fix: pass routing info headers in error/passthrough paths

[TejasGhatte]

Summary

Error responses and passthrough responses (both streaming and non-streaming) were not emitting x-bifrost-* routing identity headers, making it impossible for callers to determine which provider ran or whether a fallback fired when a request failed or was proxied verbatim.

Changes

• Added ApplyBifrostErrorResponseHeaders in lib/responseheaders.go to bridge BifrostErrorExtraFields to the shared ApplyBifrostResponseHeaders writer, since error and success paths use different extra-fields types.
• Called ApplyBifrostErrorResponseHeaders in handlers/utils.go (SendBifrostError) and integrations/utils.go (sendStreamError) so all error responses carry routed-identity headers. Applied after provider-header forwarding so a chained upstream's x-bifrost-* headers cannot overwrite bifrost's own identity.
• Called ApplyBifrostResponseHeaders in integrations/router.go for both handlePassthroughNonStream and handlePassthroughStream, since passthrough responses forward provider bytes 1:1 and cannot carry extra_fields in the body.
• When bifrostCtx is nil (native error path), context-only headers such as x-bifrost-fallback-index and x-bifrost-upstream-latency are intentionally omitted; routing_info-* headers still report which provider ran and whether a fallback fired.
• Added TestApplyBifrostErrorResponseHeaders covering fallback-exhausted errors, the nil-context native error path, and empty extra fields.

Type of change

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

Affected areas

• Core (Go)
• Transports (HTTP)
• Providers/Integrations
• Plugins
• UI (React)
• Docs

How to test

go test ./transports/bifrost-http/lib/...
go test ./transports/bifrost-http/integrations/...
go test ./transports/bifrost-http/handlers/...

Send a request that triggers a provider error or exhausts all fallbacks and inspect the response headers — x-bifrost-provider, x-bifrost-routing-info-is-fallback, x-bifrost-routing-info-provider, and related headers should be present. Repeat with a passthrough route (streaming and non-streaming) and confirm the same identity headers appear after provider-forwarded headers.

Screenshots/Recordings

N/A

Breaking changes

• No

Related issues

N/A

Security considerations

No auth, secrets, or PII implications. Headers added are routing metadata already present on success responses.

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

[coderabbitai]

📝 Walkthrough

Walkthrough

Routed-identity headers are now applied to Bifrost error responses and streaming or non-streaming passthrough responses. A shared error-header helper maps error metadata, with tests covering fallback, native, and empty metadata cases.

Changes

Routed identity header propagation

Layer / File(s)	Summary
Error response header contract transports/bifrost-http/lib/responseheaders.go, transports/bifrost-http/lib/responseheaders_test.go	Error metadata is converted into routed-identity response headers, with coverage for fallback-exhausted, native, and empty-field responses.
Response path header wiring transports/bifrost-http/handlers/utils.go, transports/bifrost-http/integrations/utils.go, transports/bifrost-http/integrations/router.go	Error handlers and streaming/non-streaming passthrough paths apply routed-identity headers after provider headers are forwarded.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• maximhq/bifrost#5485: Modifies the shared routed-identity response-header propagation used by these paths.
• maximhq/bifrost#5495: Modifies the related routed-identity header handling in streaming HTTP response paths.

Suggested reviewers: roroghost17, akshaydeo, pratham-mishra04

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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 clearly summarizes the main change: adding routing info headers to error and passthrough paths.
Description check	✅ Passed	The description follows the required template and includes summary, changes, testing, affected areas, breaking changes, security, and checklist.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 07-24-fix_pass_routing_info_headers_in_error_passthrough_paths

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[TejasGhatte]

• fix: pass routing info headers in error/passthrough paths #5528 👈 (View in Graphite)
• fix: replicate harness test and gemini extra param #5527
• dev

This stack of pull requests is managed by Graphite. Learn more about stacking.

[coderabbitai]

Actionable comments posted: 3

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@transports/bifrost-http/integrations/router.go`:
- Line 3384: Update the response-header handling around
ApplyBifrostResponseHeaders so the streaming response always retains
Cache-Control: no-cache after passthrough headers are applied. Reassert the
no-cache directive immediately after the call, or exclude Cache-Control from the
provider headers handled there, while preserving the existing passthrough
behavior for other headers.

In `@transports/bifrost-http/integrations/utils.go`:
- Around line 169-170: Update the error-response header flow around
ApplyBifrostErrorResponseHeaders to clear the complete managed x-bifrost-*
header set after forwarding provider headers, including stale routed identity
fields, then apply bifrostErr.ExtraFields so route-derived values overwrite
forwarded headers. Preserve the existing provider-header forwarding and
route-derived header behavior.
- Around line 169-170: Reserve the managed x-bifrost-* namespace after
provider-header forwarding and before applying routed identity fields. In
transports/bifrost-http/integrations/utils.go lines 169-170, clear every managed
Bifrost identity header before ApplyBifrostErrorResponseHeaders; apply the same
clearing in transports/bifrost-http/integrations/router.go lines 3287-3290 and
3381-3384 for non-stream and stream passthrough paths, respectively. Add a
regression test covering upstream Bifrost identity collisions.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: cf881b5b-10e7-4200-a4a5-3a64b0853dda

📥 Commits

Reviewing files that changed from the base of the PR and between 820518a and 1a21bc9.

📒 Files selected for processing (5)

• transports/bifrost-http/handlers/utils.go
• transports/bifrost-http/integrations/router.go
• transports/bifrost-http/integrations/utils.go
• transports/bifrost-http/lib/responseheaders.go
• transports/bifrost-http/lib/responseheaders_test.go

[akshaydeo]

Merge activity

• Jul 24, 12:46 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Jul 24, 12:48 PM UTC: @akshaydeo merged this pull request with Graphite.

The base branch was changed.