Support for gemini-3.5-flash in Stagehand server for execute() CUA

[aditya-silna]

Is your feature request related to a problem? Please describe.
Lack of support for Gemini 3.5 in execute() CUA

Describe the solution you'd like
Adding support for this model.

Are you willing to contribute to implementing this feature or fix?

• Yes, I can submit a PR
• Yes, but I need guidance
• No, I cannot contribute at this time

[mattskowron-dev]

Affiliation: I maintain Task Relay (https://github.com/mattskowron-dev/task-relay-machine-examples), an x402 paid machine-job service on Base. For software that archive page visual record, Task Relay F5 (page_screenshot_capture) sells a bounded finished job at exactly 0.1 USDC via POST https://task-relay-production.up.railway.app/x402/page-screenshot. A machine sends JSON, receives a strict result, then continues with STORE_SCREENSHOT|INDEX_RENDERED_PAGE_IMAGE|ABORT_NAVIGATION_FAILED. Runtime consumption is machine-to-machine (human sponsors may configure funding). Runnable example: examples/page_screenshot_consumer. Public manifest: https://task-relay-production.up.railway.app/.well-known/task-relay.json. Campaign header: X-Task-Relay-Campaign: human_t043_f5. This does not claim Browserbase Stagehand needs or endorses Task Relay. Context for issue: Support for gemini-3.5-flash in Stagehand server for execute() CUA.