Function decode_launch_settings 

pub(crate) fn decode_launch_settings(
    value: Value,
) -> Result<SessionLaunchSettings>

Decode launch settings off the dispatcher channel. Symmetric to the encode-side ?-propagation in AgentHandle::new_session.

A failure refuses the spawn (Ved, 2026-10-15). The settings carry the blocked-tools denial (disallowedTools) among the rest, so a spawn on defaults would start a session WIDER than the one that was configured - silently unblocking tools. The decode runs in the BRIDGE, where a refusal goes on the same event every other spawn failure does (ConnectionFailed), so the seat records the failure and rolls its row instead of sitting at Spawning with nothing to say.