fix(python): preserve original JSON keys in Data shim round-trips (#1900)

* fix(python): preserve original JSON keys in Data shim round-trips

Fixes #1138

The Data compatibility shim converted JSON keys to snake_case for attribute
access but could not reconstruct abbreviation-heavy camelCase keys (userURL,
sessionID, OAuthToken) on to_dict(). Store the original JSON key per field
during from_dict() and prefer it when serializing back.

Includes regression tests for the abbreviation key cases described in the
issue.

* fix(python): preserve colliding Data JSON keys

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: syf2211 <syf2211@users.noreply.github.com>
Co-authored-by: Shay Rojansky <roji@roji.org>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: 3 people

python/copilot/generated/session_events.py

@@ -138,6 +138,22 @@ def test_data_shim_preserves_raw_mapping_values(self):
         constructed = Data(arguments={"tool_call_id": "call-1"})
         assert constructed.to_dict() == {"arguments": {"tool_call_id": "call-1"}}
 
+    def test_data_shim_preserves_abbreviation_json_keys_on_round_trip(self):
+        """Data.from_dict(x).to_dict() should preserve JSON keys with abbreviations.
+
+        Regression test for github/copilot-sdk#1138: keys like userURL, sessionID,
+        and OAuthToken were rewritten on round-trip because _compat_to_json_key could
+        not reconstruct the original camelCase abbreviation casing.
+        """
+        for key in ["userURL", "sessionID", "XMLPayload", "serverIP", "OAuthToken"]:
+            incoming = {key: 42}
+            assert Data.from_dict(incoming).to_dict() == incoming
+
+    def test_data_shim_preserves_colliding_json_keys_on_round_trip(self):
+        """Data.from_dict(x).to_dict() should preserve keys with the same Python name."""
+        colliding_keys = {"userURL": 42, "userUrl": 43}
+        assert Data.from_dict(colliding_keys).to_dict() == colliding_keys
+
     def test_missing_optional_fields_remain_none_after_parsing(self):
         """Generated event models should leave missing optional fields as None.
 

python/test_event_forward_compatibility.py

@@ -2673,19 +2673,34 @@ export function generatePythonSessionEventsCode(schema: JSONSchema7): string {
     out.push(``);
     out.push(`    def __init__(self, **kwargs: Any):`);
     out.push(`        self._values = {key: _compat_from_json_value(value) for key, value in kwargs.items()}`);
+    out.push(`        self._json_keys: dict[str, str] = {}`);
+    out.push(`        self._json_values: dict[str, Any] | None = None`);
     out.push(`        for key, value in self._values.items():`);
     out.push(`            setattr(self, key, value)`);
     out.push(``);
     out.push(`    @staticmethod`);
     out.push(`    def from_dict(obj: Any) -> "Data":`);
     out.push(`        assert isinstance(obj, dict)`);
-    out.push(
-        `        return Data(**{_compat_to_python_key(key): _compat_from_json_value(value) for key, value in obj.items()})`
-    );
+    out.push(`        data = Data()`);
+    out.push(`        data._values = {}`);
+    out.push(`        data._json_keys = {}`);
+    out.push(`        data._json_values = {}`);
+    out.push(`        for key, value in obj.items():`);
+    out.push(`            py_key = _compat_to_python_key(key)`);
+    out.push(`            json_value = _compat_from_json_value(value)`);
+    out.push(`            data._values[py_key] = json_value`);
+    out.push(`            data._json_keys[py_key] = key`);
+    out.push(`            data._json_values[key] = json_value`);
+    out.push(`            setattr(data, py_key, data._values[py_key])`);
+    out.push(`        return data`);
     out.push(``);
     out.push(`    def to_dict(self) -> dict:`);
+    out.push(`        if self._json_values is not None:`);
+    out.push(
+        `            return {key: _compat_to_json_value(value) for key, value in self._json_values.items() if value is not None}`
+    );
     out.push(
-        `        return {_compat_to_json_key(key): _compat_to_json_value(value) for key, value in self._values.items() if value is not None}`
+        `        return {(self._json_keys.get(key) or _compat_to_json_key(key)): _compat_to_json_value(value) for key, value in self._values.items() if value is not None}`
     );
     out.push(``);
     out.push(``);