[Kayvan-Zahiri]

Problem

Both assistant chat endpoints parse each SSE data: line as a complete JSON object. A valid event with JSON spread across multiple data fields raises orjson.JSONDecodeError in both synchronous and asynchronous clients. This was reproduced with replayed HTTP responses, not observed against a hosted assistant.

Solution

Share a small event-data assembler across the four parsers. Join data fields with newlines and decode only after an event boundary, ignoring non-data fields and comments. Preserve the existing final-event-at-EOF compatibility and [DONE] handling. Completed events are yielded immediately without reading the next event.

The event framing follows the SSE interpretation rules; the existing EOF compatibility is intentionally retained.

Type of Change

• Bug fix (non-breaking change which fixes an issue)

Test Plan

• Four public-client regressions fail before the fix (both endpoints × sync/async).
• 604 focused chat conformance, assistant-model, streaming parity, and SSE tests pass after the fix.
• Coverage includes multiple events, comments and other fields, empty data, single-space handling, EOF, and incremental delivery.
• Ruff lint/format checks and Mypy on all three changed source modules pass.
• A broader unit run was interrupted: native gRPC tests require the unbuilt Rust extension, and interruption affected a retry-storm test. It is not claimed as passing. No hosted API requests were made.