anthropic: Match other providers format for provider_metadata

src/ai/providers/anthropic/protocol.py

@@ -40,7 +40,14 @@
 
 
 def _provider_metadata(**values: Any) -> dict[str, Any]:
-    return {"provider": PROVIDER_NAME, **values}
+    """Namespace metadata as ``{"anthropic": {...}}``."""
+    return {PROVIDER_NAME: {**values}}
+
+
+def _anthropic_metadata(pm: dict[str, Any] | None) -> dict[str, Any]:
+    """Read back the metadata written by :func:`_provider_metadata`."""
+    meta = (pm or {}).get(PROVIDER_NAME)
+    return meta if isinstance(meta, dict) else {}
 
 
 # ---------------------------------------------------------------------------
@@ -207,9 +214,9 @@ async def _messages_to_anthropic(
                             text=text,
                             provider_metadata=provider_metadata,
                         ):
-                            signature = (provider_metadata or {}).get(
-                                "signature"
-                            )
+                            signature = _anthropic_metadata(
+                                provider_metadata
+                            ).get("signature")
                             if signature:
                                 content.append(
                                     {
@@ -252,7 +259,9 @@ async def _messages_to_anthropic(
                             # Result block type comes from the original wire
                             # event ("web_search_tool_result", etc.); stored in
                             # provider metadata when emitted.
-                            part_metadata = part.provider_metadata or {}
+                            part_metadata = _anthropic_metadata(
+                                part.provider_metadata
+                            )
                             wire_type = (
                                 part_metadata.get("resultType")
                                 or f"{part.tool_name}_tool_result"

tests/providers/anthropic/test_adapter.py

@@ -127,10 +127,7 @@ async def test_reasoning_signature_round_trips_from_provider_metadata(
                 ai.assistant_message(
                     ai.thinking(
                         "hidden",
-                        provider_metadata={
-                            "provider": "anthropic",
-                            "signature": "sig",
-                        },
+                        provider_metadata={"anthropic": {"signature": "sig"}},
                     )
                 ),
                 ai.user_message("Hi"),
@@ -161,15 +158,14 @@ async def test_builtin_tool_parts_round_trip(
         tool_call_id="srvtoolu_1",
         tool_name="web_search",
         tool_args='{"query":"weather"}',
-        provider_metadata={"provider": "anthropic"},
+        provider_metadata={"anthropic": {}},
     )
     result = messages.BuiltinToolReturnPart(
         tool_call_id="srvtoolu_1",
         tool_name="web_search",
         result=[{"title": "Forecast", "url": "https://example.com"}],
         provider_metadata={
-            "provider": "anthropic",
-            "resultType": "web_search_tool_result",
+            "anthropic": {"resultType": "web_search_tool_result"},
         },
     )
     convo = [

tests/providers/anthropic/test_stream.py

@@ -65,7 +65,7 @@ async def test_server_tool_use_emits_builtin_events(
     assert calls[0].tool_call_id == "srvtoolu_1"
     assert calls[0].tool_name == "web_search"
     assert calls[0].tool_args == '{"query":"weather"}'
-    assert calls[0].provider_metadata == {"provider": "anthropic"}
+    assert calls[0].provider_metadata == {"anthropic": {}}
 
 
 async def test_tool_result_block_emits_builtin_result(
@@ -102,8 +102,7 @@ async def test_tool_result_block_emits_builtin_result(
     assert ret.tool_name == "web_search"
     assert ret.result == payload
     assert ret.provider_metadata == {
-        "provider": "anthropic",
-        "resultType": "web_search_tool_result",
+        "anthropic": {"resultType": "web_search_tool_result"},
     }
 
 
@@ -120,10 +119,7 @@ async def test_signature_delta_emits_provider_metadata(
 
     reasoning = s.message.parts[0]
     assert isinstance(reasoning, messages.ReasoningPart)
-    assert reasoning.provider_metadata == {
-        "provider": "anthropic",
-        "signature": "sig",
-    }
+    assert reasoning.provider_metadata == {"anthropic": {"signature": "sig"}}
 
 
 async def test_event_kinds_in_order(monkeypatch: pytest.MonkeyPatch) -> None: