chore(pydantic-ai): type/lint/back-compat fixes

Fix 22 pyright errors introduced in PR 4's new test files:
- isinstance narrowing before union-member attribute access (ToolRequestDelta.arguments_delta,
  TextDelta.text_delta, ToolResponseContent.content, FunctionToolResultEvent.part.content)
- reportReturnType in _run_yield_turn: hoist result variable out of async-with
- reportImplicitOverride on _RecordingTracer.handle: add @OverRide
- reportMissingImports in conformance tests: switch absolute tests.lib... imports to
  relative .runner imports so pyright's executionEnvironments root matches

All 230 tests pass on 3.12 and 3.13. Ruff: clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: declan-scale

tests/lib/adk/test_pydantic_ai_turn.py

@@ -276,6 +276,7 @@ async def test_default_off_matches_bare_converter_for_streamed_tool_call(self):
             e for e in turn_out if isinstance(e, StreamTaskMessageDelta) and isinstance(e.delta, ToolRequestDelta)
         ]
         assert len(deltas) == 1, "streamed tool-call args must surface as a ToolRequestDelta when coalesce is off"
+        assert isinstance(deltas[0].delta, ToolRequestDelta)
         assert deltas[0].delta.arguments_delta == '{"city":"Paris"}'
 
     async def test_coalesce_on_emits_single_full_with_accumulated_args_and_no_delta(self):

tests/lib/core/harness/conformance/test_conformance.py

@@ -40,7 +40,8 @@
 from agentex.types.tool_request_content import ToolRequestContent
 from agentex.types.tool_response_content import ToolResponseContent
 from agentex.types.reasoning_content_delta import ReasoningContentDelta
-from tests.lib.core.harness.conformance.runner import (
+
+from .runner import (
     Fixture,
     register,
     derive_all,

tests/lib/core/harness/conformance/test_pydantic_ai_conformance.py

@@ -39,13 +39,14 @@
     FunctionToolResultEvent,
 )
 
-from tests.lib.core.harness.conformance.runner import (
+from agentex.lib.adk._modules._pydantic_ai_turn import PydanticAITurn
+
+from .runner import (
     Fixture,
     register,
     derive_all,
     run_cross_channel_conformance,
 )
-from agentex.lib.adk._modules._pydantic_ai_turn import PydanticAITurn
 
 # ---------------------------------------------------------------------------
 # Helpers

tests/lib/core/harness/test_harness_pydantic_ai_async.py

@@ -265,6 +265,7 @@ async def test_tool_response_content(self) -> None:
 
         tool_resps = [m for m in fake_streaming.messages_opened if isinstance(m, ToolResponseContent)]
         assert len(tool_resps) == 1, "Expected exactly one ToolResponseContent"
+        assert isinstance(tool_resps[0].content, str)
         assert "72F" in tool_resps[0].content
         assert tool_resps[0].name == "get_weather"
 

tests/lib/core/harness/test_harness_pydantic_ai_sync.py

@@ -31,12 +31,13 @@
 
 from __future__ import annotations
 
-from typing import Any
+from typing import Any, override
 
 import pytest
 from pydantic_ai import Agent
 from pydantic_ai.models.test import TestModel
 
+from agentex.types.text_delta import TextDelta
 from agentex.lib.core.harness.types import OpenSpan, CloseSpan
 from agentex.lib.core.harness.tracer import SpanTracer
 from agentex.lib.core.harness.emitter import UnifiedEmitter
@@ -128,6 +129,7 @@ async def _run_yield_turn(
             tracing=fake_tracing,
         )
 
+    events: list[Any] = []
     async with agent.run_stream_events(user_msg) as stream:
         turn = PydanticAITurn(stream, model="test")
         emitter = UnifiedEmitter(
@@ -136,7 +138,8 @@ async def _run_yield_turn(
             parent_span_id=parent_span_id,
             tracer=tracer if tracer is not None else False,
         )
-        return [ev async for ev in emitter.yield_turn(turn)]
+        events = [ev async for ev in emitter.yield_turn(turn)]
+    return events
 
 
 # ---------------------------------------------------------------------------
@@ -208,6 +211,7 @@ async def test_tool_response_carries_weather_result(self) -> None:
         assert len(full_events) >= 1, "Expected at least one tool_response Full event"
         tool_response = full_events[0].content
         assert isinstance(tool_response, ToolResponseContent)
+        assert isinstance(tool_response.content, str)
         assert "72F" in tool_response.content
         assert tool_response.name == "get_weather"
 
@@ -221,7 +225,7 @@ async def test_accumulated_text_matches_model_output(self) -> None:
         accumulated = "".join(
             ev.delta.text_delta
             for ev in events
-            if isinstance(ev, StreamTaskMessageDelta) and hasattr(ev.delta, "text_delta") and ev.delta.text_delta
+            if isinstance(ev, StreamTaskMessageDelta) and isinstance(ev.delta, TextDelta) and ev.delta.text_delta
         )
         assert accumulated == "The weather in Paris is sunny and 72F."
 
@@ -336,6 +340,7 @@ async def test_span_signal_types(self) -> None:
         received_signals: list[Any] = []
 
         class _RecordingTracer(RealTracer):
+            @override
             async def handle(self, signal: Any) -> None:
                 received_signals.append(signal)
                 await super().handle(signal)

tests/lib/core/harness/test_harness_pydantic_ai_temporal.py

@@ -257,6 +257,7 @@ async def test_tool_response_contains_weather_result(self) -> None:
 
         tool_resps = [m for m in fake_streaming.messages_opened if isinstance(m, ToolResponseContent)]
         assert len(tool_resps) == 1
+        assert isinstance(tool_resps[0].content, str)
         assert "72F" in tool_resps[0].content
         assert tool_resps[0].name == "get_weather"
 
@@ -328,6 +329,7 @@ async def test_run_stream_events_contains_tool_result(self) -> None:
 
         tool_results = [ev for ev in events if isinstance(ev, FunctionToolResultEvent)]
         assert len(tool_results) >= 1
+        assert isinstance(tool_results[0].part.content, str)
         assert "72F" in tool_results[0].part.content