Claude and GPT-OSS fail in OpenCode although the official Antigravity CLI succeeds #20

Summary

Google AI Pro accounts can use Claude Sonnet 4.6 and GPT-OSS 120B through Google Antigravity's official CLI, but the same accounts fail through @cortexkit/opencode-antigravity-auth 2.2.1 in OpenCode.

This is related to #19, but affects the non-Gemini models and account failover path.

Environment

• Windows 11
• OpenCode 1.18.23
• @cortexkit/opencode-antigravity-auth 2.2.1
• Seven configured Google accounts
• Google AI Pro entitlement on the relevant accounts

Control test: official Antigravity CLI succeeds

Both commands returned exactly OK:

agy --print='Reply exactly: OK' --model claude-sonnet-4-6 --print-timeout 60s
agy --print='Reply exactly: OK' --model gpt-oss-120b-medium --print-timeout 60s

agy models also lists these models for the authenticated account.

OpenCode repro

opencode run -m google/antigravity-claude-sonnet-4-6-thinking 'Reply exactly: OK' --format json --log-level ERROR

The plugin traverses the pool and the Antigravity endpoint returns 429 RESOURCE_EXHAUSTED for every account. It then reports every account as rate-limited and OpenCode remains on its Thinking UI for a long time while the serial attempts run.

The analogous GPT-OSS OpenCode request also received RESOURCE_EXHAUSTED for every account, despite the official agy command succeeding immediately.

Additional diagnostic

The project context selected by the plugin differs from the context used by agy. A controlled override to the official CLI project changed the plugin failure to:

403 PERMISSION_DENIED
SUBSCRIPTION_REQUIRED (#3501)

That demonstrates the issue is in request/project/entitlement emulation, not plan eligibility or exhausted Google AI Pro quota. The override was reverted after the test.

Expected

For a Google AI Pro account where the official Antigravity CLI can complete these requests, OpenCode should complete the same request. When an account genuinely returns quota exhaustion, the plugin should promptly rotate to another usable account and surface a final error only after the pool is exhausted.

Requested investigation

1. Reconcile the plugin's project-context resolution and request metadata with the current official agy CLI for Claude and GPT-OSS.
2. Treat SUBSCRIPTION_REQUIRED (#3501) and model-specific eligibility failures as explicit, diagnosable outcomes rather than a long Thinking state.
3. Confirm account-pool rotation semantics for non-Gemini models.

No OAuth tokens, account emails, project identifiers, or raw tool payloads are included. The full tool-payload error dump is separately tracked by #18.