Fix runTools readable stream round trip tool results

[momomuchu]

Summary

When a streaming runTools() run is serialized with toReadableStream() and reconstructed with fromReadableStream(), tool result messages were lost. The proxied runner kept assistant messages rebuilt from chunks, but missed { role: 'tool' } messages and the related functionToolCallResult event.

Root cause

The readable stream protocol only wrote raw ChatCompletionChunk lines. Local tool result messages are added by the runner after tool execution, so they were never present in the serialized stream.

Fix

ChatCompletionStreamingRunner.toReadableStream() now keeps normal chunk lines unchanged and adds tool result messages as a small envelope line shaped { type: 'message', message }. fromReadableStream() consumes that envelope as a real message and uses it as a completion boundary. The stream end guard now accepts a stream that ends after a tool message while preserving request ended without sending any chunks for truly empty streams.

Compatibility

Old raw chunk streams still reconstruct the same way. ChatCompletionChunk has no top level type field, so an old chunk is not mistaken for a message envelope. Assistant messages are still rebuilt from chunks, so this does not duplicate assistant messages.

Scope

The PR template warns that this SDK is generated. This change is confined to src/lib, which is hand written and not generator owned. Tests are confined to tests/lib.

Tests

./scripts/test tests/lib tests/api-resources

682 passed. No failures.

Fixes #1060

[chatgpt-codex-connector]

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[HAYDEN-OAI]

pushed a follow-up in 91feb7d7 that preserves normalized tool-call ids across the readable-stream relay and encodes tool-result records as legacy-safe empty chunks, so older fromReadableStream() consumers do not crash. i also added regressions for empty-id round trips and legacy chunk readers.

verified with pnpm exec jest tests/lib/ChatCompletionRunFunctions.test.ts --runInBand --verbose --no-cache, pnpm exec tsc --noEmit, and pnpm build.