fix: settle async streams on executor rejection

[sylvesterkaczmarek]

Summary

Prevent AsyncStreamResponse from hanging when a subscriber-provided executor rejects the delivery task.

CompletableFuture.whenCompleteAsync(..., executor) reports executor dispatch failures through its dependent future. The current subscription path discards that future, so a rejected task can leave onCompleteFuture() pending indefinitely and the underlying response unclosed.

Fixes #973.

Changes

• wrap the subscriber executor so dispatch failures settle onCompleteFuture() exceptionally;
• close the asynchronous stream when that failure wins terminal settlement;
• rethrow the executor failure so the dependent CompletableFuture retains normal exceptional-completion semantics;
• keep handler delivery on the requested executor only, with no fallback execution on another thread;
• add a deterministic regression using a rejecting executor.

Testing

• pre-fix regression reproduced on current main: onCompleteFuture().get(100ms) timed out
• ./gradlew :openai-java-core:test --tests com.openai.core.http.AsyncStreamResponseTest --no-daemon --console=plain — passed
• ./gradlew :openai-java-core:lintKotlin --no-daemon --console=plain — passed
• git diff --check — passed
• Castiron custom-code budget check — passed, 1906 / 2000 lines with 94 lines headroom

Risk and rollout

Low. Successful executor dispatch and existing stream completion behavior are unchanged. The new path runs only when the supplied executor throws while accepting the delivery task. Older and normal executors retain the existing behavior.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-04T11:25:21.555627Z	7c77d21	PR opened
🔒 Security Review	✅ Completed 2026-09-04T11:25:26.037170Z	7c77d21	PR opened

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