Keep an opt-out for MCP Apps form deferral on the hosted remote server #3455

PR #3348 removed the remote_mcp_ui_apps flag and made MCP Apps form deferral unconditional for UI-capable clients. Write tools such as issue_write and create_pull_request now hand off to a form before executing.

On claude.ai the form never renders. The write is deferred, nothing appears in the conversation, and the assistant reports that a form is waiting for review and submission — so the call silently does nothing and the user is told to act on a widget that is not there. Issue creation that worked previously no longer does. #3415 reports the same non-rendering; #2823 proposes a capability negotiation gap, which fits: the client appears to advertise UI support well enough for the server to defer, but does not render this app's form.

I have not verified that #3348 is the cause in my case, so this is a request about the configuration surface rather than a bug report.

The request: please keep a usable opt-out.

• Confirm whether mcp_apps_disable_form_deferral is honoured on api.githubcopilot.com/mcp, and document how to set it for clients that cannot send X-MCP-Features or a ?features= query (managed connectors, for example).
• Consider not deferring when the write call already carries complete parameters, along the lines of Skip MCP App form when issue/PR write carries non-form params #2589.
• Consider falling back to direct execution when the form is never acknowledged by the client.

As it stands, a client whose form never renders has no path back to direct execution, since the flag-based opt-out no longer exists.