream:
+        return self
+
+    def __exit__(self, *exc: object) -> None:
+        return None
+
+
+class _Seam:
+    """Records the kwargs of a single SDK call, returns an empty stream stub."""
+
+    def __init__(self, sink: dict[str, Any]) -> None:
+        self._sink = sink
+
+    def __call__(self, **kwargs: Any) -> _EmptyStream:
+        # Last write wins; only one seam is exercised per provider call.
+        self._sink["payload"] = kwargs
+        return _EmptyStream()
+
+
+class _Completions:
+    def __init__(self, sink: dict[str, Any]) -> None:
+        self.create = _Seam(sink)
+
+
+class _Chat:
+    def __init__(self, sink: dict[str, Any]) -> None:
+        self.completions = _Completions(sink)
+
+
+class _Messages:
+    def __init__(self, sink: dict[str, Any]) -> None:
+        self.stream = _Seam(sink)
+
+
+class _Responses:
+    def __init__(self, sink: dict[str, Any]) -> None:
+        self.create = _Seam(sink)
+        self.stream = _Seam(sink)
+
+
+class RecordingClient:
+    """Fake SDK client exposing every provider's call seam, recording kwargs."""
+
+    def __init__(self) -> None:
+        self.captured: dict[str, Any] = {}
+        self.messages = _Messages(self.captured)
+        self.chat = _Chat(self.captured)
+        self.responses = _Responses(self.captured)