fix(ai-gateway): clarify interrupted stream errors

[chrarnoldus]

Summary

• clarify that a mid-stream ResponseAborted can indicate either a provider disconnect or a request timeout
• preserve the existing upstream_disconnect error type and distinct TimeoutError handling
• update exact JSON and SSE message assertions with and without a Vercel request id

Why

The previous message said the provider disconnected, but ResponseAborted only establishes that the response stream was interrupted. A timeout at the provider, intermediary, or request layer can surface through the same read-error path, so the injected client message should not claim a single cause.

Verification

• pnpm --filter web exec jest --runInBand --forceExit src/lib/rewriteModelResponse.test.ts (72 tests passed)
• pnpm exec oxfmt --list-different apps/web/src/lib/rewriteModelResponse.ts apps/web/src/lib/rewriteModelResponse.test.ts
• git diff --check

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

Message-only change to the ResponseAborted read-error text in the AI gateway response rewriter, with matching exact-string test updates; the upstream_disconnect error type, 503 status, request-id suffix behavior, and the separate TimeoutError path are all unchanged, so behavioral risk is minimal (high confidence).

Files Reviewed (2 files)

• apps/web/src/lib/rewriteModelResponse.ts
• apps/web/src/lib/rewriteModelResponse.test.ts

Verification Notes

• Checked for other consumers of the old string (The upstream provider disconnected while sending the response.): no remaining references in the repo.
• Confirmed apps/web/src/tests/openrouterApi.timeout.test.ts asserts different messages produced by upstream-request.ts and is unaffected.
• Read-only mode: no tests were executed in this session; test results reported in the PR description were not independently reproduced.

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_{Reviewed by claude-opus-5 · Input: 20 · Output: 3.4K · Cached: 430.5K}

_{Review guidance: REVIEW.md from base branch main}