fix: map chat finish_reason to responses status and preserve terminal stream semantics

[jerkeyray]

Summary

Implements proper handling of incomplete responses in the OpenAI provider by mapping length finish reasons to incomplete status and preventing duplicate finish reason forwarding in streaming responses.

Changes

• Added logic to map length finish reason to incomplete status with max_output_tokens reason in both streaming and non-streaming responses
• Introduced tracking to prevent forwarding finish reasons twice when they've already been sent in streaming chunks
• Added helper functions responsesStatusFromChatFinishReason and responsesTerminalFromChatFinishReason to centralize finish reason mapping logic
• Modified streaming response handling to emit response.incomplete events instead of response.completed when appropriate
• Added comprehensive test coverage for finish reason mapping in both response formats

Type of change

• Feature
• Bug fix
• Refactor
• Documentation
• Chore/CI

Affected areas

• Core (Go)
• Transports (HTTP)
• Providers/Integrations
• Plugins
• UI (Next.js)
• Docs

How to test

Validate the finish reason mapping and incomplete response handling:

# Core/Transports
go version
go test ./...

# Test specific functionality
go test ./core/schemas -v -run TestToBifrostResponsesResponse_MapsLengthToIncomplete
go test ./core/schemas -v -run TestToBifrostResponsesStreamResponse_MapsLengthToIncompleteEvent

Test with OpenAI provider responses that hit token limits to verify incomplete status is properly set with max_output_tokens reason.

Screenshots/Recordings

N/A

Breaking changes

• Yes
• No

Related issues

Closes #1976
Closes #1821

Security considerations

No security implications - this change only affects response status mapping and metadata handling.

Checklist

• I read docs/contributing/README.md and followed the guidelines
• I added/updated tests where appropriate
• I updated documentation where needed
• I verified builds succeed (Go and UI)
• I verified the CI pipeline passes locally if applicable

[jerkeyray]

• fix: map chat finish_reason to responses status and preserve terminal stream semantics #1995 👈 (View in Graphite)
• main

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[github-actions]

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Run tests for PR #1995

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Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

core/schemas/mux.go (1)

1766-1950: ⚠️ Potential issue | 🟠 Major

length can still leave earlier text items marked as completed.

This only fixes the text item status when it is closed in the terminal chunk. If assistant text is closed earlier at the tool-call transition on Line 1597, that path still emits response.output_item.done with Status: "completed" on Line 1643. A stream that later ends with finish_reason == "length" will therefore produce response.incomplete while the already-closed text item says completed. Please defer that text output_item.done until the terminal chunk, or route the same terminal status through the earlier close path as well.

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Configuration used: Organization UI

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Run ID: 2caaf961-cc11-41a9-8400-4c6802182cfe

📥 Commits

Reviewing files that changed from the base of the PR and between 368aaf1 and 318fd68.

📒 Files selected for processing (3)

• core/providers/openai/openai.go
• core/schemas/mux.go
• core/schemas/mux_test.go