internal/rosa: collection meta-artifact

This is a stub FloodArtifact for concurrently curing multiple artifacts.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/rosa.go

@@ -20,6 +20,9 @@ const (
 
 	// kindBusyboxBin is the kind of [pkg.Artifact] of busyboxBin.
 	kindBusyboxBin
+
+	// kindCollection is the kind of [Collect]. It never cures successfully.
+	kindCollection
 )
 
 // mustDecode is like [pkg.MustDecode], but replaces the zero value and prints
@@ -588,3 +591,29 @@ cd '/usr/src/` + name + `/'
 		})...,
 	)
 }
+
+// Collected is returned by [Collect.Cure] to indicate a successful collection.
+type Collected struct{}
+
+// Error returns a constant string to satisfy error, but should never be seen
+// by the user.
+func (Collected) Error() string { return "artifacts successfully collected" }
+
+// Collect implements [pkg.FloodArtifact] to concurrently cure multiple
+// [pkg.Artifact]. It returns [Collected].
+type Collect []pkg.Artifact
+
+// Cure returns [Collected].
+func (*Collect) Cure(*pkg.FContext) error { return Collected{} }
+
+// Kind returns the hardcoded [pkg.Kind] value.
+func (*Collect) Kind() pkg.Kind { return kindCollection }
+
+// Params does not write anything, dependencies are already represented in the header.
+func (*Collect) Params(*pkg.IContext) {}
+
+// Dependencies returns [Collect] as is.
+func (c *Collect) Dependencies() []pkg.Artifact { return *c }
+
+// IsExclusive returns false: Cure is a noop.
+func (*Collect) IsExclusive() bool { return false }