Migration — Phase 67: Gemini AI Provider

Shape: Additive opt-in companion. No consumer migration required.

What changes

A new NuGet companion ToolUp.AIProviders.Gemini ships alongside ToolUp.AIProviders.Claude and ToolUp.AIProviders.OpenAI. The companion implements IAIProvider against Google's Generative Language API (v1beta), supports the gemini-2.5-* and gemini-1.5-* model families, and is BYOK-capable via ISecretStore under the _platform scope key GEMINI_API_KEY.

No SDK interfaces changed. No existing-provider code touched. No consumer is required to do anything — consumers wishing to expose Gemini add the package reference and append a builder to the DefaultAIProviderFactory.create builders list.

Diff to apply (opt-in)

A consumer that wants to offer Gemini alongside its existing providers adds:

<!-- Server csproj / fsproj -->
<PackageReference Include="ToolUp.AIProviders.Gemini" />

…and appends a builder entry to the deployment's compose step. The shape is the same as Claude / OpenAI:

open GeminiAIProvider

let geminiBuilder = {
    Descriptor = {
        Id = ProviderId
        DisplayName = "Google Gemini"
        SupportedModels = KnownModels
        DefaultModel = DefaultModel
        Capabilities = {
            AIProviderCapabilities.unknown with
                Streaming = true
                ToolUse = true
                Vision = true
                SupportsPromptCaching = true
                ProviderName = "google-gemini"
                Model = DefaultModel
        }
    }
    Build = fun apiKey model -> createWithApiKeyAndModel apiKey model
}

// Then in the existing builder list:
DefaultAIProviderFactory.create
    [ ClaudeAIProvider.builder
      OpenAIProvider.builder
      geminiBuilder ]    // append; existing entries unchanged
    providerProfile
    secretStore
    fallbackPolicy
    platformProvider

Store the API key under _platform scope, name GEMINI_API_KEY.

Verification steps

• dotnet build of the consuming app remains clean (additive <PackageReference>).
• A user-configured Gemini ProviderEntry resolves via IAIProviderFactory.Resolve and serves a models/gemini-2.5-flash or models/gemini-2.5-pro completion.
• Streaming, tool use, and multimodal input round-trip in the same forge-internal shape as Claude / OpenAI for the same inputs (semantically equivalent — exact bytes differ per vendor wire format).
• /health/ready includes a ai_provider:google-gemini probe verifying the secret-store key is set.

Rollback

Remove the <PackageReference> + the appended builder entry. No data, schema, or stored-config migration is involved — the SDK's IProviderProfile quietly ignores entries whose ProviderId no longer matches a registered builder (surfaced as UnknownProvider per the existing ProviderResolutionError contract).