test: freeze tool-call contract semantics

Lock the current Anthropic streaming asymmetry so future refactors do not silently synthesize tool blocks. Align schema and docs with the actual support level to avoid over-promising forced-tool fallback.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/test_tool_call_bridge.py

@@ -662,6 +662,43 @@ class ToolCallBridgeTests(unittest.IsolatedAsyncioTestCase):
         self.assertIn('"type": "tool_use"', body)
         self.assertIn('"stop_reason": "tool_use"', body)
 
+    async def test_anthropic_stream_does_not_fallback_to_synthetic_tool_blocks_for_forced_tool(self) -> None:
+        fake_client = _FakeClient(
+            stream_events=[
+                {"type": "text", "text": '```json\n{"input": {"k": "v"}, "result": {"value": 1}}\n```'}
+            ],
+            complete_result={},
+        )
+        req = AnthropicMessagesRequest(
+            model="claude-3-5-sonnet-20241022",
+            max_tokens=256,
+            messages=[{"role": "user", "content": "hi"}],
+            stream=True,
+            tools=[{"name": "lookup", "input_schema": {"type": "object", "properties": {}}}],
+            tool_choice={"type": "tool", "name": "lookup"},
+        )
+
+        with (
+            patch.object(main, "pool", _FakePool(_FakeInstance(fake_client))),
+            patch.object(main, "chat_guard", _FakeGuard()),
+            patch.object(main, "_ensure_instance_logged_in", AsyncMock(return_value={"id": "u"})),
+            patch.object(main.stats_collector, "record_chat", AsyncMock(return_value=None)),
+            patch.object(main.settings, "api_keys", ["test-key"]),
+        ):
+            response = await main.v1_messages(
+                req,
+                _make_request(
+                    "/v1/messages",
+                    headers={"x-api-key": "test-key", "anthropic-version": "2023-06-01"},
+                ),
+            )
+            body = await _collect_stream(response)
+
+        self.assertNotIn('"type": "tool_use"', body)
+        self.assertNotIn('"type": "tool_result"', body)
+        self.assertIn('"type": "text_delta"', body)
+        self.assertIn('"stop_reason": "end_turn"', body)
+
     async def test_anthropic_stream_bridges_tool_and_text_events(self) -> None:
         fake_client = _FakeClient(
             stream_events=[