diff --git a/.changeset/action-undoable.md b/.changeset/action-undoable.md
new file mode 100644
index 0000000000..4561fbf88c
--- /dev/null
+++ b/.changeset/action-undoable.md
@@ -0,0 +1,12 @@
+---
+"@objectstack/spec": minor
+---
+
+feat(action): `undoable` flag on the UI Action schema
+
+Single-record update actions can declare `undoable: true`. The runtime captures
+the record's prior field values and offers an "Undo" affordance on the success
+toast (backed by the client UndoManager). Pairs with the objectui runtime that
+honours it. Also documents that conditional `visible` / `disabled` CEL
+predicates are evaluated by the action renderers (used here to hide an action
+when it no longer applies, e.g. Convert Lead on an already-converted lead).
diff --git a/examples/app-crm/src/actions/convert-lead.action.ts b/examples/app-crm/src/actions/convert-lead.action.ts
index e31d1376be..91045a4a81 100644
--- a/examples/app-crm/src/actions/convert-lead.action.ts
+++ b/examples/app-crm/src/actions/convert-lead.action.ts
@@ -16,4 +16,9 @@ export const ConvertLeadAction: UI.Action = {
   target: 'crm_convert_lead_wizard',
   locations: ['list_item', 'record_header', 'record_more'],
   recordIdParam: 'recordId',
+  // Conditional visibility (CEL): hide the action once the lead is already
+  // converted — so the button disappears rather than the user clicking it and
+  // hitting the flow's "already converted" guard screen. The flow keeps that
+  // guard as a server-side backstop.
+  visible: 'record.status != "converted"',
 };
diff --git a/examples/app-crm/src/actions/index.ts b/examples/app-crm/src/actions/index.ts
index 0957b456b8..9490e28e5f 100644
--- a/examples/app-crm/src/actions/index.ts
+++ b/examples/app-crm/src/actions/index.ts
@@ -1,3 +1,4 @@
 // Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
 
 export { ConvertLeadAction } from './convert-lead.action.js';
+export { ParkLeadAction } from './park-lead.action.js';
diff --git a/examples/app-crm/src/actions/park-lead.action.ts b/examples/app-crm/src/actions/park-lead.action.ts
new file mode 100644
index 0000000000..3960c831fd
--- /dev/null
+++ b/examples/app-crm/src/actions/park-lead.action.ts
@@ -0,0 +1,31 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+import type { UI } from '@objectstack/spec';
+
+/**
+ * Row-level action on crm_lead — reassign the lead's owner.
+ *
+ * Demonstrates the `undoable` action affordance: it's a single-record field
+ * update (`assigned_to`), so the runtime captures the prior owner and the
+ * success toast offers an "Undo" that restores it (backed by the client
+ * UndoManager — Ctrl+Z works too). Prompts for the new owner via one param
+ * (pre-filled with "Triage Queue").
+ */
+export const ParkLeadAction: UI.Action = {
+  name: 'crm_park_lead',
+  label: 'Reassign Lead',
+  description: 'Reassign this lead to a new owner (undoable).',
+  icon: 'UserPlus',
+  objectName: 'crm_lead',
+  // `type: 'api'` with a non-URL target routes to the console runtime's generic
+  // `dataSource.update` path (the row id comes from the list_item row record).
+  type: 'api',
+  target: 'crm_lead',
+  // List-row only: the apiHandler needs the row record to capture prior values.
+  locations: ['list_item'],
+  params: [
+    { field: 'assigned_to', label: 'Reassign to', defaultValue: 'Triage Queue', required: true },
+  ],
+  undoable: true,
+  successMessage: 'Lead reassigned.',
+};
diff --git a/packages/spec/src/ui/action.zod.ts b/packages/spec/src/ui/action.zod.ts
index db0cf8345e..d26cd40301 100644
--- a/packages/spec/src/ui/action.zod.ts
+++ b/packages/spec/src/ui/action.zod.ts
@@ -316,6 +316,10 @@ export const ActionSchema = lazySchema(() => z.object({
   // set a friendly failure toast instead of surfacing the raw error string.
   errorMessage: I18nLabelSchema.optional().describe('Error message to show when the action fails (overrides the raw error).'),
   refreshAfter: z.boolean().default(false).describe('Refresh view after execution'),
+  // Single-record update actions only. When true, the runtime captures the
+  // record's prior field values and offers an "Undo" affordance on the success
+  // toast (backed by the client UndoManager) to restore them.
+  undoable: z.boolean().optional().describe('Offer an Undo affordance after this single-record update action succeeds.'),
 
   /**
    * Result Dialog — describe how to render the API response on success.