Add Phase 7: polish and hardening — retry, truncation, sessions, shutdown

- Config extensions: retry backoff, truncation threshold, session persistence
- LLM retry with exponential backoff + jitter on transient errors (5xx, connection)
- Conversation truncation: drops oldest messages preserving first user + recent N
- Session persistence: auto-save/restore with atomic writes, cleanup of old files
- Graceful shutdown: SIGTERM handler, cancel() on AgentLoop, save-on-exit
- Partial message recovery on mid-stream interruption
- New slash commands: /save, /session
- 18 new tests (5 retry, 5 truncation, 4 session, 4 integration workflows)
- README.md and docs/tools.md documentation

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

tests/unit/test_retry.py

@@ -0,0 +1,125 @@
+"""Unit tests for LLM retry with exponential backoff."""
+
+from unittest.mock import AsyncMock, patch
+
+import pytest
+
+from app.models.config import LLMConfig
+from app.models.message import Message
+from app.services.llm import LLMClient, LLMConnectionError, LLMResponseError
+
+
+@pytest.fixture
+def llm_config() -> LLMConfig:
+    return LLMConfig(
+        model="test-model",
+        endpoint="http://localhost:11434",
+        max_retries=3,
+        retry_backoff_base=0.01,
+        retry_backoff_max=0.05,
+    )
+
+
+@pytest.fixture
+def client(llm_config: LLMConfig) -> LLMClient:
+    return LLMClient(llm_config)
+
+
+@pytest.fixture
+def messages() -> list[Message]:
+    return [Message(role="user", content="Hello")]
+
+
+class TestRetry:
+    @pytest.mark.asyncio
+    async def test_succeeds_without_retry(self, client: LLMClient, messages: list[Message]) -> None:
+        """Successful stream doesn't retry."""
+        call_count = 0
+
+        async def fake_stream(*args, **kwargs):
+            nonlocal call_count
+            call_count += 1
+            yield {"choices": [{"delta": {"content": "Hi"}}]}
+
+        client.stream_chat = fake_stream  # type: ignore[assignment]
+
+        collected = []
+        async for chunk in client.stream_chat_with_retry(messages):
+            collected.append(chunk)
+
+        assert len(collected) == 1
+        assert call_count == 1
+
+    @pytest.mark.asyncio
+    async def test_retries_on_connection_error(self, client: LLMClient, messages: list[Message]) -> None:
+        """Retries on LLMConnectionError, then succeeds."""
+        call_count = 0
+
+        async def flaky_stream(*args, **kwargs):
+            nonlocal call_count
+            call_count += 1
+            if call_count < 3:
+                raise LLMConnectionError("Connection refused")
+            yield {"choices": [{"delta": {"content": "OK"}}]}
+
+        client.stream_chat = flaky_stream  # type: ignore[assignment]
+
+        with patch("app.services.llm.asyncio.sleep", new_callable=AsyncMock):
+            collected = []
+            async for chunk in client.stream_chat_with_retry(messages):
+                collected.append(chunk)
+
+        assert len(collected) == 1
+        assert call_count == 3
+
+    @pytest.mark.asyncio
+    async def test_retries_on_5xx(self, client: LLMClient, messages: list[Message]) -> None:
+        """Retries on 5xx LLMResponseError."""
+        call_count = 0
+
+        async def server_error_stream(*args, **kwargs):
+            nonlocal call_count
+            call_count += 1
+            if call_count < 2:
+                raise LLMResponseError("Internal Server Error", status_code=500)
+            yield {"choices": [{"delta": {"content": "OK"}}]}
+
+        client.stream_chat = server_error_stream  # type: ignore[assignment]
+
+        with patch("app.services.llm.asyncio.sleep", new_callable=AsyncMock):
+            collected = []
+            async for chunk in client.stream_chat_with_retry(messages):
+                collected.append(chunk)
+
+        assert len(collected) == 1
+        assert call_count == 2
+
+    @pytest.mark.asyncio
+    async def test_no_retry_on_4xx(self, client: LLMClient, messages: list[Message]) -> None:
+        """Does NOT retry on 4xx errors — raises immediately."""
+        async def bad_request_stream(*args, **kwargs):
+            raise LLMResponseError("Bad Request", status_code=400)
+            yield  # pragma: no cover — make this an async generator
+
+        client.stream_chat = bad_request_stream  # type: ignore[assignment]
+
+        with pytest.raises(LLMResponseError, match="Bad Request"):
+            async for _ in client.stream_chat_with_retry(messages):
+                pass  # pragma: no cover
+
+    @pytest.mark.asyncio
+    async def test_respects_max_retries(self, client: LLMClient, messages: list[Message]) -> None:
+        """After exhausting retries, re-raises the last exception."""
+        async def always_fail(*args, **kwargs):
+            raise LLMConnectionError("Down forever")
+            yield  # pragma: no cover
+
+        client.stream_chat = always_fail  # type: ignore[assignment]
+
+        with patch("app.services.llm.asyncio.sleep", new_callable=AsyncMock) as mock_sleep:
+            with pytest.raises(LLMConnectionError, match="Down forever"):
+                async for _ in client.stream_chat_with_retry(messages):
+                    pass  # pragma: no cover
+
+        # Should have slept max_retries times (3 retries after initial attempt)
+        assert mock_sleep.call_count == 3