mesh-vault starts its passes once Serve holds the runtime's channel: started earlier every watch is refused and waits for the minute's pass (issue 774)

Checked by TestTheVaultWholeRotatesANodesLoginWithAStandInEngine: the race it met is what this closes.

Claude-Session: https://claude.ai/code/session_01NcbgfFSnn24M3GcqttoU7i

modules/mesh-vault/cmd/mesh-vault/main.go

@@ -302,9 +302,20 @@ func readPlanRaw(key string) ([]byte, error) {
 // assignmentKeys is every key of the controller's assignments mirror, read the same way.
 func assignmentKeys() ([]string, error) { return stdio.State(AssignmentsRead).Keys() }
 
+// Checked by TestTheVaultWholeRotatesANodesLoginWithAStandInEngine: the race it met (a pass before Serve, every watch
+// refused, the rotation waiting for the minute's pass) is what this closes.
+// afterServed runs f once served is closed, that is once stdio.Serve holds the runtime's channel: every function of the
+// bus refuses before that ("before Serve"), and a watch refused then waits for the minute's pass.
+func afterServed(served <-chan struct{}, f func()) {
+	go func() {
+		<-served
+		f()
+	}()
+}
+
 func main() {
 	env := build()
-	go func() {
+	afterServed(stdio.Served(), func() {
 		tick := time.NewTicker(time.Minute)
 		defer tick.Stop()
 		// At start, every covered account it holds whose hash is not of its current generation (ADR 0547 clause 9).
@@ -361,7 +372,7 @@ func main() {
 			}
 			<-tick.C
 		}
-	}()
+	})
 	if err := stdio.Serve("", tools(env)); err != nil {
 		say("%v", err)
 		os.Exit(1)