fix(translation): report content filter stops as Anthropic refusal

[Atharva-Kanherkar]

What

• Translate OpenAI content_filter stops to Anthropic refusal in buffered and streaming responses.
• Emit the required Anthropic stop_details object for synthesized refusals.
• Decode Anthropic refusal back to the normalized content-filter reason.
• Normalize streamed Anthropic refusals as StopReason::ContentFilter when responses are accumulated.
• Translate streamed Anthropic refusals to OpenAI content_filter.
• Add buffered, streaming, and accumulator regression coverage.

Why

An OpenAI-compatible backend could stop generation because of content filtering, but Anthropic clients received end_turn. That made a filtered or truncated response indistinguishable from a normal completion.

The normalized response already preserves this condition as StopReason::ContentFilter. The loss occurred when the Anthropic codecs encoded the stop reason. Anthropic documents refusal for safety refusals and requires a stop_details object, so the translated response now preserves the relevant meaning with a valid Anthropic shape.

Error and Unknown remain mapped to end_turn and are outside this change.

Closes #369

Validation

• cargo fmt --all --check
• cargo clippy --ignore-rust-version -p switchyard-protocol -p switchyard-translation --all-targets -- -D warnings
• cargo test --ignore-rust-version -p switchyard-protocol: 18 unit tests and 2 documentation tests passed
• cargo test --ignore-rust-version -p switchyard-translation: 119 tests passed
• Commitlint across all three PR commits: 0 problems and 0 warnings

The full workspace test run is blocked locally while linking the existing switchyard-py PyO3 cdylib because of a macOS deployment-target mismatch in aws-lc-sys. The same linker failure reproduces on a clean tree. CI runs the workspace suite on Linux.

The local Rust commands use --ignore-rust-version because the available Homebrew compiler is Rust 1.96.0 while the repository declares Rust 1.96.1.

[coderabbitai]

Walkthrough

The codecs now preserve moderation stop reasons across OpenAI Chat and Anthropic translations. Buffered and streaming paths map content_filter and refusal in both directions. Regression tests cover both response conversions.

Changes

Moderation stop translation

Layer / File(s)	Summary
Stop-reason mapping crates/switchyard-translation/src/codecs/anthropic/buffered.rs, crates/switchyard-translation/src/codecs/anthropic/stream.rs, crates/switchyard-translation/src/codecs/openai_chat/stream.rs	Buffered and streaming codecs map StopReason::ContentFilter to Anthropic refusal and OpenAI Chat content_filter.
Translation regression tests crates/switchyard-translation/tests/response_translation.rs	Tests verify OpenAI Chat content_filter and Anthropic refusal translate in both directions.

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

Poem

I’m a rabbit with mappings so neat,
Refusals and filters now meet.
Through streams they both hop,
No reason can drop,
And tests make the pathway complete. 🐇

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes preserve the content-filter distinction by mapping it to Anthropic refusal and add tests for both translation directions [#369].
Out of Scope Changes check	✅ Passed	All code and test changes directly support content-filter stop-reason translation and the linked issue [#369].
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: translating content-filter stops to Anthropic refusal reasons.

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[coderabbitai]

🧹 Nitpick comments (1)

crates/switchyard-translation/tests/response_translation.rs (1)

603-631: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Add streaming regression tests for content_filter and refusal in both directions. The stream tests cover other stop reasons but not these mappings.

🤖 Prompt for 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.

In `@crates/switchyard-translation/tests/response_translation.rs` around lines 603
- 631, Add streaming regression tests alongside the existing stream translation
tests for both content_filter and refusal mappings: verify OpenAI Chat
content_filter becomes Anthropic refusal, and Anthropic refusal becomes the
corresponding OpenAI streaming finish reason. Reuse the established streaming
test helpers and assertions, preserving the non-streaming behavior covered by
openai_content_filter_translates_to_anthropic_refusal.

🤖 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.

Nitpick comments:
In `@crates/switchyard-translation/tests/response_translation.rs`:
- Around line 603-631: Add streaming regression tests alongside the existing
stream translation tests for both content_filter and refusal mappings: verify
OpenAI Chat content_filter becomes Anthropic refusal, and Anthropic refusal
becomes the corresponding OpenAI streaming finish reason. Reuse the established
streaming test helpers and assertions, preserving the non-streaming behavior
covered by openai_content_filter_translates_to_anthropic_refusal.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 3a07a621-f3cd-4fac-955b-bc722e52d147

📥 Commits

Reviewing files that changed from the base of the PR and between 58f355a and ced15b3.

📒 Files selected for processing (4)

• crates/switchyard-translation/src/codecs/anthropic/buffered.rs
• crates/switchyard-translation/src/codecs/anthropic/stream.rs
• crates/switchyard-translation/src/codecs/openai_chat/stream.rs
• crates/switchyard-translation/tests/response_translation.rs

[Atharva-Kanherkar]

hi @nachiketb-nvidia, i have loved using switchyard. i ran into this bug and put together a small fix. if you have time, could you please take a look? thank you!