Concepts
Prerequisites
A prerequisite is a task that has to finish before another task can start. This is how a workflow enforces its order instead of relying on people to remember it.
How they work
Draw a line from one task to another in the builder and you have said: the second one waits for the first one.
On a checklist, the second task shows as Blocked, with a line reading "Waiting on Deploy job". Nobody can work it yet. When the first task closes, the second turns Ready on its own — no one has to release it.
A task with no prerequisites is Ready from the moment the checklist is generated.
Several prerequisites
A task can wait on more than one. It stays blocked until every one of them has closed, and its "Waiting on" line names what is still outstanding.
Things that happen at the same time
Two tasks that share the same prerequisite both turn Ready together, and either can be done first. This is how you say "these two can happen in parallel" — give them the same predecessor and no line between them.
The Production deploy workflow does exactly this: prep-release unblocks both
run-migrations and flip-flags, and ci-deploy waits for both of them.
Skipping still unblocks
A skipped task counts as closed for this purpose. Skip a task and everything waiting on it turns Ready, exactly as if it had been completed.
That is deliberate — it means Skip is a safe way past a task that does not apply this time, rather than something that strands the rest of the checklist.
Circular prerequisites
If A waits on B and B waits on A, neither can ever start. The builder catches this and refuses to publish until you break the loop.