Windows command transport - executes Playwright via PowerShell/cmd.exe.

This transport avoids WSL2 networking issues by running Node.js Playwright directly on Windows via PowerShell, communicating through stdin/stdout.

Wire protocol

Requests are newline-delimited JSON {id, method, params}; responses are {id, result} or {id, error}. Results carry an explicit envelope:

• {"json": v} - an arbitrary evaluated value (evaluate, cdp_send)
• {"value_b64": b} - base64 binary (screenshot), decoded to a binary
• {"value": s} - a plain string (content)
• {"guid": g} - an object handle (context/page/CDP session)
• {"ok": true} - an action with no return value

Unsolicited {"event": "binding", ...} messages (from expose_binding/4) are routed to the registered Elixir callback rather than dropped.