fix: use dummy thought_signature for cross-model Gemini function calls#2155
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dgageot merged 1 commit intodocker:mainfrom Mar 18, 2026
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Assessment: 🟢 APPROVE
No issues found. The implementation correctly:
- Uses
len(sig) > 0to handle both nil and empty byte slices - Applies the thought signature consistently to all parts (text and function calls)
- Includes comprehensive test coverage for all edge cases
- Follows the Google-documented approach for cross-model function call replay
The fix properly addresses the INVALID_ARGUMENT error when replaying non-Gemini tool calls to Gemini models.
Gemini 3+ models require a thought_signature on functionCall parts. When conversation history is generated by a non-Gemini model (e.g. Anthropic during per-tool model routing), no signature exists, causing a 400 INVALID_ARGUMENT error. Use the Google-documented sentinel value "skip_thought_signature_validator" as a fallback when the original message has no ThoughtSignature. Assisted-By: docker-agent
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gtardif
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Mar 18, 2026
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Problem
When a tool has a per-tool model override set to a Gemini 3+ model (e.g.
google/gemini-3.1-flash-lite-preview) while the main agent uses a different provider (e.g. Anthropic Haiku), the Gemini API returns a 400 INVALID_ARGUMENT error:This happens because the main model generates assistant messages with tool calls that have no
ThoughtSignature(a Gemini-specific concept). When the conversation history is replayed to Gemini during per-tool model routing, it rejects the function call parts.Fix
Use the Google-documented sentinel value
"skip_thought_signature_validator"as a fallback when the original message has noThoughtSignature. This tells the Gemini API to skip signature validation for replayed history.See: https://ai.google.dev/gemini-api/docs/thought-signatures
Changes
pkg/model/provider/gemini/client.go: AddedthoughtSignatureOrDefault()helper that returns the real signature when present, or the skip sentinel otherwise. Applied in the tool-call conversion path.pkg/model/provider/gemini/client_test.go: Added table-driven tests covering: real signature preserved, nil signature fallback, empty (non-nil) signature fallback, and multiple tool calls with text.