fix(ai-gateway): close terminal SSE streams

[chrarnoldus]

Summary

• close Responses API streams after forwarding response.completed, response.incomplete, or response.failed
• close Anthropic Messages streams after forwarding message_stop
• normalize and forward [DONE] before immediately closing compatible Messages, Chat Completions, and Responses streams
• cancel upstream readers, preserve raw stream capture, and discard events after protocol terminal markers
• cover never-ending upstream streams for each terminal behavior

Testing

• Not run locally per request; CI will validate the change.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

Incremental review of the terminal-marker handling extended to Chat Completions ([DONE]) and Anthropic Messages (message_stop/[DONE]) found no defects: post-terminal events and comments are correctly suppressed, the normalized [DONE] sentinel is emitted exactly once (the terminal branch returns before the EOF branch can re-emit it), and raw-body capture plus upstream cancellation match the new tests.

Files Reviewed (2 files)

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

Previous Review Summary (commit c85923a)

Current summary above is authoritative. Previous snapshots are kept for context only.

Previous review (commit c85923a)

Status: No Issues Found | Recommendation: Merge

Executive Summary

The change correctly detects terminal Responses API SSE events (response.completed/incomplete/failed), forwards them, cancels the upstream reader, and closes the downstream stream without waiting for EOF; the added tests cover forwarding, cancellation, and raw-body capture consistently with the implementation.

Files Reviewed (2 files)

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

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