[Kayvan-Zahiri]

The sync and async LLM Gateway stream readers require the literal prefix data: . SSE permits the space after the colon to be omitted, so valid data:{...} frames are silently skipped. An unspaced data:[DONE] is also ignored, allowing later frames to be emitted instead of ending the iterator.

Accept the data: field prefix and retain the existing payload trimming. Ignore empty data payloads so previously ignored unspaced keepalive frames do not become JSON parse errors. Response parsing, setup-error handling, and the existing spaced format remain unchanged. This is a narrow single-line framing fix, not a full SSE parser rewrite.

Added eight public sync/async Gateway tests covering the Cartesian product of spaced/unspaced chunk and [DONE] fields, empty keepalive data, comments, unrelated fields, CRLF framing, a distinct post-sentinel chunk that must not be yielded, and response closure. Six cases fail against the original code; two are controls.

The optional space is specified by the SSE parsing algorithm. Reproduction uses controlled HTTP responses; it does not establish that the hosted gateway currently emits unspaced frames. No live inference calls were made.

Validation:

• Final full suite: 749 passed (189 warnings). Local TLS tests require loopback access; the first sandboxed run had five bind-permission failures, and all passed with local socket access.
• Separately, all 43 LLM Gateway tests pass with Pydantic 1, including the new cases.
• Changed-file Ruff lint/format and git diff --check pass.
• Full repository Ruff has 12 existing findings; restoring the original source reproduces the same findings.
• Wheel and source distribution build successfully.