Record the bases a build copies, keep them by the builds that stood on them, and copy each image once

A copied base was named only in what a build stood on, and nowhere when the build failed,
so the store's sweep could never let one go (hq issue 321). One repository per upstream
image stops each module asking the public registry for the same image again, and letting
an index go now takes its own platform manifests, which otherwise kept every byte. A
person can record the copies no record names through the new mirrors verb (hq ADR 0257).

The forge test fix is the same commit as on feat/plain-notifications: main fails without it.

cmd/mesh-controller/seatverbs.go

@@ -605,6 +605,30 @@ func (a *verbArguments) commandLine() ([]string, error) {
 			return nil, err
 		}
 		return []string{"images", str("node"), "--json"}, nil
+	case "mirrors":
+		// novox/hq ADR 0257.
+		argv := []string{"mirrors", "--json"}
+		record := str("record")
+		why := str("why")
+		if record == "" {
+			if on("confirm") || why != "" {
+				return nil, errors.New("mirrors takes confirm and why only with record: there is nothing " +
+					"else it records. Nothing was done")
+			}
+			return argv, nil
+		}
+		argv = append(argv, "--record", record)
+		if !on("confirm") {
+			if why != "" {
+				return nil, errors.New("mirrors takes why only with confirm: without confirm it is a dry run, " +
+					"and a reason for nothing would be recorded nowhere. Nothing was done")
+			}
+			return argv, nil
+		}
+		if err := need("why"); err != nil {
+			return nil, fmt.Errorf("%w: recording a copy as the mesh's is a hand act, which says why. Nothing was done", err)
+		}
+		return append(argv, "--confirm", "--why", why), nil
 	case "data":
 		argv := []string{"data", "--json"}
 		if m := str("machine"); m != "" {
@@ -804,7 +828,7 @@ func (a *verbArguments) commandLine() ([]string, error) {
 var jsonVerbs = map[string]bool{"status": true, "seats": true, "plan": true, "collection": true,
 	"hand-acts": true, "durations": true, "conditions": true, "doctor": true, "retire": true, "cleanup": true, "data": true,
 	// What the records say the registries may keep (novox/hq ADR 0251).
-	"artifacts": true, "collect": true, "images": true,
+	"artifacts": true, "collect": true, "images": true, "mirrors": true,
 	// The delivery's owner's verbs answer JSON where they read (plan, order, check, walks) — novox/hq ADR 0239.
 	"delivery": true}
 
@@ -835,6 +859,8 @@ func repairingCommand(argv []string) string {
 		return "cleanup delete"
 	case argv[0] == "collect" && slices.Contains(argv, "--confirm"):
 		return "collect"
+	case argv[0] == "mirrors" && slices.Contains(argv, "--confirm"):
+		return "mirrors"
 	}
 	return ""
 }