Fix Anthropic pause_turn handling to allow agent continuation

Map Anthropic's pause_turn finish reason to None instead of 'stop' so the
agent automatically continues with a new request. This fixes issues with
long-running builtin tools like web_search that may trigger pause_turn.

When finish_reason is None, the agent treats the response as incomplete
and makes another request with the same message history, allowing the
conversation to continue seamlessly.

Fixes #2600

Author: kazmer97

pydantic_ai_slim/pydantic_ai/models/anthropic.py

@@ -42,12 +42,12 @@
 from ..tools import ToolDefinition
 from . import Model, ModelRequestParameters, StreamedResponse, check_allow_model_requests, download_item, get_user_agent
 
-_FINISH_REASON_MAP: dict[BetaStopReason, FinishReason] = {
+_FINISH_REASON_MAP: dict[BetaStopReason, FinishReason | None] = {
     'end_turn': 'stop',
     'max_tokens': 'length',
     'stop_sequence': 'stop',
     'tool_use': 'tool_call',
-    'pause_turn': 'stop',
+    'pause_turn': None,
     'refusal': 'content_filter',
 }
 

tests/models/test_anthropic.py

@@ -2723,3 +2723,12 @@ async def test_anthropic_web_search_tool_stream(allow_model_requests: None, anth
             PartDeltaEvent(index=17, delta=TextPartDelta(content_delta=' disruptions affecting North America.')),
         ]
     )
+
+
+def test_pause_turn_finish_reason_mapping():
+    """Test that pause_turn is mapped to None so the agent continues."""
+    from pydantic_ai.models.anthropic import _FINISH_REASON_MAP  # pyright: ignore[reportPrivateUsage]
+
+    assert _FINISH_REASON_MAP['pause_turn'] is None
+    assert _FINISH_REASON_MAP['end_turn'] == 'stop'
+    assert _FINISH_REASON_MAP['tool_use'] == 'tool_call'