Consolidate Odysseus agent harness and tool contracts

tests/test_filesystem_tool_argument_validation.py

@@ -39,3 +39,54 @@ async def test_filesystem_tools_reject_invalid_structured_arguments_before_disk_
     assert result["exit_code"] == 1
     assert error_fragment in result["error"]
     assert resolved == []
+
+
+@pytest.mark.asyncio
+async def test_write_file_preserves_existing_binary_artifact(tmp_path, monkeypatch):
+    import src.tool_execution as tool_execution
+
+    target = tmp_path / "output.pdf"
+    original = b"%PDF-1.7\nvalid binary payload\x00\xff"
+    target.write_bytes(original)
+    monkeypatch.setattr(tool_execution, "_resolve_tool_path", lambda _path: str(target))
+
+    result = await WriteFileTool().execute(
+        '{"path":"output.pdf","content":"The PDF is already complete."}', {}
+    )
+
+    assert result["exit_code"] == 1
+    assert result["binary_artifact_preserved"] is True
+    assert "binary artifact path" in result["error"]
+    assert target.read_bytes() == original
+
+
+@pytest.mark.asyncio
+async def test_write_file_rejects_new_binary_artifact_path(tmp_path, monkeypatch):
+    import src.tool_execution as tool_execution
+
+    target = tmp_path / "new.pdf"
+    monkeypatch.setattr(tool_execution, "_resolve_tool_path", lambda _path: str(target))
+
+    result = await WriteFileTool().execute(
+        '{"path":"new.pdf","content":"not really a PDF"}', {}
+    )
+
+    assert result["exit_code"] == 1
+    assert result["binary_artifact_preserved"] is False
+    assert not target.exists()
+
+
+@pytest.mark.asyncio
+async def test_write_file_still_rewrites_existing_text_file(tmp_path, monkeypatch):
+    import src.tool_execution as tool_execution
+
+    target = tmp_path / "notes.txt"
+    target.write_text("old", encoding="utf-8")
+    monkeypatch.setattr(tool_execution, "_resolve_tool_path", lambda _path: str(target))
+
+    result = await WriteFileTool().execute(
+        '{"path":"notes.txt","content":"new"}', {}
+    )
+
+    assert result["exit_code"] == 0
+    assert target.read_text(encoding="utf-8") == "new"