Create or reconnect to a PTY session.

Looks up the PTY session identified by the path session_name and either reconnects to the existing session or creates it if it does not yet exist. The session_name is a client-chosen session identifier, not an opaque server-issued ID. It must be non-empty (1..=256 chars) and use only ASCII letters, digits, '-' and '_'. A newly created PTY session starts an interactive bash shell on the Devbox. Optional cols and rows query parameters apply an initial terminal size before any I/O; they must both be present and in the range 1..=1000 to take effect. The response returns a PtyConnectView containing connect_url (a server-relative path to the WebSocket data plane), idle_ttl_seconds (how long this session is retained after the last client disconnects), and the resulting cols/rows. The interactive byte stream itself is intentionally not modeled in OpenAPI; see the controller-level documentation for the WebSocket close-code conventions. The single-attach contract is enforced when a client opens the WebSocket data plane, not on this bootstrap call: bootstrap always succeeds for a valid session_name, even if another client is currently attached. Rejection of a second concurrent attach happens at WebSocket upgrade time. If the active client disconnects, the session is preserved for the idle TTL so a later connect using the same session_name resumes the same shell. After the TTL expires, after an explicit close control action, or after the underlying Devbox lifecycle replaces the PTY process (such as through suspend/resume), a later request with the same session_name creates a fresh PTY session without the previous shell state.

Documentation note: this operation is published from mux strictly as an OpenAPI contract stub for the PTY service control plane. It is not evidence that mux itself serves the interactive PTY transport.