pallet-scheduler: Put back postponed tasks into the agenda

[bkchr]

Right now pallet-scheduler is not putting back postponed tasks into the agenda when the early weight check is failing. This pull request ensures that these tasks are put back into the agenda and are not just "lost".

[bkchr]

/cmd prdoc --audience runtime-dev --bump patch

[github-actions]

Command "prdoc --audience runtime-dev --bump patch" has failed ❌! See logs here

[bkchr]

/cmd prdoc --audience runtime_dev --bump patch

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/13641989048
Failed job name: test-linux-stable

[rockbmb]

I see, so this is what was missing from before: the task would have been taken above, and not put back in the agenda.

[bkchr]

Yes

[gui1117]

The change looks good, but I don't understand another part of the code,

if service_task fails, we put back the task into agenda, even when error is Unavailable.

polkadot-sdk/substrate/frame/scheduler/src/lib.rs

Lines 1254 to 1267 in 5439b5f

	agenda[agenda_index as usize] = match result {
	Err((Unavailable, slot)) => {
	dropped += 1;
	slot
	},
	Err((Overweight, slot)) => {
	postponed += 1;
	slot
	},
	Ok(()) => {
	*executed += 1;
	None
	},
	};

But in service_task we do return some task with error Unavailable when:

• getting the preimage failed
• the execution fails because it is overweight and it is the first task

If any of these case happen, the task will stay forever on the agenda of the block and brick the agenda no?

It feels like it should be dropped instead.