rpc-ui sets hasUI=true which causes the bash tool to take the
runInteractiveBashPty path when pty=true. RpcExtensionUIContext.custom()
is a stub returning undefined, so result.cancelled dereferences undefined
and throws. PTY bash requires a live TUI overlay; rpc-ui only provides
dialog-style UI. Set PI_NO_PTY for rpc-ui so the usePty guard in
bash.ts stays false.
