fix: dropped instructions and content_filter status on responses->chat fallback

[Shaik-Sirajuddin]

Summary

Every provider without native Responses API support (Ollama, vLLM, DeepSeek, Groq, Mistral, and others) converts v1/responses requests to Chat Completions via ToChatRequest. That conversion silently discarded the caller's instructions field and never mapped a content_filter finish reason to an incomplete status — responses came back well-formed but semantically wrong, with no signal anything was lost.

Changes

• Prepend instructions as a leading system message in ToChatRequest (mirrors LiteLLM's equivalent chat-completions bridge).
• Map content_filter finish reason to status: incomplete, reusing the previously-declared-but-unused ResponsesResponseIncompleteReasonContentFilter constant — fixes both streaming and non-streaming paths since they share one mapping function.
• Log a warning whenever a tool or tool_choice value is dropped for having no Chat Completions equivalent, via a new FallbackWarningHook (thread-safe atomic.Pointer, following the existing providerUtils.SetLogger/getLogger convention).

Type of change

• Bug fix

How to test

cd core
go test ./schemas/... -run "TestToChatRequest|TestToBifrostResponses"
go test -race ./schemas/...

Also verified live end-to-end against a real Ollama backend (qwen3:0.6b) via the openai Python SDK — before/after request/response transcripts, server logs, and terminal screenshots are in memory/gen/responses-chat-fallback/reports/.

Breaking changes

• No

[CLAassistant]

All committers have signed the CLA.

[coderabbitai]

📝 Walkthrough

Walkthrough

Responses-to-Chat fallback conversion now preserves instructions, logs dropped unsupported fields, and receives provider loggers across fallback paths. Finish-reason mapping and tests now cover content-filter incomplete responses and streams.

Changes

Responses fallback behavior

Layer / File(s)	Summary
Fallback conversion and warning hooks core/schemas/mux.go, core/schemas/mux_test.go	ToChatRequest preserves instructions as a leading system message, logs dropped tools and tool choices, and retains compatibility with existing conversion tests.
Provider fallback logger propagation core/providers/*	Responses and ResponsesStream fallback paths pass provider loggers into ToChatRequest; the Hugging Face adapter forwards optional logger arguments.
Finish-reason mapping coverage core/schemas/mux.go, core/schemas/mux_test.go	Max-output-tokens uses the defined constant, while content-filter results map to incomplete non-streaming responses and terminal streaming events.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant ResponsesProvider
  participant ToChatRequest
  participant Logger
  participant ChatCompletion
  Client->>ResponsesProvider: submit Responses request
  ResponsesProvider->>ToChatRequest: convert with provider logger
  ToChatRequest->>Logger: warn about dropped unsupported fields
  ToChatRequest-->>ChatCompletion: return Chat request
  ChatCompletion-->>ResponsesProvider: return response or stream
  ResponsesProvider-->>Client: return Responses result

Loading

Possibly related PRs

• maximhq/bifrost#3505: Both modify the Responses-to-Chat fallback path and converted request handling.
• maximhq/bifrost#4813: Both modify Perplexity Responses fallback routing.

Suggested reviewers: akshaydeo, pratham-mishra04

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 12.50% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title matches the main change: fixing dropped instructions and content_filter handling in responses→chat fallback.
Description check	✅ Passed	The description covers summary, changes, type of change, testing, and breaking changes, though several optional template sections are omitted.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[greptile-apps]

Confidence Score: 5/5

This looks safe to merge.

• The instance logger is passed through all changed unary and streaming fallback paths.
• The previous cross-instance warning attribution problem is no longer reachable.
• No blocking issues were found in the updated code.

Important Files Changed

Filename	Overview
core/schemas/mux.go	Preserves instructions, maps filtered responses to incomplete status, and emits fallback warnings through a caller-supplied logger.
core/providers/huggingface/responses.go	Forwards the optional logger while preserving the existing exported call shape.
core/providers/openai/openai.go	Passes the provider instance logger through unary and streaming fallback conversions.
core/schemas/mux_test.go	Adds coverage for instruction preservation and content-filter status mapping.

_{Reviews (3): Last reviewed commit: "fix: dropped instructions and content_fi..." | Re-trigger Greptile}

[Shaik-Sirajuddin]

Before/after evidence for the Greptile P1 fix

Addressing the review comment with logs, not just a claim.

Before (commit 973fc3a2c) — the bug

$ grep -n "FallbackWarningHook\|fallbackWarningHook" core/schemas/mux.go core/bifrost.go
schemas/mux.go:1288:var fallbackWarningHook atomic.Pointer[func(msg string, args ...any)]
schemas/mux.go:1291:func SetFallbackWarningHook(hook func(msg string, args ...any)) {
core/bifrost.go:226:	schemas.SetFallbackWarningHook(config.Logger.Warn)

A single package-level atomic.Pointer set on every Init() call — the second Bifrost instance's Init() silently overwrites the first instance's routing, exactly as described in the review comment.

After (commit 4ae75d493) — fixed

$ grep -n "FallbackWarningHook\|fallbackWarningHook" core/schemas/mux.go core/bifrost.go
(no matches)

$ grep -rn "ToChatRequest(provider.logger)\|ToChatRequest(p.logger)" core/providers | wc -l
26

The global hook is gone. All 26 call sites across the 15 chat-fallback providers now pass that provider's own logger field (bound at construction time, one per Bifrost instance) directly into ToChatRequest(logger ...Logger) — variadic so the exported zero-argument call shape still compiles for existing Go SDK consumers.

Build/vet/test — both commits

go build ./...   # clean, both commits
go vet ./...     # clean, both commits
go test ./schemas/... ./providers/...
  # both commits: all packages pass except the same pre-existing
  # TestToOpenAIResponsesRequest_GPTOSS_SummaryToContentBlocks failure,
  # confirmed unrelated to this change (reproduces on a clean checkout
  # with none of this branch's changes applied).

Full logs (build/vet/test output + the exact grep runs above) captured for both commits — happy to paste in full if useful, trimmed here for readability.