The canvas agent is in whitelisted beta — these changes are visible only on accounts that have it enabled.
The task card waits for your media
The agent prepares the nodes; what actually starts them is you hitting Generate all.
During that window the card now reads “Media still generating · N still running”, and only switches to “Task complete” once every node from this round has finished. Same when a run fails or is stopped — as long as something is still running, the card will not claim it is done.
Only this round counts
The count covers only the nodes this round of the agent created. Anything you started by hand elsewhere on the canvas is excluded, so the number always means “what is left in this task”.
Stopping one of them
There is deliberately no stop button on the card: these are canvas generations, so stop them on the node itself.