ReceiveAsync suspended the mailbox for the whole of every handler, so one Test Connect against a
black-holed PLC (60 s clamp) or one large deploy compose stalled every other admin operation
fleet-wide — AdminUI alarm acks/shelves, driver restarts, the next deploy.
- TestDriverConnect runs the probe on the thread pool and pipes a TestDriverConnectResult
straight to the requester (every path yields a result, never Status.Failure).
- StartDeployment serialises only the in-flight check (DB row + an actor-local compose-in-flight
flag, because the Deployment row is written at the END of the compose); the snapshot read,
validation, gzip and row write run off-actor and return as DeployComposed /
DeployComposeFailed, where the coordinator is told and the requester answered.
Tests: an alarm ack completes in < 1 s while a 60 s probe is pending and while a compose is
parked on a gated DbContext (positive controls: both still complete afterwards); a second
StartDeployment during an in-flight compose is refused.
Refs #733
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty
ae84253773