refactor: extract stream errors to open-sse/utils/stream/errors.ts (Issue #3594)

[oyi77]

Part of modularization effort (Issue #3594).

Extracts error handling from the monolithic open-sse/utils/stream.ts into a dedicated module.

Changes:

• New file: open-sse/utils/stream/errors.ts (87 lines)
• Exports: toStreamFailureStatus, looksLikeStreamRateLimit, normalizeStreamFailurePayload

Testing: No behavior change. Existing stream tests pass.

Follow-up PRs will extract: types (#3917), utils (#3918), textualToolCalls, sseFormatters, openaiChunks, claudeLifecycle, responsesLifecycle, and streamCore.

[gemini-code-assist]

Code Review

This pull request introduces a new utility file open-sse/utils/stream/errors.ts to normalize and handle upstream stream failure payloads. The feedback highlights two main issues: unused imports (convertOpenAIToResponsesToolCall and uuidv4) that should be removed, and a violation of the repository style guide requiring unit tests to be added for any new production code under open-sse/.

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[gemini-code-assist]

The imports convertOpenAIToResponsesToolCall and uuidv4 are not used anywhere in this file. They should be removed to keep the codebase clean and avoid unnecessary dependencies.

Suggested change

	import { convertOpenAIToResponsesToolCall } from "../handlers/responseTranslator.ts";
	import { v4 as uuidv4 } from "uuid";
	import { asRecord } from "./utils.ts";
	import { JsonRecord, StreamFailurePayload } from "./types.ts";
	import { asRecord } from "./utils.ts";
	import { JsonRecord, StreamFailurePayload } from "./types.ts";

[gemini-code-assist]

According to the Repository Style Guide (Rule 9), we must always include tests when changing or adding production code under open-sse/. Please add unit tests for these extracted stream error utility functions (e.g., toStreamFailureStatus, looksLikeStreamRateLimit, and normalizeStreamFailurePayload) inside the tests/unit/ directory.

References

1. Always include tests when changing production code (src/, open-sse/, electron/, bin/). ^(link)

[diegosouzapw]

Thanks, @oyi77 🙏. These stream extractions are currently additive — the new modules under open-sse/utils/stream/ aren't wired into stream.ts yet, so they don't change runtime behavior on their own. Rather than land the decomposition in fragments, we're going to fold the stream split into the single coordinated modularization pass (Issue #3594) after the quality-gate work lands, so the extraction and the rewiring get sequenced together and verified lossless in one go. Closing for now — purely sequencing, not a reflection on the work; input welcome on #3594 once the plan is up.