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fix: strip -customtools variant suffix for provider and auth lookup #1958

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fix: strip -customtools variant suffix for provider and auth lookup #1958

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24 changes: 24 additions & 0 deletions internal/registry/model_registry.go
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Original file line number Diff line number Diff line change
Expand Up @@ -742,9 +742,33 @@ func (r *ModelRegistry) ClientSupportsModel(clientID, modelID string) bool {
}
}

// Fallback: strip known model variant suffixes (e.g. "-customtools").
// These variants share the same provider as the base model.
if stripped := stripModelVariantSuffix(modelID); stripped != modelID {
for _, id := range models {
if strings.EqualFold(strings.TrimSpace(id), stripped) {
return true
}
}
}

return false
}

// knownModelVariantSuffixes lists suffixes that Google appends to model names
// for specialised fine-tune variants (e.g. "-customtools" for tool-calling).
// These variants share the same provider/executor as the base model.
var knownModelVariantSuffixes = []string{"-customtools"}

func stripModelVariantSuffix(model string) string {
for _, suffix := range knownModelVariantSuffixes {
if strings.HasSuffix(model, suffix) {
return strings.TrimSuffix(model, suffix)
}
}
return model
}
Comment on lines +758 to +770
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@gemini-code-assist gemini-code-assist bot Mar 8, 2026

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high

This helper function and the knownModelVariantSuffixes variable are also defined in sdk/api/handlers/handlers.go. To avoid code duplication and improve maintainability, they should be moved to a shared package. The internal/thinking/suffix.go file seems like a suitable location, as it already handles model name suffix parsing. You would then need to add an import for internal/thinking in this file and use the shared function.


// GetAvailableModels returns all models that have at least one available client
// Parameters:
// - handlerType: The handler type to filter models for (e.g., "openai", "claude", "gemini")
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27 changes: 27 additions & 0 deletions sdk/api/handlers/handlers.go
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Original file line number Diff line number Diff line change
Expand Up @@ -801,6 +801,19 @@ func (h *BaseAPIHandler) getRequestDetails(modelName string) (providers []string
providers = util.GetProviderName(resolvedModelName)
}

// Fallback: strip known model variant suffixes (e.g. "-customtools") for
// provider lookup. The suffix is also stripped from resolvedModelName
// because CPA routes gemini-cli through cloudcode-pa/v1internal (OAuth)
// which does not accept variant suffixes (returns 404).
// The behavioral difference is minor: -customtools only changes tool
// selection priority (prefers custom tools over bash), not model capabilities.
if len(providers) == 0 {
if stripped := stripModelVariantSuffix(baseModel); stripped != baseModel {
providers = util.GetProviderName(stripped)
resolvedModelName = stripModelVariantSuffix(resolvedModelName)
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@gemini-code-assist gemini-code-assist bot Mar 8, 2026

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critical

There's a potential bug here. The stripModelVariantSuffix function uses strings.HasSuffix to find and remove the variant suffix. If resolvedModelName contains a thinking suffix (e.g., (8192)), strings.HasSuffix will fail to find the variant suffix (e.g., -customtools), and resolvedModelName will not be stripped as intended. This would cause issues with providers that don't accept variant suffixes.

A more robust way to strip the variant suffix while preserving the thinking suffix would be to replace the baseModel part within resolvedModelName with the stripped version.

Suggested change
resolvedModelName = stripModelVariantSuffix(resolvedModelName)
resolvedModelName = strings.Replace(resolvedModelName, baseModel, stripped, 1)

}
}

if len(providers) == 0 {
return nil, "", &interfaces.ErrorMessage{StatusCode: http.StatusBadGateway, Error: fmt.Errorf("unknown provider for model %s", modelName)}
}
Expand All @@ -810,6 +823,20 @@ func (h *BaseAPIHandler) getRequestDetails(modelName string) (providers []string
return providers, resolvedModelName, nil
}

// knownModelVariantSuffixes lists suffixes that Google appends to model names
// for specialised fine-tune variants (e.g. "-customtools" for tool-calling).
// These variants share the same provider/executor as the base model.
var knownModelVariantSuffixes = []string{"-customtools"}

func stripModelVariantSuffix(model string) string {
for _, suffix := range knownModelVariantSuffixes {
if strings.HasSuffix(model, suffix) {
return strings.TrimSuffix(model, suffix)
}
}
return model
}
Comment on lines +826 to +838
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@gemini-code-assist gemini-code-assist bot Mar 8, 2026

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high

This helper function and the knownModelVariantSuffixes variable are duplicated from internal/registry/model_registry.go. To avoid code duplication and improve maintainability, they should be moved to a shared package like internal/thinking/suffix.go. Since this file already imports the thinking package, you can remove this duplicated code and call the function from there.


func cloneBytes(src []byte) []byte {
if len(src) == 0 {
return nil
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