@@ -377,20 +377,31 @@ describe("overlayImmutable", () => {
     })
   })
 
-  it("does NOT materialise an immutable leaf when its ancestor is missing in target (pinned current behaviour)", () => {
-    // Tracked in cozystack/cozystack-ui#9.
-    // Defence-in-depth gap: if the YAML editor strips the parent object
-    // entirely, overlay cannot reach the leaf to copy the original value.
-    // Pin behaviour so a future contributor fixing the gap notices the
-    // test and revises it.
+  it("materialises an immutable leaf when its ancestor is missing in target", () => {
+    // A YAML edit that strips the parent object must not strip the immutable
+    // leaf with it. foundationdb's storage.storageClass is a shipped path of
+    // this shape.
     const submitted = { spec: {} } as Record<string, unknown>
     const original = {
-      spec: { backup: { storageClass: "slow" } },
+      spec: { storage: { storageClass: "replicated", size: "10Gi" } },
     }
     const result = overlayImmutable(submitted, original, [
-      ["spec", "backup", "storageClass"],
+      ["spec", "storage", "storageClass"],
+    ])
+    expect(result).toEqual({ spec: { storage: { storageClass: "replicated" } } })
+  })
+
+  it("materialises an immutable leaf when its ancestor is null in target", () => {
+    // `storage:` with nothing under it parses to null, not to a missing key,
+    // so the walker has to treat it the same as absent.
+    const submitted = { spec: { storage: null } } as Record<string, unknown>
+    const original = {
+      spec: { storage: { storageClass: "replicated", size: "10Gi" } },
+    }
+    const result = overlayImmutable(submitted, original, [
+      ["spec", "storage", "storageClass"],
     ])
-    expect(result).toEqual({ spec: {} })
+    expect(result).toEqual({ spec: { storage: { storageClass: "replicated" } } })
   })
 
   it("array reordering by the user with index-aligned overlay re-anchors source values to the new index (pinned current behaviour)", () => {
 
@@ -174,7 +174,11 @@ function overlayPath(
   const sourceVal = sourceObj ? sourceObj[seg] : undefined
   const targetObj = isPlainObject(target)
     ? (target as Record<string, unknown>)
-    : null
+    : // A YAML edit can drop the whole intermediate object; materialise it so
+      // the immutable leaf underneath is still restored from source.
+      sourceVal !== undefined && (target === undefined || target === null)
+      ? {}
+      : null
   if (!targetObj) return target
   if (
     sourceVal === undefined &&