feat: Add pathlib.Path normalization to string representation

src/toon_format/normalize.py

@@ -6,6 +6,7 @@
 - datetime/date → ISO 8601 strings
 - Decimal → float
 - tuple/set/frozenset → sorted lists
+- pathlib.Path → string representation
 - Infinity/NaN → null
 - Functions/callables → null
 - Negative zero → zero
@@ -16,6 +17,7 @@
 from collections.abc import Mapping
 from datetime import date, datetime
 from decimal import Decimal
+from pathlib import PurePath
 from typing import Any
 
 # TypeGuard was added in Python 3.10, use typing_extensions for older versions
@@ -39,6 +41,7 @@ def normalize_value(value: Any) -> JsonValue:
     Converts Python-specific types to JSON-compatible equivalents:
     - datetime objects → ISO 8601 strings
     - sets → sorted lists
+    - pathlib.Path → string representation
     - Large integers (>2^53-1) → strings (for JS compatibility)
     - Non-finite floats (inf, -inf, NaN) → null
     - Negative zero → positive zero
@@ -64,10 +67,15 @@ def normalize_value(value: Any) -> JsonValue:
         >>> normalize_value(2**60)  # Large integer
         '1152921504606846976'
 
+        >>> from pathlib import Path
+        >>> normalize_value(Path('/tmp/file.txt'))
+        '/tmp/file.txt'
+
     Note:
         - Recursive: normalizes nested structures
         - Sets are sorted for deterministic output
         - Heterogeneous sets sorted by repr() if natural sorting fails
+        - Path objects are converted to their string representation
     """
     if value is None:
         return None
@@ -100,6 +108,11 @@ def normalize_value(value: Any) -> JsonValue:
             return None
         return float(value)
 
+    # Handle pathlib.Path objects -> string representation
+    if isinstance(value, PurePath):
+        logger.debug(f"Converting {type(value).__name__} to string: {value}")
+        return str(value)
+
     if isinstance(value, datetime):
         try:
             result = value.isoformat()

tests/test_normalization.py

@@ -17,6 +17,7 @@
 """
 
 from decimal import Decimal
+from pathlib import Path, PurePosixPath, PureWindowsPath
 
 from toon_format import decode, encode
 
@@ -416,3 +417,66 @@ def test_roundtrip_numeric_precision(self):
         # All numbers should round-trip with fidelity
         for key, value in original.items():
             assert decoded[key] == value, f"Mismatch for {key}: {decoded[key]} != {value}"
+
+
+class TestPathNormalization:
+    """Test pathlib.Path normalization to strings."""
+
+    def test_path_to_string(self):
+        """pathlib.Path should be converted to string."""
+        data = {"file": Path("/tmp/test.txt")}
+        result = encode(data)
+        decoded = decode(result)
+
+        assert decoded["file"] == "/tmp/test.txt"
+
+    def test_relative_path(self):
+        """Relative paths should be preserved."""
+        data = {"rel": Path("./relative/path.txt")}
+        result = encode(data)
+        decoded = decode(result)
+
+        # Path normalization may vary, but should be a string
+        assert isinstance(decoded["rel"], str)
+        assert "relative" in decoded["rel"]
+        assert "path.txt" in decoded["rel"]
+
+    def test_pure_path(self):
+        """PurePath objects should also be normalized."""
+        data = {
+            "posix": PurePosixPath("/usr/bin/python"),
+            "windows": PureWindowsPath("C:\\Windows\\System32"),
+        }
+        result = encode(data)
+        decoded = decode(result)
+
+        assert decoded["posix"] == "/usr/bin/python"
+        assert decoded["windows"] == "C:\\Windows\\System32"
+
+    def test_path_in_array(self):
+        """Path objects in arrays should be normalized."""
+        data = {"paths": [Path("/tmp/a"), Path("/tmp/b"), Path("/tmp/c")]}
+        result = encode(data)
+        decoded = decode(result)
+
+        assert decoded["paths"] == ["/tmp/a", "/tmp/b", "/tmp/c"]
+
+    def test_path_in_nested_structure(self):
+        """Path objects in nested structures should be normalized."""
+        data = {
+            "project": {
+                "root": Path("/home/user/project"),
+                "src": Path("/home/user/project/src"),
+                "files": [
+                    {"name": "main.py", "path": Path("/home/user/project/src/main.py")},
+                    {"name": "test.py", "path": Path("/home/user/project/src/test.py")},
+                ],
+            }
+        }
+        result = encode(data)
+        decoded = decode(result)
+
+        assert decoded["project"]["root"] == "/home/user/project"
+        assert decoded["project"]["src"] == "/home/user/project/src"
+        assert decoded["project"]["files"][0]["path"] == "/home/user/project/src/main.py"
+        assert decoded["project"]["files"][1]["path"] == "/home/user/project/src/test.py"