internal/pkg: exclusive artifacts

This alleviates scheduler overhead when curing many artifacts.

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

internal/pkg/exec.go

@@ -105,6 +105,9 @@ type execArtifact struct {
 	// equivalent to execTimeoutDefault. This value is never encoded in Params
 	// because it cannot affect outcome.
 	timeout time.Duration
+
+	// Caller-supplied exclusivity value, returned as is by IsExclusive.
+	exclusive bool
 }
 
 var _ fmt.Stringer = new(execArtifact)
@@ -123,7 +126,7 @@ var _ KnownChecksum = new(execNetArtifact)
 func (a *execNetArtifact) Checksum() Checksum { return a.checksum }
 
 // Kind returns the hardcoded [Kind] constant.
-func (a *execNetArtifact) Kind() Kind { return KindExecNet }
+func (*execNetArtifact) Kind() Kind { return KindExecNet }
 
 // Params is [Checksum] concatenated with [KindExec] params.
 func (a *execNetArtifact) Params(ctx *IContext) {
@@ -157,13 +160,14 @@ func (a *execNetArtifact) Cure(f *FContext) error {
 // negative timeout value is equivalent tp [ExecTimeoutDefault], a timeout value
 // greater than [ExecTimeoutMax] is equivalent to [ExecTimeoutMax].
 //
-// The user-facing name is not accessible from the container and does not
-// affect curing outcome. Because of this, it is omitted from parameter data
-// for computing identifier.
+// The user-facing name and exclusivity value are not accessible from the
+// container and does not affect curing outcome. Because of this, it is omitted
+// from parameter data for computing identifier.
 func NewExec(
 	name string,
 	checksum *Checksum,
 	timeout time.Duration,
+	exclusive bool,
 
 	dir *check.Absolute,
 	env []string,
@@ -181,7 +185,7 @@ func NewExec(
 	if timeout > ExecTimeoutMax {
 		timeout = ExecTimeoutMax
 	}
-	a := execArtifact{name, paths, dir, env, pathname, args, timeout}
+	a := execArtifact{name, paths, dir, env, pathname, args, timeout, exclusive}
 	if checksum == nil {
 		return &a
 	}
@@ -189,7 +193,7 @@ func NewExec(
 }
 
 // Kind returns the hardcoded [Kind] constant.
-func (a *execArtifact) Kind() Kind { return KindExec }
+func (*execArtifact) Kind() Kind { return KindExec }
 
 // Params writes paths, executable pathname and args.
 func (a *execArtifact) Params(ctx *IContext) {
@@ -237,6 +241,9 @@ func (a *execArtifact) Dependencies() []Artifact {
 	return slices.Concat(artifacts...)
 }
 
+// IsExclusive returns the caller-supplied exclusivity value.
+func (a *execArtifact) IsExclusive() bool { return a.exclusive }
+
 // String returns the caller-supplied reporting name.
 func (a *execArtifact) String() string { return a.name }