[RaphaelFakhri]

Description

JSON request bodies and JSON key-value store records were serialized with json.dumps(..., default=str). A datetime was sent as 2026-01-01 00:00:00+00:00 instead of ISO 8601, and a set or any custom object was stored as its str() representation without an error.

This change adds one shared default hook, json_default in _utils/http.py, and uses it in both encoders:

• datetime, date and time are encoded with isoformat().
• UUID is encoded with str().
• Pydantic URLs are encoded as strings. Request models dumped in Python mode keep AnyUrl objects, for example request_url in WebhookClient.update(), which previously relied on str().
• Any other type raises TypeError with the type name. For set_record(), the message also suggests passing bytes or a string with a matching content type.
• allow_nan=False is unchanged.
• Request queue batches are unchanged. Request models are dumped with model_dump(mode='json', fallback=str) first, so an unsupported value in userData is still sent as its str().

The hook lives in _utils/http.py because _utils/encoding.py imports http_clients, so importing it from http_clients/_base.py would create a circular import.

Issues

• Closes JSON request bodies serialize unknown types with str(), including datetime #1172

Testing

• New unit tests:
  • test_prepare_request_call_encodes_datetime_as_iso_8601
  • test_prepare_request_call_encodes_time_and_uuid_as_strings
  • test_prepare_request_call_rejects_non_json_value (set, object)
  • test_encode_key_value_store_record_value_encodes_datetime_as_iso_8601
  • test_encode_key_value_store_record_value_rejects_non_json_value
  • test_update_sends_request_url_as_string: guards the webhook URL path.
• Without the source change, 5 of the new tests fail. With it, all 8 pass. The full unit suite passes (2573 tests).
• ruff check, ruff format --check, ty check, and poe check-docstrings pass.

[vdusek]

Issue #1172 is in the 4.0 milestone because this change is breaking: calls that work on 3.4.0 would raise TypeError after it, for example a set, Decimal, or custom object in run input or push_items. We can't ship it in 3.x, so I'm closing this PR.

✍️ Drafted by Claude Code