CAT-D6: distribution's health is a tool the runtime runs outside the program, asking versions through the store's read side

An http probe of /v2/ said only that a port answered; design 51 asks the health check to call versions per seat and
probe the read side each minute, naming the program when it is down, from outside its process. registry_health asks
versions of each seat through the program's port, writes the read-side finding while it fails and clears it after.

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

modules/distribution/cmd/distribution-tools/main.go

@@ -266,6 +266,12 @@ func tools(v *holder.Verbs, windows kept[holder.Window]) []stdio.Tool {
 				ref, err := v.Mirror(holder.ImageSeat, stdio.CallerOf(args), r)
 				return map[string]any{"reference": ref}, err
 			}},
+		stdio.Tool{Name: "registry_health", Description: "distribution's health check, run by the runtime each minute: versions of each seat asked through the store's read side (the program's port 5000); fails naming the program when it does not answer.",
+			Input: obj(map[string]any{}),
+			Run: func(map[string]any) (any, error) {
+				front, _ := url.Parse("http://127.0.0.1:5000")
+				return holder.Health(&holder.OCI{Base: front}, finding)
+			}},
 		stdio.Tool{Name: "registry_incoming", Description: "Open transfers of incoming and its fill; with drop, drops one by hand (a hand act, why required).",
 			Input: obj(map[string]any{"drop": s("a transfer id to drop"), "why": s("why it is dropped")}),
 			Run: func(args map[string]any) (any, error) {