Merge fix/1121-holds-released: delivery 2 on the builds' new layout (issue 1121)

Delivery 2 deleted the move and chain_moved, so the layout of the builds under their modules is made by the controller's start (LayBuildsOut), recorded by the key layout.done in the builds bucket, retried every half minute with an urgent condition while it fails; the chain on the bus is refused until it exists. Its source readers use the module and pointer reads.

cmd/mesh-controller/chain.go

@@ -42,6 +42,9 @@ func attachTheChain(ctx context.Context, inv *inventory.Inventory, server *link.
 		return err
 	}
 	inv.UseChain(c)
+	inv.RequireLayout()
+	// And the builds laid out under their modules, once, before they are read (issue 1121).
+	go layBuildsOutSoon(ctx, inv)
 	// And the requests the move of delivery 1 found never handed over, asked again once (askAgain), once it is serving.
 	go askAgainSoon(ctx, inv)
 	// And what delivery 1 recorded of what each machine was sent, copied onto the keys of the assignments (CopySentBuilds).
@@ -130,3 +133,39 @@ func copySentBuildsSoon(ctx context.Context, inv *inventory.Inventory) {
 
 // chainMoveRetry is how long the copy waits before it tries again.
 const chainMoveRetry = 30 * time.Second
+
+// kindBuildsNotLaidOut is the condition of the layout of the builds under their modules that has not succeeded: until it
+// has, no build is read, and a send that needs one is refused with the reason.
+const kindBuildsNotLaidOut = "builds-not-laid-out"
+
+// layBuildsOutSoon lays the builds out under their modules as soon as this controller holds the lease (the chain refuses a
+// write before), and tries again every half minute while it fails, loudly: each failure is printed, and the first raises an
+// urgent condition until it has worked. It is idempotent (LayBuildsOut).
+func layBuildsOutSoon(ctx context.Context, inv *inventory.Inventory) {
+	failed := false
+	for {
+		err := inv.LayBuildsOut(ctx, func(format string, args ...any) { fmt.Printf("chain: "+format+"\n", args...) })
+		o := conditions.Observation{Scope: conditions.ScopeBuild, ID: kindBuildsNotLaidOut, Token: kindBuildsNotLaidOut,
+			Kind: kindBuildsNotLaidOut, Severity: conditions.Urgent, Resolver: conditions.ResolverOperator,
+			Source: "chain", Summary: "the builds are not laid out under their modules, so none is read: "}
+		if err != nil {
+			fmt.Printf("chain: the builds are not laid out under their modules, and none is read until they are: %v\n", err)
+			if keeper := conditionsFrom; keeper != nil && !failed {
+				o.Summary += err.Error()
+				if _, oerr := keeper.Observe(ctx, o); oerr == nil {
+					failed = true
+				}
+			}
+		} else {
+			if keeper := conditionsFrom; keeper != nil && failed {
+				_, _ = keeper.Clear(ctx, o.Key(), "laid out")
+			}
+			return
+		}
+		select {
+		case <-ctx.Done():
+			return
+		case <-time.After(chainMoveRetry):
+		}
+	}
+}