pub fn use_launcher_endpoints(
state: &Arc<AppState>,
) -> Option<Result<BackendSpawnResult, String>>Expand description
Phase B.1: when the launcher has already spawned srv (env var
AGENTMUX_BACKEND_WS is set), populate state from the env vars
the launcher passed and return Ok — no need to spawn srv ourselves.
Returns Ok(BackendSpawnResult) mirroring the shape of
spawn_backend so the caller in main.rs is symmetric. Returns
Err only if env vars are present but malformed; if they’re
absent the caller should fall through to spawn_backend (the
task dev path where the launcher isn’t in the loop).