fix: complete visible thinking items on the streaming Responses surface

[fus3r]

Summary

Fixes #5149.

On streamed /v1/responses from Anthropic-family backends with extended thinking enabled, visible thinking blocks stream their deltas but are never completed: reasoning_summary_text.done carries an empty text, output_item.done for the reasoning index degrades to an empty "message" shell that contradicts its own output_item.added, and response.completed omits the reasoning item (and the signature) entirely. Clients that treat response.completed as the authoritative final snapshot (the openai-python streaming helper does, and so does the openai-node version Bifrost's integrations pin) lose the reasoning block, and a tool loop that echoes the output back silently drops the model's thinking from its own conversation history.

The cause is that the completion side of the visible-thinking lifecycle was never implemented: the thinking start case doesn't persist its item into state.OutputItems (every other item type does), thinking deltas aren't buffered anywhere, and state.ReasoningSignatures has been write-only since #895. #5094 fixed the same gap for redacted_thinking only.

Changes

• core/providers/anthropic/responses.go
  • add ReasoningTextBuffers to the stream state (mirror of TextBuffers), covered in the pool New/acquire/flush resets
  • persist the reasoning item into state.OutputItems at content_block_start, mirroring the redacted_thinking case
  • buffer thinking_delta text per output index (with a defensive lazy map init, same pattern as the input-JSON buffers)
  • at content_block_stop, fold the accumulated text and the stored signature into the item using the exact shape the non-streaming converter produces (reasoning_text content block with text + signature), emit reasoning_summary_text.done with the full text and content_part.done with the completed part (mirroring the text-block path); the generic done path then emits a correct output_item.done and response.completed carries the item
• core/providers/anthropic/visiblethinkingresponses_test.go: four behavior tests covering full lifecycle completion, JSON round-trip replay of the streamed done item through ToAnthropicResponsesRequest (thinking with signature must precede tool_use), interleaved multi-block isolation, and signature-less thinking
• core/changelog.md: changelog entry

All four tests fail on current dev with the exact reported symptoms and pass with the fix. The redacted_thinking suite, the passthrough suite, and the full anthropic package are green; go vet clean; golangci-lint findings identical before/after.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Affected areas

• Core (Go)
• Providers / Integrations

How to test

cd core
go test ./providers/anthropic/ -run "VisibleThinking" -count=1 -v

To see the wire difference live, stream a Responses request with reasoning enabled and a tool against an Anthropic key and inspect reasoning_summary_text.done, the reasoning output_item.done, and response.completed before and after this change; then echo response.completed.output back with a function_call_output as the next turn: before the fix the echoed history carries no reasoning item, after it the thinking block and its signature are preserved.

Breaking changes

None. Additive on the streaming completion path; the added/delta events are unchanged, and the completed item uses the same shape the non-streaming converter already produces (which the request converter already replays).

Related issues

Fixes #5149. Sibling of #5094, which covered the redacted_thinking variant of the same lifecycle gap.

Security considerations

None. No new inputs are parsed; the change only carries already-received stream content into the completion events.

Checklist

• I have performed a self-review of my code
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Any dependent changes have been merged and published

[greptile-apps]

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
core/providers/anthropic/responses.go	Adds buffering and completion logic so streamed visible thinking is included in done events and final Responses output.
core/providers/anthropic/visiblethinkingresponses_test.go	Adds tests for visible thinking completion, replay, interleaved blocks, and signature-less thinking.
core/changelog.md	Adds a changelog note for the visible thinking streaming fix.

_{Reviews (3): Last reviewed commit: "Merge branch 'dev' into fix-responses-st..." | Re-trigger Greptile}

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

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Review profile: CHILL

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Run ID: 835560a5-beb5-4f77-82cf-96b09eef7f22

📥 Commits

Reviewing files that changed from the base of the PR and between ef380f9 and 802ea6b.

📒 Files selected for processing (1)

• core/providers/anthropic/responses.go

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📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Fixed streaming “visible thinking” so completed/done fields now include the full accumulated reasoning text and any signature (when present).
  • Ensured reasoning is folded into completion events with the correct structure and ordering, including across interleaved thinking blocks and tool calls.
• Tests
  • Added integration-style coverage for visible-thinking streaming completion, replaying into requests, multiple blocks, and signature vs. no-signature behavior.

Walkthrough

Anthropic Responses streaming now buffers visible-thinking text per output index, preserves signatures, completes reasoning output items, includes them in response.completed, and supports replay into subsequent Anthropic requests. Regression tests cover ordering, interleaving, replay, and unsigned reasoning.

Changes

Visible-thinking streaming

Layer / File(s)	Summary
Reasoning stream state lifecycle core/providers/anthropic/responses.go	Adds per-output-index reasoning buffers and integrates them into stream-state initialization, reset, and cleanup.
Reasoning completion flow core/providers/anthropic/responses.go	Persists thinking items, accumulates deltas, folds text and signatures into completed reasoning content, and emits completed reasoning events and output.
Visible-thinking replay and regression coverage core/providers/anthropic/visiblethinkingresponses_test.go, core/changelog.md	Tests completion events, output ordering, request replay, multiple thinking blocks, missing signatures, and documents the fix.

Estimated code review effort: 4 (Complex) | ~45 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Anthropic as Anthropic SSE
  participant Converter as ToBifrostResponsesStream
  participant State as AnthropicResponsesStreamState
  participant Client as Responses client
  Anthropic->>Converter: thinking block start and text deltas
  Converter->>State: persist item and buffer reasoning text
  Anthropic->>Converter: thinking block stop and signature
  Converter->>State: fold text and signature into reasoning item
  Converter->>Client: completed reasoning events
  Converter->>Client: response.completed with reasoning output

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Possibly related PRs

• maximhq/bifrost#5286: Updates Anthropic thinking streaming conversion and reasoning item lifecycle/order coverage.

Suggested reviewers: akshaydeo, tejasghatte, r-droid101, danpiths, roroghost17

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main fix for completing visible thinking items on the streaming Responses surface.
Description check	✅ Passed	The PR description matches the template well, covering summary, changes, testing, related issues, breaking changes, security, and checklist items.
Linked Issues check	✅ Passed	The changes address #5149 by buffering reasoning text, preserving signatures, and fixing completion events and replay behavior.
Out of Scope Changes check	✅ Passed	The added tests and changelog entry are directly related to the fix, with no unrelated or extraneous changes apparent.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

⚔️ Resolve merge conflicts

• Resolve merge conflict in branch fix-responses-stream-thinking-completion

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (2.12.2)

level=error msg="[linters_context] typechecking error: pattern ./...: directory prefix . does not contain main module or its selected dependencies"

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The merge-base changed after approval.

The merge-base changed after approval.

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✅ fus3r
✅ SahilChoudhary22
❌ akshaydeo
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