The first read of a chain not laid out lays it out, so no read of the start is refused (issue 1121)

The layout gate is switched on when the stores open (UseChainOpener), before
attachTheChain; a read of the start came first, was refused, and the
controller exited. A read that finds no marker now lays the builds out once,
under a lock, and is refused only when that fails (a process without the
lease).

internal/inventory/chain.go

@@ -41,6 +41,16 @@ func (i *Inventory) RequireLayout() {
 	i.state.mu.Unlock()
 }
 
+// layingOut lets one read at a time lay the builds out; the others wait for it and then find the marker.
+var layingOut sync.Mutex
+
+// layOutOnce lays the builds out under their modules unless another read did so meanwhile.
+func (i *Inventory) layOutOnce(ctx context.Context) error {
+	layingOut.Lock()
+	defer layingOut.Unlock()
+	return i.LayBuildsOut(ctx, func(format string, args ...any) { fmt.Printf("chain: "+format+"\n", args...) })
+}
+
 func (i *Inventory) markLaidOut() {
 	i.state.mu.Lock()
 	i.state.laid = true
@@ -107,7 +117,13 @@ func (i *Inventory) theChain(ctx context.Context) (*chain.Chain, error) {
 		if _, found, err := c.Builds.GetRaw(ctx, chain.LayoutMarkerKey); err != nil {
 			return nil, err
 		} else if !found {
-			return nil, ErrNotLaidOut
+			// **The first read lays them out** (issue 1121): on 2026-10-18 a read of the controller's start came before
+			// the layout and was refused, and the controller exited and was started again every five seconds. A
+			// process that may write (the lease holder) lays them out here, once; one that may not is refused, loudly.
+			if err := i.layOutOnce(ctx); err != nil {
+				return nil, fmt.Errorf("%w (laying them out now failed: %v)", ErrNotLaidOut, err)
+			}
+			return c, nil
 		}
 		i.markLaidOut()
 	}

internal/inventory/chain_builds_layout_test.go

@@ -3,7 +3,6 @@ package inventory
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"reflect"
 	"sort"
@@ -398,9 +397,10 @@ func TestAnOlderBuildFinishingLastLeavesThePointersOnTheNewer(t *testing.T) {
 	}
 }
 
-// Nothing reads the chain on the bus until the controller's start has laid the builds out and written the marker; the layout
-// is done once.
-func TestTheChainIsRefusedUntilTheBuildsAreLaidOutAndTheLayoutIsDoneOnce(t *testing.T) {
+// Nothing reads the chain on the bus before the builds are laid out and the marker written: the first read of a process that
+// may write lays them out itself (issue 1121: a refused read of the start made the controller exit), and the layout is done
+// once.
+func TestTheFirstReadLaysTheBuildsOutAndTheLayoutIsDoneOnce(t *testing.T) {
 	mem := chain.NewMemory()
 	inv, c := layoutChain(mem)
 	inv.RequireLayout()
@@ -409,11 +409,11 @@ func TestTheChainIsRefusedUntilTheBuildsAreLaidOutAndTheLayoutIsDoneOnce(t *test
 	if _, err := c.Builds.Create(ctx, old.ID, old); err != nil {
 		t.Fatal(err)
 	}
-	if _, err := inv.theChain(ctx); !errors.Is(err, ErrNotLaidOut) {
-		t.Fatalf("a read before the layout answered %v", err)
+	if _, err := inv.theChain(ctx); err != nil {
+		t.Fatalf("the first read was refused, not laid out: %v", err)
 	}
-	if err := inv.LayBuildsOut(ctx, nil); err != nil {
-		t.Fatal(err)
+	if !containsKey(keysOf(t, mem), chain.BuildKey("alpha", old.ID)) {
+		t.Fatalf("the first read did not lay %s out under its module: %v", old.ID, keysOf(t, mem))
 	}
 	if _, err := inv.theChain(ctx); err != nil {
 		t.Fatalf("a read after the layout answered %v", err)

internal/inventory/chain_first_read_lays_out_test.go

@@ -0,0 +1,25 @@
+package inventory
+
+import (
+	"context"
+	"testing"
+
+	"github.com/novox/mesh-controller/internal/chain"
+)
+
+// The first read of a chain that requires the layout lays the builds out itself when it may write, instead of refusing
+// the controller's own start (issue 1121, 2026-10-18: the controller exited every five seconds).
+func TestTheFirstReadOfAChainNotLaidOutLaysItOut(t *testing.T) {
+	ctx := context.Background()
+	inv, c := anInventoryOnTheChain(t)
+	inv.RequireLayout()
+	if _, found, _ := c.Builds.GetRaw(ctx, chain.LayoutMarkerKey); found {
+		t.Fatal("a fresh chain holds the marker already; the test proves nothing")
+	}
+	if _, err := inv.theChain(ctx); err != nil {
+		t.Fatalf("the first read was refused: %v", err)
+	}
+	if _, found, err := c.Builds.GetRaw(ctx, chain.LayoutMarkerKey); err != nil || !found {
+		t.Fatalf("the read did not lay the builds out: found %v, %v", found, err)
+	}
+}