cmd/cue: cmd fails to report errors in task names

[vikstrous2]

What version of CUE are you using (cue version)?

$ cue version
cue version v0.4.1 linux/amd64

Does this issue reproduce with the latest release?

yes

What did you do?

cat > test_tool.cue
package test

import (
	"tool/cli"
)

command: {
	write: task: {
		"\(*"a"|*"b")": cli.Print & {
		  text: "TEST1"
		}
	}
}

cue cmd  write ./...

What did you expect to see?

an error about the disjunction not being valid

What did you see instead?

no output, silent failure

[myitcv]

Confirmed with d4d0f14.

This has overlap with our plans for cuerun insofar as the method of declaring commands might change. Nonetheless, regardless of how commands are specified, we should better surface errors.

[mpvl]

This is independent of the decision about cuerun.