#1313
跨api格式搜索转换，并且保留citations

Greptile Summary

This PR adds end-to-end preservation of search citations and annotations across all four transformer layers (OpenAI Responses, OpenAI Chat, Anthropic, and Gemini), enabling citation round-trips when a request passes through multiple provider adapters.

• OpenAI Responses: outbound_convert.go and outbound_stream.go extract web_search_call items into TransformerMetadata and track per-content-part annotation offsets using utf8.RuneCountInString; inbound.go converts llm.Annotation back to Responses API Annotation objects and restores web_search_call output items from metadata.
• Anthropic: outbound_convert.go extracts TextCitation from text blocks into llm.Annotation, and preserves native provider content blocks (including server_tool_use/web_search_tool_result) via TransformerMetadata; inbound_stream.go buffers pending citations and flushes them as citations_delta events just before the text block closes.
• Gemini: outbound_convert.go derives llm.Annotation from both CitationMetadata and GroundingMetadata; inbound_convert.go converts annotations back to CitationMetadata and maps llm.ToolTypeWebSearch to GoogleSearch.

Confidence Score: 5/5

Safe to merge — the core citation round-trip logic is well-tested across all four transformer layers with no correctness regressions found.

The streaming metadata fallback path in outbound_stream.go properly handles the case where web search call metadata exists but no annotations are emitted, closing the gap flagged in prior review. All other new code paths (Anthropic citation buffering/flushing, Gemini annotation derivation, Responses API annotation offset tracking) have corresponding unit and integration tests, and the logic checks out under manual inspection.

No files require special attention beyond the minor comment wording in llm/transformer/openai/model.go.

Important Files Changed

Sequence Diagram

sequenceDiagram
    participant Client
    participant ResponsesOutbound as Responses Outbound (OAI→LLM)
    participant LLMResponse as llm.Response
    participant AnthropicInbound as Anthropic Inbound (LLM→Anthropic)
    participant GeminiInbound as Gemini Inbound (LLM→Gemini)

    Note over ResponsesOutbound: web_search_call OutputItemDone
    ResponsesOutbound->>LLMResponse: TransformerMetadata["openai_responses_web_search_calls"]

    Note over ResponsesOutbound: message OutputItemDone (with annotations)
    ResponsesOutbound->>LLMResponse: Choices[0].Delta.Annotations + TransformerMetadata emitted

    Note over ResponsesOutbound: response.completed (fallback)
    ResponsesOutbound->>LLMResponse: TransformerMetadata emitted if not yet sent

    LLMResponse->>AnthropicInbound: message.Annotations + TransformerMetadata
    AnthropicInbound->>AnthropicInbound: "citationFromLLMAnnotation()<br/>(url_citation to web_search_result_location if OAI web search metadata present)"
    AnthropicInbound->>AnthropicInbound: "mergeAnthropicResponseContentBlocks()<br/>(restore native provider blocks from metadata)"
    AnthropicInbound-->>Client: Anthropic Message with citations

    LLMResponse->>GeminiInbound: message.Annotations
    GeminiInbound->>GeminiInbound: citationMetadataFromLLMAnnotations()
    GeminiInbound-->>Client: Gemini GenerateContentResponse with CitationMetadata

_{Reviews (3): Last reviewed commit: "fix: preserve responses web search calls..." | Re-trigger Greptile}

这个牛逼。