Preserve snapshots when resuming response streams

[koriyoshi2041]

Problem

responses.stream({ response_id, starting_after }) needs the replayed event prefix to build complete event snapshots and finalResponse(). Passing starting_after through to responses.retrieve makes the API omit that prefix, including response.created, so the accumulator can fail before yielding resumed events.

Fix

• Keep the full replay for the by-ID stream helper and continue filtering emitted events locally.
• Clarify the starting_after docs so the snapshot-building behavior is explicit.
• Add a regression test that emulates the API's truncated suffix behavior and verifies resumed streams still build a final response.

Test

• pnpm test tests/lib/ResponseStream.test.ts
• pnpm lint

Related to #1983.

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[HAYDEN-OAI]

updated this in 9fe6084b. we kept the full replay for responses.stream({ response_id, starting_after }) so the accumulator still sees response.created, clarified that starting_after filters emitted events locally, and replaced the url-only test with a regression test that simulates a server-truncated suffix and verifies finalResponse() still succeeds. verified with pnpm test tests/lib/ResponseStream.test.ts and pnpm lint.

[koriyoshi2041]

Thanks, this version looks right to me. I pulled 9fe6084b locally and re-ran:

• pnpm test tests/lib/ResponseStream.test.ts
• pnpm lint

Both pass. The new regression is a better fit than my original URL-only test since it checks the truncated replay case directly.