Greptile Summary

This PR removes the "signature prefix marker" mechanism, which previously embedded a per-channel footprint (derived from AccountIdentity = strconv.Itoa(c.ID)) into reasoning signatures via TransportScope. The new approach replaces footprint-based encoding/decoding with content-based provider detection (GuessSignatureProvider), where Anthropic signatures are identified by EqQ/Eqo/Eqr prefixes and Gemini signatures by protobuf structure. All transformers now emit Metadata: nil and AccountIdentity is removed from every config except ClaudeCode.

• The integration test for "reasoning request" drops a lo.Filter that was previously stripping reasoning-type items from the expected payload before comparison — meaning reasoning items from prior turns now pass through in the outbound request, which is an important behavior change worth validating end-to-end.
• DecodeAnthropicSignature now passes through any signature whose provider is Unknown (not just Anthropic), meaning a cross-provider signature that cannot be recognized will silently succeed rather than be dropped; conversely, DecodeGeminiThoughtSignature now only returns a signature identified as Gemini (dropping Unknown), which is the opposite policy.

Confidence Score: 4/5

Safe to merge with care — the behaviour changes around reasoning item pass-through and Unknown-signature handling are intentional but worth validating in a staging environment.

Only P2 findings in this review, but the PR carries significant behaviour changes (reasoning items now pass through into Responses API payloads, all provider-signature round-trips now rely on content-based heuristics rather than per-channel footprints) that warrant careful staging validation. Previous review threads flagged P1 concerns around looksLikeProto classification and ClaudeCode deterministic identity; the new looksLikeProto implementation is substantially more robust (full structural validation), but the overall risk profile of cross-provider signature routing keeps confidence at 4.

llm/transformer/shared/signature.go (GuessSignatureProvider heuristics — new trust anchor for all cross-provider routing), llm/transformer/openai/responses/integration_test.go (reasoning item pass-through behaviour change), llm/transformer/gemini/outbound_convert.go (Unknown-signature fallback to ContextEngineeringThoughtSignature)

Important Files Changed

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[ReasoningSignature blob] --> B{GuessSignatureProvider}
    B -->|starts with gAAAA / gAAA| C[ProviderOpenAI]
    B -->|starts with EqQ / Eqo / Eqr| D[ProviderAnthropic]
    B -->|std base64 AND looksLikeProto| E[ProviderGemini]
    B -->|anything else| F[ProviderUnknown]

    C -->|DecodeAnthropicSignature| G[nil - rejected]
    D -->|DecodeAnthropicSignature| H[raw value - accepted]
    E -->|DecodeAnthropicSignature| G
    F -->|DecodeAnthropicSignature| H

    C -->|DecodeGeminiThoughtSignature| I[nil - rejected]
    D -->|DecodeGeminiThoughtSignature| I
    E -->|DecodeGeminiThoughtSignature| J[raw value - accepted]
    F -->|DecodeGeminiThoughtSignature| I

    C -->|DecodeOpenAIEncryptedContent| K[raw value - accepted]
    D -->|DecodeOpenAIEncryptedContent| L[nil - rejected]
    E -->|DecodeOpenAIEncryptedContent| L
    F -->|DecodeOpenAIEncryptedContent| K

_{Reviews (5): Last reviewed commit: "refactor: remove the signature prefix ma..." | Re-trigger Greptile}