feat(checkpoint): add pre-compression checkpoint flush hook

tests/test_checkpoint_flush.py

@@ -0,0 +1,39 @@
+"""Test that flush_checkpoint is called during context compression."""
+import json
+import pytest
+from unittest.mock import MagicMock
+
+
+def test_flush_checkpoint_method_exists():
+    """AIAgent must have a flush_checkpoint method."""
+    from run_agent import AIAgent
+    assert hasattr(AIAgent, "flush_checkpoint")
+
+
+def test_flush_checkpoint_writes_to_store(tmp_path):
+    """flush_checkpoint should write a checkpoint with current session state."""
+    from agent.checkpoint_store import CheckpointStore
+    from tools.checkpoint_tool import checkpoint_tool
+    store = CheckpointStore(checkpoints_dir=tmp_path / "checkpoints")
+
+    mock_agent = MagicMock()
+    mock_agent.session_id = "flush_test_session"
+    mock_agent._checkpoint_store = store
+    mock_agent._todo_store = MagicMock()
+    mock_agent._todo_store.format_for_injection.return_value = "- [x] Step 1"
+
+    # Verify the checkpoint tool writes successfully (same path flush_checkpoint uses)
+    result = checkpoint_tool(
+        action="write",
+        task="Auto-checkpoint before compression",
+        progress=[],
+        state={},
+        decisions=[],
+        store=store,
+        agent=mock_agent,
+    )
+    data = json.loads(result)
+    assert data["success"] is True
+    saved = store.read("flush_test_session")
+    assert saved is not None
+    assert saved["task"] == "Auto-checkpoint before compression"