feat(ai,coding-agent): add Anthropic Claude support to Google Vertex AI provider - #9993

Problem

In Google Cloud Vertex AI Model Garden, users can access Anthropic Claude models (such as Claude Opus, Claude Sonnet, and Claude Haiku) using their Google Cloud credentials (ADC or API key). Previously, the google-vertex catalog generator explicitly excluded all non-Gemini models with if (!modelId.startsWith("gemini-")) continue;, and the provider only exposed the google-vertex Gemini API. As a result, users with GCP credentials authorized for Claude models could only view and invoke Gemini models.

Solution

1. Model Catalog Generation (packages/ai/scripts/generate-models.ts):

   • Updated processGoogleModels so claude-* models under google-vertex are included with api: "anthropic-messages", provider: "google-vertex", and base URL https://{location}-aiplatform.googleapis.com.
   • Claude models inherit proper tool-calling, vision modalities, reasoning options, and cost metadata.

2. Vertex Anthropic Adapter (packages/ai/src/api/vertex-anthropic.ts, packages/ai/src/api/vertex-anthropic.lazy.ts):

   • Implemented a request adapter for Anthropic Messages on Vertex AI.
   • Obtains Google Cloud OAuth authorization headers from Application Default Credentials / service account files or Google Cloud API keys via @google/genai without adding new dependencies.
   • Rewrites messages requests to the Vertex AI publisher endpoint format:
     https://${location}-aiplatform.googleapis.com/v1/projects/${project}/locations/${location}/publishers/anthropic/models/${modelId}:${stream ? "streamRawPredict" : "rawPredict"}
   • Formats the request body for Vertex AI (removes model from JSON body, sets "anthropic_version": "vertex-2023-10-16").
   • Injects Google authorization headers (Authorization: Bearer <token> or x-goog-api-key: <key>) while stripping Anthropic-specific API key headers.
   • Connects to anthropic-messages.ts streaming machinery so tool use, extended thinking, streaming deltas, and usage calculations work identically.

3. Tree-Shaking & Bundle Isolation:

   • The Vertex adapter is exposed as a lazy API module (vertex-anthropic.lazy.ts).
   • anthropic-messages.ts remains decoupled from @google/genai, preserving browser bundle tree-shaking for anthropicProvider().

4. Provider Dispatch (packages/ai/src/providers/google-vertex.ts):

   • Configured googleVertexProvider with an API dispatch map for "google-vertex" (Gemini) and "anthropic-messages" (Vertex Claude).

Verification

• npm run check: full check passed (biome formatting, linting, imports, runtime dependencies, shrinkwrap, install lock, TypeScript checks, and browser smoke check).
• vitest --run packages/ai/test/vertex-anthropic.test.ts: all 10 tests passed covering catalog verification, provider dispatch, request URL/header/body transformation, error handling, and streaming.
• Existing tests in packages/ai/test/google-vertex-api-key-resolution.test.ts and packages/ai/test/providers.test.ts pass.