co-mono/plan.md

Google Cloud Code Assist Provider Implementation Plan

Overview

Add support for Gemini CLI / Antigravity authentication, which uses Google's Cloud Code Assist API (cloudcode-pa.googleapis.com) to access Gemini and Claude models through a unified gateway.

References

• Antigravity API Spec: https://github.com/NoeFabris/opencode-antigravity-auth/blob/main/docs/ANTIGRAVITY_API_SPEC.md
• Gemini CLI Auth: https://github.com/jenslys/opencode-gemini-auth
• Antigravity Auth: https://github.com/NoeFabris/opencode-antigravity-auth

Key Differences from Standard Google Provider

1. Endpoint: cloudcode-pa.googleapis.com/v1internal:streamGenerateContent?alt=sse
2. Auth: OAuth token (not API key)
3. Request format: Wrapped in { project, model, request: {...} }
4. Response format: Wrapped in { response: {...} } (needs unwrapping)
5. Headers: Requires User-Agent, X-Goog-Api-Client, Client-Metadata

OAuth Details

• Client ID: 681255809395-oo8ft2oprdrnp9e3aqf6av3hmdib135j.apps.googleusercontent.com
• Client Secret: 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
• Redirect URI: http://localhost:8085/oauth2callback
• Scopes: cloud-platform, userinfo.email, userinfo.profile
• Token URL: https://oauth2.googleapis.com/token
• Auth URL: https://accounts.google.com/o/oauth2/v2/auth

Available Models

Model ID	Type	Context	Output	Reasoning
gemini-3-pro-high	Gemini	1M	64K	Yes
gemini-3-pro-low	Gemini	1M	64K	Yes
gemini-3-flash	Gemini	1M	64K	No
claude-sonnet-4-5	Claude	200K	64K	No
claude-sonnet-4-5-thinking	Claude	200K	64K	Yes
claude-opus-4-5-thinking	Claude	200K	64K	Yes
gpt-oss-120b-medium	GPT-OSS	128K	32K	No

All models support: text, image, pdf input; text output; cost is $0 (uses Google account quota)

---

Implementation Steps

Phase 1: AI Provider (COMPLETED)

Steps 1-8 completed. The provider is implemented in:

• packages/ai/src/providers/google-cloud-code-assist.ts
• packages/ai/src/providers/google-shared.ts
• Models added to packages/ai/scripts/generate-models.ts

---

Step 1: Update types.ts

File: packages/ai/src/types.ts

Add new API type:

export type Api = "openai-completions" | "openai-responses" | "anthropic-messages" | "google-generative-ai" | "google-cloud-code-assist";

Step 2: Create google-shared.ts

File: packages/ai/src/providers/google-shared.ts

Extract from google.ts:

• convertMessages() - convert internal messages to Gemini Content[] format
• convertTools() - convert tools to Gemini function declarations
• mapToolChoice() - map tool choice to Gemini enum
• mapStopReason() - map Gemini finish reason to our stop reason
• Shared types and imports

Make functions generic to work with both google-generative-ai and google-cloud-code-assist API types.

Step 3: Update google.ts

File: packages/ai/src/providers/google.ts

• Import shared functions from google-shared.ts
• Remove extracted functions
• Keep: createClient(), buildParams(), streamGoogle()

Step 4: Create google-cloud-code-assist.ts

File: packages/ai/src/providers/google-cloud-code-assist.ts

Implement:

export interface GoogleCloudCodeAssistOptions extends StreamOptions {
  toolChoice?: "auto" | "none" | "any";
  thinking?: {
    enabled: boolean;
    budgetTokens?: number;
  };
  projectId?: string; // Google Cloud project ID
}

export const streamGoogleCloudCodeAssist: StreamFunction<"google-cloud-code-assist"> = (
  model: Model<"google-cloud-code-assist">,
  context: Context,
  options?: GoogleCloudCodeAssistOptions,
): AssistantMessageEventStream => {
  // Implementation
};

Key implementation details:

1. Build request body:

   {
     "project": "{projectId}",
     "model": "{modelId}",
     "request": {
       "contents": [...],
       "systemInstruction": { "parts": [{ "text": "..." }] },
       "generationConfig": { ... },
       "tools": [...]
     }
   }
   

2. Headers:

   Authorization: Bearer {accessToken}
   Content-Type: application/json
   Accept: text/event-stream
   User-Agent: google-api-nodejs-client/9.15.1
   X-Goog-Api-Client: gl-node/22.17.0
   Client-Metadata: ideType=IDE_UNSPECIFIED,platform=PLATFORM_UNSPECIFIED,pluginType=GEMINI
   

3. Endpoint: https://cloudcode-pa.googleapis.com/v1internal:streamGenerateContent?alt=sse

4. Parse SSE response:

   • Each line: data: {"response": {...}, "traceId": "..."}
   • Extract response object, which has same structure as standard Gemini response
   • Handle thinking parts with thought: true and thoughtSignature

5. Use shared functions for message/tool conversion and stop reason mapping

Step 5: Update stream.ts

File: packages/ai/src/stream.ts

Add case for new provider:

import { streamGoogleCloudCodeAssist } from "./providers/google-cloud-code-assist.js";

// In the switch/case or if/else chain:
case "google-cloud-code-assist":
  return streamGoogleCloudCodeAssist(model, context, {
    ...options,
    // map reasoning to thinking config
  });

Step 6: Update models.ts

File: packages/ai/src/models.ts

Add to xhighSupportedModels if applicable (check if any models support xhigh).

Step 7: Add models to generate-models.ts

File: packages/ai/scripts/generate-models.ts

Add hardcoded models:

const googleCloudCodeAssistModels: Model<"google-cloud-code-assist">[] = [
  {
    id: "gemini-3-pro-high",
    provider: "google-cloud-code-assist",
    api: "google-cloud-code-assist",
    name: "Gemini 3 Pro High",
    contextWindow: 1048576,
    maxOutputTokens: 65535,
    pricing: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
    input: ["text", "image", "pdf"],
    output: ["text"],
    reasoning: true,
  },
  // ... other models
];

Step 8: Update index.ts exports

File: packages/ai/src/index.ts

Export new provider:

export { streamGoogleCloudCodeAssist, type GoogleCloudCodeAssistOptions } from "./providers/google-cloud-code-assist.js";

---

Phase 2: OAuth Flow in coding-agent

Step 9: Create google-cloud.ts OAuth handler

File: packages/coding-agent/src/core/oauth/google-cloud.ts

Implement:

import { createHash, randomBytes } from "crypto";
import { createServer } from "http";
import { type OAuthCredentials, saveOAuthCredentials } from "./storage.js";

const CLIENT_ID = "681255809395-oo8ft2oprdrnp9e3aqf6av3hmdib135j.apps.googleusercontent.com";
const CLIENT_SECRET = "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";
const REDIRECT_URI = "http://localhost:8085/oauth2callback";
const SCOPES = [
  "https://www.googleapis.com/auth/cloud-platform",
  "https://www.googleapis.com/auth/userinfo.email",
  "https://www.googleapis.com/auth/userinfo.profile",
];
const AUTH_URL = "https://accounts.google.com/o/oauth2/v2/auth";
const TOKEN_URL = "https://oauth2.googleapis.com/token";

export async function loginGoogleCloud(
  onAuth: (info: { url: string; instructions?: string }) => void,
  onProgress?: (message: string) => void,
): Promise<OAuthCredentials & { projectId?: string }> {
  // 1. Generate PKCE
  // 2. Start local server on port 8085
  // 3. Build auth URL and call onAuth
  // 4. Wait for callback with code
  // 5. Exchange code for tokens
  // 6. Discover/provision project via loadCodeAssist endpoint
  // 7. Return credentials with projectId
}

export async function refreshGoogleCloudToken(refreshToken: string): Promise<OAuthCredentials> {
  // Refresh token flow
}

// Project discovery
async function discoverProject(accessToken: string): Promise<string> {
  // Call /v1internal:loadCodeAssist to get project ID
  // Or /v1internal:onboardUser if needed
}

Step 10: Update oauth/index.ts

File: packages/coding-agent/src/core/oauth/index.ts

• Add "google-cloud" to SupportedOAuthProvider
• Add to getOAuthProviders() list
• Add case in login() function
• Add case in refreshToken() function

Step 11: Update oauth/storage.ts

File: packages/coding-agent/src/core/oauth/storage.ts

Extend OAuthCredentials to include optional projectId:

export interface OAuthCredentials {
  type: "oauth";
  refresh: string;
  access: string;
  expires: number;
  enterpriseUrl?: string;
  projectId?: string;  // For Google Cloud
}

Step 12: Update model-config.ts

File: packages/coding-agent/src/core/model-config.ts

Add logic to get API key for google-cloud-code-assist provider:

• Check for OAuth token via getOAuthToken("google-cloud")
• Return the access token as the "API key"

---

Phase 3: Testing

Manual Testing

1. Run pi and use /login to authenticate with Google
2. Select a google-cloud-code-assist model
3. Send a message and verify streaming works
4. Test tool calling
5. Test thinking models

Verification Points

• OAuth flow completes successfully
• Token refresh works
• Streaming text works
• Thinking blocks are parsed correctly
• Tool calls work
• Tool results are sent correctly
• Error handling works (rate limits, auth errors)

---

Notes

systemInstruction Format

Must be object with parts, NOT plain string:

{
  "systemInstruction": {
    "parts": [{ "text": "You are a helpful assistant." }]
  }
}

Tool Name Rules

• Must start with letter or underscore
• Allowed: a-zA-Z0-9, underscores, dots, colons, dashes
• Max 64 chars
• No slashes or spaces

Thinking Config

{
  "generationConfig": {
    "thinkingConfig": {
      "thinkingBudget": 8000,
      "includeThoughts": true
    }
  }
}

Response Unwrapping

SSE lines come as:

data: {"response": {...}, "traceId": "..."}

Need to extract response object which matches standard Gemini format.