test(agent): expand coverage and refactor test structure

- Add 42 tests for ContextBuilder (context.py: 0→42 tests)
- Add 37 tests for SubagentManager lifecycle (subagent.py: 2→37 tests)
- Add 42 unit tests for AutoCompact in isolation
- Split monolithic test_runner.py (3313 lines) into 9 focused files:
  test_runner_core, test_runner_hooks, test_runner_errors,
  test_runner_safety, test_runner_persistence, test_runner_governance,
  test_runner_tool_execution, test_runner_injections,
  test_loop_runner_integration
- Add 3 config passthrough tests (temperature/max_tokens/reasoning_effort)
- Fix fragile patch.object(__init__) in test_stop_preserves_context
- Create shared conftest.py with make_provider/make_loop factories

Total: 934 tests passing, 0 regressions

tests/agent/test_runner_hooks.py

@@ -0,0 +1,172 @@
+"""Tests for AgentRunner hook lifecycle: ordering, streaming deltas,
+cached-token propagation, and hook context."""
+
+from __future__ import annotations
+
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+from nanobot.config.schema import AgentDefaults
+from nanobot.providers.base import LLMProvider, LLMResponse, ToolCallRequest
+
+_MAX_TOOL_RESULT_CHARS = AgentDefaults().max_tool_result_chars
+
+
+@pytest.mark.asyncio
+async def test_runner_calls_hooks_in_order():
+    from nanobot.agent.hook import AgentHook, AgentHookContext
+    from nanobot.agent.runner import AgentRunSpec, AgentRunner
+
+    provider = MagicMock(spec=LLMProvider)
+    call_count = {"n": 0}
+    events: list[tuple] = []
+
+    async def chat_with_retry(**kwargs):
+        call_count["n"] += 1
+        if call_count["n"] == 1:
+            return LLMResponse(
+                content="thinking",
+                tool_calls=[ToolCallRequest(id="call_1", name="list_dir", arguments={"path": "."})],
+            )
+        return LLMResponse(content="done", tool_calls=[], usage={})
+
+    provider.chat_with_retry = chat_with_retry
+    tools = MagicMock()
+    tools.get_definitions.return_value = []
+    tools.execute = AsyncMock(return_value="tool result")
+
+    class RecordingHook(AgentHook):
+        async def before_iteration(self, context: AgentHookContext) -> None:
+            events.append(("before_iteration", context.iteration))
+
+        async def before_execute_tools(self, context: AgentHookContext) -> None:
+            events.append((
+                "before_execute_tools",
+                context.iteration,
+                [tc.name for tc in context.tool_calls],
+            ))
+
+        async def after_iteration(self, context: AgentHookContext) -> None:
+            events.append((
+                "after_iteration",
+                context.iteration,
+                context.final_content,
+                list(context.tool_results),
+                list(context.tool_events),
+                context.stop_reason,
+            ))
+
+        def finalize_content(self, context: AgentHookContext, content: str | None) -> str | None:
+            events.append(("finalize_content", context.iteration, content))
+            return content.upper() if content else content
+
+    runner = AgentRunner(provider)
+    result = await runner.run(AgentRunSpec(
+        initial_messages=[],
+        tools=tools,
+        model="test-model",
+        max_iterations=3,
+        max_tool_result_chars=_MAX_TOOL_RESULT_CHARS,
+        hook=RecordingHook(),
+    ))
+
+    assert result.final_content == "DONE"
+    assert events == [
+        ("before_iteration", 0),
+        ("before_execute_tools", 0, ["list_dir"]),
+        (
+            "after_iteration",
+            0,
+            None,
+            ["tool result"],
+            [{"name": "list_dir", "status": "ok", "detail": "tool result"}],
+            None,
+        ),
+        ("before_iteration", 1),
+        ("finalize_content", 1, "done"),
+        ("after_iteration", 1, "DONE", [], [], "completed"),
+    ]
+
+
+@pytest.mark.asyncio
+async def test_runner_streaming_hook_receives_deltas_and_end_signal():
+    from nanobot.agent.hook import AgentHook, AgentHookContext
+    from nanobot.agent.runner import AgentRunSpec, AgentRunner
+
+    provider = MagicMock(spec=LLMProvider)
+    streamed: list[str] = []
+    endings: list[bool] = []
+
+    async def chat_stream_with_retry(*, on_content_delta, **kwargs):
+        await on_content_delta("he")
+        await on_content_delta("llo")
+        return LLMResponse(content="hello", tool_calls=[], usage={})
+
+    provider.chat_stream_with_retry = chat_stream_with_retry
+    provider.chat_with_retry = AsyncMock()
+    tools = MagicMock()
+    tools.get_definitions.return_value = []
+
+    class StreamingHook(AgentHook):
+        def wants_streaming(self) -> bool:
+            return True
+
+        async def on_stream(self, context: AgentHookContext, delta: str) -> None:
+            streamed.append(delta)
+
+        async def on_stream_end(self, context: AgentHookContext, *, resuming: bool) -> None:
+            endings.append(resuming)
+
+    runner = AgentRunner(provider)
+    result = await runner.run(AgentRunSpec(
+        initial_messages=[],
+        tools=tools,
+        model="test-model",
+        max_iterations=1,
+        max_tool_result_chars=_MAX_TOOL_RESULT_CHARS,
+        hook=StreamingHook(),
+    ))
+
+    assert result.final_content == "hello"
+    assert streamed == ["he", "llo"]
+    assert endings == [False]
+    provider.chat_with_retry.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_runner_passes_cached_tokens_to_hook_context():
+    """Hook context.usage should contain cached_tokens."""
+    from nanobot.agent.hook import AgentHook, AgentHookContext
+    from nanobot.agent.runner import AgentRunSpec, AgentRunner
+
+    provider = MagicMock(spec=LLMProvider)
+    captured_usage: list[dict] = []
+
+    class UsageHook(AgentHook):
+        async def after_iteration(self, context: AgentHookContext) -> None:
+            captured_usage.append(dict(context.usage))
+
+    async def chat_with_retry(**kwargs):
+        return LLMResponse(
+            content="done",
+            tool_calls=[],
+            usage={"prompt_tokens": 200, "completion_tokens": 20, "cached_tokens": 150},
+        )
+
+    provider.chat_with_retry = chat_with_retry
+    tools = MagicMock()
+    tools.get_definitions.return_value = []
+
+    runner = AgentRunner(provider)
+    await runner.run(AgentRunSpec(
+        initial_messages=[],
+        tools=tools,
+        model="test-model",
+        max_iterations=1,
+        max_tool_result_chars=_MAX_TOOL_RESULT_CHARS,
+        hook=UsageHook(),
+    ))
+
+    assert len(captured_usage) == 1
+    assert captured_usage[0]["cached_tokens"] == 150