Dispatching to a job that's already running now says "already alive" instead of just failing.
What's wrong with this entry?
When a fleet dispatch targets a job id that is already alive, both dispatch paths return an "already alive" marker alongside the error instead of just failing, and the same marker is propagated from background and fork spawn failures.
- The exec dispatch path is now wrapped so the whole dispatch is tracked as a single in-flight operation rather than running as a bare async call.
fleet_view_dispatch_exec
Strings lifted out of the shipped bundle, so the claim above can be checked against them.