fix: harden compaction pair handling

tests/test_compaction_tool_pairs.py

@@ -0,0 +1,189 @@
+import importlib.util
+import os
+import sys
+import tempfile
+import types
+import unittest
+from pathlib import Path
+
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+MODULES = {
+    "s08": REPO_ROOT / "s08_context_compact" / "code.py",
+    "s09": REPO_ROOT / "s09_memory" / "code.py",
+    "s20": REPO_ROOT / "s20_comprehensive" / "code.py",
+}
+
+
+def load_module(name: str, path: Path, temp_cwd: Path):
+    fake_anthropic = types.ModuleType("anthropic")
+
+    class FakeAnthropic:
+        def __init__(self, *args, **kwargs):
+            self.messages = types.SimpleNamespace(create=None)
+
+    fake_dotenv = types.ModuleType("dotenv")
+    setattr(fake_anthropic, "Anthropic", FakeAnthropic)
+    setattr(fake_dotenv, "load_dotenv", lambda override=True: None)
+
+    previous_anthropic = sys.modules.get("anthropic")
+    previous_dotenv = sys.modules.get("dotenv")
+    previous_cwd = Path.cwd()
+    previous_model = os.environ.get("MODEL_ID")
+    previous_key = os.environ.get("ANTHROPIC_API_KEY")
+
+    spec = importlib.util.spec_from_file_location(name, path)
+    if spec is None or spec.loader is None:
+        raise RuntimeError(f"Unable to load {path}")
+    module = importlib.util.module_from_spec(spec)
+
+    sys.modules["anthropic"] = fake_anthropic
+    sys.modules["dotenv"] = fake_dotenv
+    os.environ["MODEL_ID"] = "test-model"
+    os.environ["ANTHROPIC_API_KEY"] = "test-key"
+    try:
+        os.chdir(temp_cwd)
+        spec.loader.exec_module(module)
+        return module
+    finally:
+        os.chdir(previous_cwd)
+        if previous_anthropic is None:
+            sys.modules.pop("anthropic", None)
+        else:
+            sys.modules["anthropic"] = previous_anthropic
+        if previous_dotenv is None:
+            sys.modules.pop("dotenv", None)
+        else:
+            sys.modules["dotenv"] = previous_dotenv
+        if previous_model is None:
+            os.environ.pop("MODEL_ID", None)
+        else:
+            os.environ["MODEL_ID"] = previous_model
+        if previous_key is None:
+            os.environ.pop("ANTHROPIC_API_KEY", None)
+        else:
+            os.environ["ANTHROPIC_API_KEY"] = previous_key
+
+
+def assistant_text():
+    return {"role": "assistant", "content": [types.SimpleNamespace(type="text", text="ok")]}
+
+
+def user_text():
+    return {"role": "user", "content": "continue"}
+
+
+def tool_use_message(tool_id="tool-1"):
+    return {
+        "role": "assistant",
+        "content": [types.SimpleNamespace(type="tool_use", id=tool_id, name="bash")],
+    }
+
+
+def tool_result_message(tool_id="tool-1"):
+    return {
+        "role": "user",
+        "content": [{"type": "tool_result", "tool_use_id": tool_id, "content": "ok"}],
+    }
+
+
+def message_has_tool_use(message):
+    content = message.get("content")
+    return (
+        message.get("role") == "assistant"
+        and isinstance(content, list)
+        and any(getattr(block, "type", None) == "tool_use" for block in content)
+    )
+
+
+def assert_no_orphan_tool_results(testcase, messages):
+    for idx, message in enumerate(messages):
+        content = message.get("content")
+        if message.get("role") != "user" or not isinstance(content, list):
+            continue
+        if not any(isinstance(block, dict) and block.get("type") == "tool_result" for block in content):
+            continue
+        testcase.assertGreater(idx, 0)
+        testcase.assertTrue(message_has_tool_use(messages[idx - 1]), messages)
+
+
+class CompactionToolPairTests(unittest.TestCase):
+    def test_snip_compact_keeps_head_tool_pair(self):
+        messages = [
+            user_text(),
+            assistant_text(),
+            tool_use_message("head-tool"),
+            tool_result_message("head-tool"),
+            assistant_text(),
+            user_text(),
+            assistant_text(),
+            user_text(),
+            assistant_text(),
+            user_text(),
+        ]
+
+        for name, path in MODULES.items():
+            with self.subTest(name=name), tempfile.TemporaryDirectory() as tmp:
+                module = load_module(f"{name}_head_under_test", path, Path(tmp))
+                if name == "s09":
+                    compacted = module.snip_compact(list(messages), mx=6)
+                else:
+                    compacted = module.snip_compact(list(messages), max_messages=6)
+                self.assertEqual(compacted[2], messages[2])
+                self.assertEqual(compacted[3], messages[3])
+                assert_no_orphan_tool_results(self, compacted)
+
+    def test_snip_compact_keeps_tail_tool_pair(self):
+        messages = [
+            user_text(),
+            assistant_text(),
+            user_text(),
+            assistant_text(),
+            user_text(),
+            assistant_text(),
+            tool_use_message("tail-tool"),
+            tool_result_message("tail-tool"),
+            assistant_text(),
+            user_text(),
+        ]
+
+        for name, path in MODULES.items():
+            with self.subTest(name=name), tempfile.TemporaryDirectory() as tmp:
+                module = load_module(f"{name}_under_test", path, Path(tmp))
+                if name == "s09":
+                    compacted = module.snip_compact(list(messages), mx=6)
+                else:
+                    compacted = module.snip_compact(list(messages), max_messages=6)
+                assert_no_orphan_tool_results(self, compacted)
+
+    def test_reactive_compact_keeps_tail_tool_pair(self):
+        messages = [
+            user_text(),
+            assistant_text(),
+            user_text(),
+            tool_use_message("reactive-tool"),
+            tool_result_message("reactive-tool"),
+            assistant_text(),
+            user_text(),
+            assistant_text(),
+            user_text(),
+        ]
+
+        for name, path in MODULES.items():
+            with self.subTest(name=name), tempfile.TemporaryDirectory() as tmp:
+                module = load_module(f"{name}_reactive_under_test", path, Path(tmp))
+                module.write_transcript = lambda _messages: Path("transcript.jsonl")
+                module.summarize_history = lambda _messages: "summary"
+                compacted = module.reactive_compact(list(messages))
+                self.assertEqual(compacted[1], messages[3])
+                assert_no_orphan_tool_results(self, compacted)
+
+    def test_s20_has_tool_use_still_accepts_content_blocks(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            module = load_module("s20_has_tool_use_under_test", MODULES["s20"], Path(tmp))
+            self.assertTrue(module.has_tool_use([types.SimpleNamespace(type="tool_use")]))
+            self.assertFalse(module.has_tool_use([types.SimpleNamespace(type="text")]))
+
+
+if __name__ == "__main__":
+    unittest.main()