Keep a check build whose key is unchanged instead of building it again

A fresh check asked when only the trunk moved rebuilt every image, though
the reuse key said nothing it is built from changed: a controller check
took about 12 minutes instead of 5.5. The check now keeps a build kept
under its key when a verdict of the build seat names that key and every
digest, names it as the build's own check so a walk takes it, and the
cleanup keeps it while any check names it (novox/hq issue 703).

cmd/mesh-controller/release_plan.go

@@ -386,6 +386,21 @@ var checkedBuildsOf = func(ctx context.Context, pulls []link.PullRef) ([]link.Ch
 	return link.ReadCheckBuilds(ctx, js, buildSeatHeld(ctx), pulls, time.Now().Add(-builder.CheckBuildsKept))
 }
 
+// checkedBuildsOfModules are the builds the build seat's checks of any pull request said they made, or kept, of
+// those modules within the week check builds are kept (novox/hq issue 703): what a check may keep instead of
+// building. A variable so a test needs no bus.
+var checkedBuildsOfModules = func(ctx context.Context, modules []string) ([]link.CheckedBuild, error) {
+	if len(modules) == 0 {
+		return nil, nil
+	}
+	js, err := aBus()
+	if err != nil {
+		return nil, err
+	}
+	defer js.Close()
+	return link.ReadCheckBuildsOf(ctx, js, buildSeatHeld(ctx), modules, time.Now().Add(-builder.CheckBuildsKept))
+}
+
 // reuseWithVerdicts is a walk's leave with the builds its pull requests' verdicts name: the only builds the builder
 // may take (ADR 0350 §2). When they cannot be read the leave names none, and the walk builds, saying why.
 func reuseWithVerdicts(ctx context.Context, r *link.ReuseAsk) *link.ReuseAsk {