lint

- Move TransactionLedger + types from @excalidraw/element into
  packages/excalidraw/transaction.ts (no external consumers)
- Move commitSyntheticIncrement from App passthrough to Store directly,
  fix didAppStateChange to use Delta.isRightDifferent instead of
  presence-check, and replace isolated increments queue with direct
  scheduleMicroAction + flushMicroActions
- Remove commitSyntheticHistoryEntry from App, expose store and
  createTransaction on AppClassProperties instead
- Replace O(N) deep-copy snapshot in updateScene with shallow map copy
  (element refs are safe — ledger ignores index, the only in-place
  mutated prop, and deep-copies only recorded elements)
- Merge ledger + manager tests into single transaction.test.tsx
- Update dev-docs to reflect new file structure

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dev-docs/docs/codebase/transactions.mdx

@@ -0,0 +1,125 @@
+# Transactions
+
+Transactions let many live scene updates render immediately while still committing a single durable history entry.
+
+Typical use case:
+
+- AI streaming emits many `NEVER` updates for real-time feedback.
+- Those updates advance the live scene and store snapshot, but do not create undo history.
+- A transaction records the intended logical delta separately, then commits one synthetic durable increment at the end.
+
+## Key Files
+
+### `packages/excalidraw/transaction/`
+
+- `transaction.ts`
+  - `Transaction` is the per-tx instance.
+  - `updateScene()` applies live updates with `captureUpdate: NEVER`.
+  - `updateElements()` is a typed partial-patch helper over `updateScene()`.
+  - `commit()` builds synthetic snapshots and commits one durable entry.
+  - `cancel()` ends the tx without committing history.
+- `ledger.ts`
+  - `TransactionLedger` keeps per-element baseline, target, and touched props across tx steps.
+  - `buildSyntheticSnapshots()` reconciles tx intent with the live scene using `live-wins-per-prop`.
+- `undoOverridePlanner.ts`
+  - Tracks tx intermediate values.
+  - Produces undo override candidates for regular user history entries that were recorded while a tx was active.
+- `manager.ts`
+  - Owns tx lifecycle state and active-tx priority.
+  - Injects tx undo markers into durable deltas at record time.
+  - Resolves effective history deltas at undo/redo time.
+- `diff.ts` / `types.ts`
+  - Shared diff helpers and transaction-specific types.
+
+### `packages/element/src/store.ts`
+
+- `store.commitSyntheticIncrement()`
+  - Builds `StoreSnapshot -> StoreChange -> StoreDelta` from logical before/after snapshots.
+  - Commits the synthetic durable increment immediately through an isolated path.
+  - Does not flush unrelated pending micro actions.
+- `StoreDelta.markers`
+  - Carries extra history markers such as `txUndoOverrides`.
+
+### `packages/excalidraw/history.ts`
+
+- `onBeforeRecord()`
+  - Lets the transaction manager attach markers before a durable delta becomes a history entry.
+- `setEffectiveDeltaResolver()`
+  - Lets the transaction manager rewrite a history delta at undo/redo time before it is applied.
+
+## Flow
+
+1. Caller creates a transaction.
+2. `tx.updateScene()` applies live updates with `NEVER`.
+3. The ledger records net element changes; appState intent is accumulated separately.
+4. Regular user durable edits that happen while the tx is active may receive tx undo markers.
+5. `tx.commit()` asks the ledger for logical before/after snapshots and calls `store.commitSyntheticIncrement()`.
+6. Undo/redo later uses the manager's effective-delta resolver to decide whether ended tx markers should patch the baseline of a regular history entry.
+
+Result:
+
+- live rendering stays immediate;
+- one tx still produces one durable history entry;
+- interleaved regular edits can undo back to the correct pre-tx baseline.
+
+## Undo Examples
+
+### Interleaved Regular Edit
+
+1. Baseline: `rect = (x: 0, stroke: black)`
+2. Tx updates it live to `(x: 200, stroke: red)` with `NEVER`
+3. User makes a regular durable edit: `(x: 200, stroke: purple)`
+4. Tx commits; live stays purple
+
+The user history entry was recorded while the tx was active, so its local baseline is `red`.
+If undo later runs after the tx has ended, restoring `red` is wrong: the correct pre-tx baseline is `black`.
+
+To fix this:
+
+- record-time attaches a tx undo marker to the user history entry
+- perform-time checks whether the tx has already ended
+- if ended, the effective delta is patched so undo restores `black` instead of `red`
+
+### Active Tx vs Ended Tx
+
+Using the same example:
+
+- if the user undoes while the tx is still active, the marker stays inactive and undo restores the tx intermediate value (`red`)
+- if the user undoes after the tx has ended, the marker becomes active and undo restores the pre-tx baseline (`black`)
+
+So markers are recorded early, but applied conditionally.
+
+## AppState
+
+Elements use ledger snapshots. AppState does not.
+
+The transaction instead keeps:
+
+- `initialAppState`: observed appState at tx start
+- `accumulatedAppState`: merged caller intent from `tx.updateScene({ appState })`
+
+At commit, the transaction computes the final appState patch and passes it into `store.commitSyntheticIncrement()`.
+
+## Example
+
+```ts
+const tx = app.transactionManager.create();
+
+tx.updateScene({ elements: updatedElementsA });
+tx.updateScene({ elements: updatedElementsB });
+tx.updateElements({
+  elements: [
+    { id: "rect-1", type: "rectangle", updates: { strokeColor: "#f00" } },
+    { id: "rect-2", type: "rectangle", updates: { x: 120 } },
+  ],
+});
+
+tx.commit();
+```
+
+## Notes
+
+- `commit()` and `cancel()` are idempotent.
+- `updateScene()` and `updateElements()` throw after the tx has ended.
+- Conflict handling inside synthetic snapshots is fixed to `live-wins-per-prop`.
+- Multi-tx interleaving is supported through manager-owned lifecycle tracking and active-tx priority.

packages/element/src/store.ts

@@ -111,6 +111,67 @@ export class Store {
     this.scheduleAction(CaptureUpdateAction.IMMEDIATELY);
   }
 
+  /**
+   * Commits a synthetic durable history entry without changing the live scene.
+   *
+   * Builds StoreSnapshot → StoreChange → StoreDelta from the provided
+   * logical before/after element maps and optional appState patches, then
+   * emits the resulting durable increment immediately through an isolated
+   * path that does not flush pending micro actions.
+   *
+   * appState patches are merged on top of the current observed appState
+   * baseline so only the provided keys participate in the synthetic diff.
+   */
+  public commitSyntheticIncrement(params: {
+    logicalBefore: {
+      elements: SceneElementsMap;
+      appState?: Partial<ObservedAppState>;
+    };
+    logicalAfter: {
+      elements: SceneElementsMap;
+      appState?: Partial<ObservedAppState>;
+    };
+  }): boolean {
+    const { logicalBefore, logicalAfter } = params;
+    const observedAppStateBaseline = this.snapshot.appState;
+    const syntheticAppStateBefore = logicalBefore.appState
+      ? { ...observedAppStateBaseline, ...logicalBefore.appState }
+      : observedAppStateBaseline;
+    const syntheticAppStateAfter = logicalAfter.appState
+      ? { ...observedAppStateBaseline, ...logicalAfter.appState }
+      : observedAppStateBaseline;
+    const didAppStateChange = Delta.isRightDifferent(
+      syntheticAppStateBefore,
+      syntheticAppStateAfter,
+    );
+    const prevSnapshot = StoreSnapshot.create(
+      logicalBefore.elements,
+      syntheticAppStateBefore,
+      {
+        didElementsChange: true,
+        didAppStateChange,
+      },
+    );
+    const nextSnapshot = StoreSnapshot.create(
+      logicalAfter.elements,
+      syntheticAppStateAfter,
+      {
+        didElementsChange: true,
+        didAppStateChange,
+      },
+    );
+    const change = StoreChange.create(prevSnapshot, nextSnapshot);
+    const delta = StoreDelta.calculate(prevSnapshot, nextSnapshot);
+
+    if (delta.isEmpty()) {
+      return false;
+    }
+
+    this.emitIsolatedDurableIncrement(change, delta);
+
+    return true;
+  }
+
   /**
    * Schedule special "micro" actions, to-be executed before the next commit, before it executes a scheduled "macro" action.
    */
@@ -206,6 +267,7 @@ export class Store {
   public clear(): void {
     this.snapshot = StoreSnapshot.empty();
     this.scheduledMacroActions = new Set();
+    this.scheduledMicroActions = [];
   }
 
   /**
@@ -245,6 +307,24 @@ export class Store {
     }
   }
 
+  /**
+   * Emits a synthetic durable increment immediately without draining the
+   * regular micro-action queue.
+   */
+  private emitIsolatedDurableIncrement(change: StoreChange, delta: StoreDelta) {
+    const nextSnapshot = this.applyChangeToSnapshot(change);
+
+    if (!nextSnapshot) {
+      return;
+    }
+
+    try {
+      this.emitDurableIncrement(nextSnapshot, change, delta);
+    } finally {
+      this.snapshot = nextSnapshot;
+    }
+  }
+
   /**
    * Performs change calculation and emits an ephemeral increment.
    *
@@ -491,6 +571,89 @@ export class EphemeralIncrement extends StoreIncrement {
   }
 }
 
+/**
+ * Serializable delta marker used to recover pre-tx undo baselines
+ * without rewriting history stack entries.
+ */
+export type TxUndoOverride = {
+  txId: string;
+  elementId: string;
+  prop: string;
+  expectedInsertedValue: unknown;
+  preTxBaselineValue: unknown;
+  consumedKey: string;
+};
+
+export type StoreDeltaMarkers = {
+  txUndoOverrides?: TxUndoOverride[];
+};
+
+const cloneTxUndoOverride = (override: TxUndoOverride): TxUndoOverride => ({
+  ...override,
+});
+
+const cloneStoreDeltaMarkers = (
+  markers: StoreDeltaMarkers | undefined,
+): StoreDeltaMarkers | undefined =>
+  markers
+    ? {
+        ...markers,
+        txUndoOverrides: markers.txUndoOverrides?.map(cloneTxUndoOverride),
+      }
+    : undefined;
+
+const pruneStoreDeltaMarkers = (delta: StoreDelta) => {
+  const txUndoOverrides = delta.markers?.txUndoOverrides;
+  if (!txUndoOverrides || txUndoOverrides.length === 0) {
+    return;
+  }
+
+  const updatedEntries = delta.elements.updated as Record<
+    string,
+    Delta<Record<string, unknown>>
+  >;
+  const nextTxUndoOverrides = txUndoOverrides.filter((override) => {
+    const updatedEntry = updatedEntries[override.elementId];
+    return (
+      !!updatedEntry &&
+      Object.prototype.hasOwnProperty.call(updatedEntry.inserted, override.prop)
+    );
+  });
+
+  if (nextTxUndoOverrides.length === txUndoOverrides.length) {
+    return;
+  }
+
+  if (nextTxUndoOverrides.length === 0) {
+    delta.markers = undefined;
+    return;
+  }
+
+  delta.markers = {
+    ...delta.markers,
+    txUndoOverrides: nextTxUndoOverrides.map(cloneTxUndoOverride),
+  };
+};
+
+export const mergeStoreDeltaMarkers = (
+  delta: StoreDelta,
+  markers: StoreDeltaMarkers,
+) => {
+  const txUndoOverrides = markers.txUndoOverrides ?? [];
+  if (txUndoOverrides.length === 0) {
+    return;
+  }
+
+  const existing = delta.markers?.txUndoOverrides ?? [];
+  delta.markers = {
+    ...delta.markers,
+    txUndoOverrides: [
+      ...existing.map(cloneTxUndoOverride),
+      ...txUndoOverrides.map(cloneTxUndoOverride),
+    ],
+  };
+};
+
 /**
  * Represents a captured delta by the Store.
  */
@@ -499,6 +662,7 @@ export class StoreDelta {
     public readonly id: string,
     public readonly elements: ElementsDelta,
     public readonly appState: AppStateDelta,
+    public markers?: StoreDeltaMarkers,
   ) {}
 
   /**
@@ -508,12 +672,16 @@ export class StoreDelta {
     elements: ElementsDelta,
     appState: AppStateDelta,
     opts: {
-      id: string;
-    } = {
-      id: randomId(),
-    },
+      id?: string;
+      markers?: StoreDeltaMarkers;
+    } = {},
   ) {
-    return new this(opts.id, elements, appState);
+    return new this(
+      opts.id ?? randomId(),
+      elements,
+      appState,
+      cloneStoreDeltaMarkers(opts.markers),
+    );
   }
 
   /**
@@ -538,11 +706,12 @@ export class StoreDelta {
    * Restore a store delta instance from a DTO.
    */
   public static restore(storeDeltaDTO: DTO<StoreDelta>) {
-    const { id, elements, appState } = storeDeltaDTO;
+    const { id, elements, appState, markers } = storeDeltaDTO;
     return new this(
       id,
       ElementsDelta.restore(elements),
       AppStateDelta.restore(appState),
+      cloneStoreDeltaMarkers(markers),
     );
   }
 
@@ -553,11 +722,12 @@ export class StoreDelta {
     id,
     elements: { added, removed, updated },
     appState: { delta: appStateDelta },
+    markers,
   }: DTO<StoreDelta>) {
     const elements = ElementsDelta.create(added, removed, updated);
     const appState = AppStateDelta.create(appStateDelta);
 
-    return new this(id, elements, appState);
+    return new this(id, elements, appState, cloneStoreDeltaMarkers(markers));
   }
 
   /**
@@ -569,8 +739,10 @@ export class StoreDelta {
     for (const delta of deltas) {
       aggregatedDelta.elements.squash(delta.elements);
       aggregatedDelta.appState.squash(delta.appState);
+      mergeStoreDeltaMarkers(aggregatedDelta, delta.markers ?? {});
     }
 
+    pruneStoreDeltaMarkers(aggregatedDelta);
     return aggregatedDelta;
   }
 
@@ -578,7 +750,12 @@ export class StoreDelta {
    * Inverse store delta, creates new instance of `StoreDelta`.
    */
   public static inverse(delta: StoreDelta) {
-    return this.create(delta.elements.inverse(), delta.appState.inverse());
+    const inversed = this.create(
+      delta.elements.inverse(),
+      delta.appState.inverse(),
+      { markers: delta.markers },
+    );
+    return inversed;
   }
 
   /**
@@ -614,7 +791,7 @@ export class StoreDelta {
     nextElements: SceneElementsMap,
     modifierOptions?: "deleted" | "inserted",
   ): StoreDelta {
-    return this.create(
+    const nextDelta = this.create(
       delta.elements.applyLatestChanges(
         prevElements,
         nextElements,
@@ -623,8 +800,11 @@ export class StoreDelta {
       delta.appState,
       {
         id: delta.id,
+        markers: delta.markers,
       },
     );
+    pruneStoreDeltaMarkers(nextDelta);
+    return nextDelta;
   }
 
   public static empty() {

packages/element/tests/store.test.ts

@@ -0,0 +1,140 @@
+import { API } from "@excalidraw/excalidraw/tests/helpers/api";
+
+import { arrayToMap } from "@excalidraw/common";
+
+import type App from "@excalidraw/excalidraw/components/App";
+
+import type { ObservedAppState } from "@excalidraw/excalidraw/types";
+import type {
+  ExcalidrawElement,
+  SceneElementsMap,
+} from "@excalidraw/element/types";
+
+import {
+  CaptureUpdateAction,
+  Store,
+  StoreSnapshot,
+  newElementWith,
+} from "../src";
+
+const getScheduledMicroActionCount = (store: Store) =>
+  (
+    store as unknown as {
+      scheduledMicroActions: Array<() => void>;
+    }
+  ).scheduledMicroActions.length;
+
+const flushMicroActions = (store: Store) => {
+  (
+    store as unknown as {
+      flushMicroActions: () => void;
+    }
+  ).flushMicroActions();
+};
+
+const toSceneElementsMap = (
+  elements: readonly ExcalidrawElement[],
+): SceneElementsMap => arrayToMap(elements) as SceneElementsMap;
+
+const createStoreHarness = (elements: SceneElementsMap) => {
+  const appState: ObservedAppState = StoreSnapshot.empty().appState;
+  const app = {
+    scene: {
+      getElementsMapIncludingDeleted: () => elements,
+    },
+    state: appState,
+  } as unknown as App;
+
+  const store = new Store(app);
+  store.snapshot = StoreSnapshot.create(elements, appState);
+
+  return { store, appState };
+};
+
+describe("Store synthetic increment isolation", () => {
+  it("keeps pending immediate micro actions queued across synthetic commit", () => {
+    const element = API.createElement({
+      type: "rectangle",
+      id: "store-isolated-immediate",
+      x: 0,
+      y: 0,
+    });
+    const baselineElements = toSceneElementsMap([element]);
+    const { store } = createStoreHarness(baselineElements);
+
+    const incrementTypes: Array<"durable" | "ephemeral"> = [];
+    const detach = store.onStoreIncrementEmitter.on((increment) => {
+      incrementTypes.push(increment.type);
+    });
+
+    store.scheduleMicroAction({
+      action: CaptureUpdateAction.IMMEDIATELY,
+      elements: [newElementWith(element, { y: 240 })],
+      appState: undefined,
+    });
+
+    expect(getScheduledMicroActionCount(store)).toBe(1);
+
+    const committed = store.commitSyntheticIncrement({
+      logicalBefore: {
+        elements: baselineElements,
+      },
+      logicalAfter: {
+        elements: toSceneElementsMap([newElementWith(element, { x: 120 })]),
+      },
+    });
+
+    expect(committed).toBe(true);
+    expect(incrementTypes).toEqual(["durable"]);
+    expect(getScheduledMicroActionCount(store)).toBe(1);
+
+    flushMicroActions(store);
+
+    expect(incrementTypes).toEqual(["durable", "durable"]);
+    expect(getScheduledMicroActionCount(store)).toBe(0);
+    detach();
+  });
+
+  it("keeps pending eventually micro actions queued across synthetic commit", () => {
+    const element = API.createElement({
+      type: "rectangle",
+      id: "store-isolated-eventually",
+      x: 0,
+      y: 0,
+    });
+    const baselineElements = toSceneElementsMap([element]);
+    const { store } = createStoreHarness(baselineElements);
+
+    const incrementTypes: Array<"durable" | "ephemeral"> = [];
+    const detach = store.onStoreIncrementEmitter.on((increment) => {
+      incrementTypes.push(increment.type);
+    });
+
+    store.scheduleMicroAction({
+      action: CaptureUpdateAction.EVENTUALLY,
+      elements: [newElementWith(element, { y: 240 })],
+      appState: undefined,
+    });
+
+    expect(getScheduledMicroActionCount(store)).toBe(1);
+
+    const committed = store.commitSyntheticIncrement({
+      logicalBefore: {
+        elements: baselineElements,
+      },
+      logicalAfter: {
+        elements: toSceneElementsMap([newElementWith(element, { x: 120 })]),
+      },
+    });
+
+    expect(committed).toBe(true);
+    expect(incrementTypes).toEqual(["durable"]);
+    expect(getScheduledMicroActionCount(store)).toBe(1);
+
+    flushMicroActions(store);
+
+    expect(incrementTypes).toEqual(["durable", "ephemeral"]);
+    expect(getScheduledMicroActionCount(store)).toBe(0);
+    detach();
+  });
+});

packages/excalidraw/components/App.tsx

@@ -361,6 +361,7 @@ import { restoreAppState, restoreElements } from "../data/restore";
 import { getCenter, getDistance } from "../gesture";
 import { History } from "../history";
 import { defaultLang, getLanguage, languages, setLanguage, t } from "../i18n";
+import { TransactionManager } from "../transaction";
 
 import {
   calculateScrollCenter,
@@ -637,7 +638,8 @@ class App extends React.Component<AppProps, AppState> {
   public library: AppClassProperties["library"];
   public libraryItemsFromStorage: LibraryItems | undefined;
   public id: string;
-  private store: Store;
+  public transactionManager: TransactionManager;
+  public store: Store;
   private history: History;
   public excalidrawContainerValue: {
     container: HTMLDivElement | null;
@@ -832,6 +834,8 @@ class App extends React.Component<AppProps, AppState> {
 
     this.store = new Store(this);
     this.history = new History(this.store);
+    this.transactionManager = new TransactionManager(this);
+    this.transactionManager.attachHistory(this.history);
 
     this.excalidrawContainerValue = {
       container: this.excalidrawContainerRef.current,
@@ -839,7 +843,6 @@ class App extends React.Component<AppProps, AppState> {
     };
 
     this.fonts = new Fonts(this.scene);
-    this.history = new History(this.store);
 
     this.actionManager.registerAll(actions);
     this.actionManager.registerAction(createUndoAction(this.history));
@@ -4602,6 +4605,11 @@ class App extends React.Component<AppProps, AppState> {
     );
   };
 
+  /** Creates a new transaction for batching mutations into a single undo entry. */
+  public createTransaction: TransactionManager["create"] = () => {
+    return this.transactionManager.create();
+  };
+
   public mutateElement = <TElement extends Mutable<ExcalidrawElement>>(
     element: TElement,
     updates: ElementUpdate<TElement>,

packages/excalidraw/history.ts

@@ -87,10 +87,22 @@ export class HistoryChangedEvent {
   ) {}
 }
 
+export type HistoryBeforeRecordListener = (delta: StoreDelta) => void;
+export type HistoryPerformDirection = "undo" | "redo";
+export type HistoryEffectiveDeltaResolverContext = {
+  direction: HistoryPerformDirection;
+};
+export type HistoryEffectiveDeltaResolver = (
+  delta: HistoryDelta,
+  context: HistoryEffectiveDeltaResolverContext,
+) => HistoryDelta;
+
 export class History {
   public readonly onHistoryChangedEmitter = new Emitter<
     [HistoryChangedEvent]
   >();
+  private readonly onBeforeRecordEmitter = new Emitter<[StoreDelta]>();
+  private effectiveDeltaResolver: HistoryEffectiveDeltaResolver | null = null;
 
   public readonly undoStack: HistoryDelta[] = [];
   public readonly redoStack: HistoryDelta[] = [];
@@ -105,6 +117,20 @@ export class History {
 
   constructor(private readonly store: Store) {}
 
+  /**
+   * Registers a hook that runs before a durable delta is converted
+   * into a history entry.
+   */
+  public onBeforeRecord(callback: HistoryBeforeRecordListener) {
+    return this.onBeforeRecordEmitter.on(callback);
+  }
+
+  public setEffectiveDeltaResolver(
+    resolver: HistoryEffectiveDeltaResolver | null,
+  ) {
+    this.effectiveDeltaResolver = resolver;
+  }
+
   public clear() {
     this.undoStack.length = 0;
     this.redoStack.length = 0;
@@ -119,6 +145,8 @@ export class History {
       return;
     }
 
+    this.onBeforeRecordEmitter.trigger(delta);
+
     // construct history entry, so once it's emitted, it's not recorded again
     const historyDelta = HistoryDelta.inverse(delta);
 
@@ -131,15 +159,14 @@ export class History {
       this.redoStack.length = 0;
     }
 
-    this.onHistoryChangedEmitter.trigger(
-      new HistoryChangedEvent(this.isUndoStackEmpty, this.isRedoStackEmpty),
-    );
+    this.emitHistoryChanged();
   }
 
   public undo(elements: SceneElementsMap, appState: AppState) {
     return this.perform(
       elements,
       appState,
+      "undo",
       () => History.pop(this.undoStack),
       (entry: HistoryDelta) => History.push(this.redoStack, entry),
     );
@@ -149,6 +176,7 @@ export class History {
     return this.perform(
       elements,
       appState,
+      "redo",
       () => History.pop(this.redoStack),
       (entry: HistoryDelta) => History.push(this.undoStack, entry),
     );
@@ -157,6 +185,7 @@ export class History {
   private perform(
     elements: SceneElementsMap,
     appState: AppState,
+    direction: HistoryPerformDirection,
     pop: () => HistoryDelta | null,
     push: (entry: HistoryDelta) => void,
   ): [SceneElementsMap, AppState] | void {
@@ -177,9 +206,15 @@ export class History {
 
       // iterate through the history entries in case they result in no visible changes
       while (historyDelta) {
+        // Roundtrip invariant: whichever delta we execute must be the one that
+        // continues through applyLatestChanges -> inverse -> opposite stack.
+        let entryToPush = historyDelta;
         try {
+          const effectiveDelta = this.resolveEffectiveDelta(historyDelta, {
+            direction,
+          });
           [nextElements, nextAppState, containsVisibleChange] =
-            historyDelta.applyTo(nextElements, nextAppState, prevSnapshot);
+            effectiveDelta.applyTo(nextElements, nextAppState, prevSnapshot);
 
           const prevElements = prevSnapshot.elements;
           const nextSnapshot = prevSnapshot.maybeClone(
@@ -190,7 +225,7 @@ export class History {
 
           const change = StoreChange.create(prevSnapshot, nextSnapshot);
           const delta = HistoryDelta.applyLatestChanges(
-            historyDelta,
+            effectiveDelta,
             prevElements,
             nextElements,
           );
@@ -203,12 +238,12 @@ export class History {
               delta,
             });
 
-            historyDelta = delta;
+            entryToPush = delta;
           }
 
           prevSnapshot = nextSnapshot;
         } finally {
-          push(historyDelta);
+          push(entryToPush);
         }
 
         if (containsVisibleChange) {
@@ -222,12 +257,16 @@ export class History {
     } finally {
       // trigger the history change event before returning completely
       // also trigger it just once, no need doing so on each entry
-      this.onHistoryChangedEmitter.trigger(
-        new HistoryChangedEvent(this.isUndoStackEmpty, this.isRedoStackEmpty),
-      );
+      this.emitHistoryChanged();
     }
   }
 
+  private emitHistoryChanged() {
+    this.onHistoryChangedEmitter.trigger(
+      new HistoryChangedEvent(this.isUndoStackEmpty, this.isRedoStackEmpty),
+    );
+  }
+
   private static pop(stack: HistoryDelta[]): HistoryDelta | null {
     if (!stack.length) {
       return null;
@@ -246,4 +285,15 @@ export class History {
     const inversedEntry = HistoryDelta.inverse(entry);
     return stack.push(inversedEntry);
   }
+
+  private resolveEffectiveDelta(
+    delta: HistoryDelta,
+    context: HistoryEffectiveDeltaResolverContext,
+  ): HistoryDelta {
+    if (!this.effectiveDeltaResolver) {
+      return delta;
+    }
+
+    return this.effectiveDeltaResolver(delta, context);
+  }
 }

packages/excalidraw/package.json

@@ -83,13 +83,13 @@
     "@codemirror/language": "^6.0.0",
     "@codemirror/state": "^6.0.0",
     "@codemirror/view": "^6.0.0",
-    "@lezer/highlight": "^1.0.0",
     "@excalidraw/common": "0.18.0",
     "@excalidraw/element": "0.18.0",
     "@excalidraw/laser-pointer": "1.3.1",
     "@excalidraw/math": "0.18.0",
     "@excalidraw/mermaid-to-excalidraw": "2.2.2",
     "@excalidraw/random-username": "1.1.0",
+    "@lezer/highlight": "^1.0.0",
     "browser-fs-access": "0.38.0",
     "canvas-roundrect-polyfill": "0.0.1",
     "clsx": "1.1.1",

packages/excalidraw/tests/test-utils.ts

@@ -449,29 +449,28 @@ const stripProps = (
   }, {} as Record<string, any>);
 
 export const checkpointHistory = (history: History, name: string) => {
-  expect(
-    history.undoStack.map((x) => ({
-      ...x,
-      elements: {
-        ...x.elements,
-        added: stripProps(x.elements.added, ["seed", "versionNonce"]),
-        removed: stripProps(x.elements.removed, ["seed", "versionNonce"]),
-        updated: stripProps(x.elements.updated, ["seed", "versionNonce"]),
-      },
-    })),
-  ).toMatchSnapshot(`[${name}] undo stack`);
+  const normalizeHistoryEntry = (entry: History["undoStack"][number]) => {
+    const { markers, ...rest } = entry;
 
-  expect(
-    history.redoStack.map((x) => ({
-      ...x,
+    return {
+      ...rest,
+      ...(markers ? { markers } : {}),
       elements: {
-        ...x.elements,
-        added: stripProps(x.elements.added, ["seed", "versionNonce"]),
-        removed: stripProps(x.elements.removed, ["seed", "versionNonce"]),
-        updated: stripProps(x.elements.updated, ["seed", "versionNonce"]),
+        ...entry.elements,
+        added: stripProps(entry.elements.added, ["seed", "versionNonce"]),
+        removed: stripProps(entry.elements.removed, ["seed", "versionNonce"]),
+        updated: stripProps(entry.elements.updated, ["seed", "versionNonce"]),
       },
-    })),
-  ).toMatchSnapshot(`[${name}] redo stack`);
+    };
+  };
+
+  expect(history.undoStack.map(normalizeHistoryEntry)).toMatchSnapshot(
+    `[${name}] undo stack`,
+  );
+
+  expect(history.redoStack.map(normalizeHistoryEntry)).toMatchSnapshot(
+    `[${name}] redo stack`,
+  );
 };
 
 /**

packages/excalidraw/transaction/diff.ts

@@ -0,0 +1,289 @@
+import { type StoreDelta } from "@excalidraw/element";
+
+import type { Delta } from "@excalidraw/element";
+
+import type { Mutable } from "@excalidraw/common/utility-types";
+import type {
+  ExcalidrawElement,
+  OrderedExcalidrawElement,
+  SceneElementsMap,
+} from "@excalidraw/element/types";
+
+import type {
+  ElementChange,
+  ElementPropName,
+  TouchedElementProps,
+} from "./types";
+
+const LEDGER_IGNORED_PROPS = new Set([
+  "version",
+  "versionNonce",
+  "seed",
+  "updated",
+  "index",
+]);
+
+export const TX_UNDO_OVERRIDE_IGNORED_PROPS = new Set([
+  "version",
+  "versionNonce",
+  "isDeleted",
+]);
+
+type ElementRecord = Record<string, unknown>;
+export type ElementUpdatedProps = Omit<
+  Partial<OrderedExcalidrawElement>,
+  "id" | "updated" | "seed"
+>;
+export type ElementUpdatedPropName = Extract<keyof ElementUpdatedProps, string>;
+type ElementPropValueMap = ElementUpdatedProps;
+
+export type ElementUpdatedEntry = Delta<ElementPropValueMap>;
+export type ElementUpdatedEntryMap = Record<string, ElementUpdatedEntry>;
+
+const isPlainObject = (value: unknown): value is Record<string, unknown> =>
+  !!value && typeof value === "object" && !Array.isArray(value);
+
+export const getElementProp = <TProp extends ElementPropName>(
+  element: ExcalidrawElement,
+  prop: TProp,
+): ExcalidrawElement[TProp] =>
+  (element as ElementRecord)[prop] as ExcalidrawElement[TProp];
+
+export const setOrderedElementProp = <TProp extends ElementPropName>(
+  element: Mutable<OrderedExcalidrawElement>,
+  prop: TProp,
+  value: OrderedExcalidrawElement[TProp],
+) => {
+  (element as ElementRecord)[prop] = value;
+};
+
+/** Deep equality used by ledger conflict/touched-prop detection. */
+export const isLedgerValueEqual = (left: unknown, right: unknown): boolean => {
+  if (Object.is(left, right)) {
+    return true;
+  }
+
+  if (Array.isArray(left) && Array.isArray(right)) {
+    if (left.length !== right.length) {
+      return false;
+    }
+    for (let index = 0; index < left.length; index += 1) {
+      if (!isLedgerValueEqual(left[index], right[index])) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  if (isPlainObject(left) && isPlainObject(right)) {
+    const leftKeys = Object.keys(left);
+    const rightKeys = Object.keys(right);
+    if (leftKeys.length !== rightKeys.length) {
+      return false;
+    }
+    for (const key of leftKeys) {
+      if (!Object.prototype.hasOwnProperty.call(right, key)) {
+        return false;
+      }
+      if (!isLedgerValueEqual(left[key], right[key])) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  return false;
+};
+
+/** Shallow-copies a scene map. Entries share references with the original. */
+export const shallowCopySceneElements = (
+  elements: ReadonlyMap<string, ExcalidrawElement>,
+): SceneElementsMap => new Map(elements) as SceneElementsMap;
+
+export const createAllTouchedElementProps = (): TouchedElementProps => ({
+  kind: "all",
+});
+
+export const createPartialTouchedElementProps = (
+  props: Iterable<ElementPropName> = [],
+): TouchedElementProps => ({
+  kind: "partial",
+  props: new Set(props),
+});
+
+export const hasTouchedProps = (touchedProps: TouchedElementProps): boolean =>
+  touchedProps.kind === "all" || touchedProps.props.size > 0;
+
+export const touchesWholeElement = (
+  touchedProps: TouchedElementProps,
+): boolean => touchedProps.kind === "all";
+
+export const isPartialTouchedProps = (
+  touchedProps: TouchedElementProps,
+): touchedProps is Extract<TouchedElementProps, { kind: "partial" }> =>
+  touchedProps.kind === "partial";
+
+export const hasTouchedProp = (
+  touchedProps: TouchedElementProps,
+  prop: ElementPropName,
+): boolean => touchedProps.kind === "all" || touchedProps.props.has(prop);
+
+export const mergeTouchedProps = (
+  left: TouchedElementProps,
+  right: TouchedElementProps,
+): TouchedElementProps => {
+  if (left.kind === "all" || right.kind === "all") {
+    return createAllTouchedElementProps();
+  }
+
+  return createPartialTouchedElementProps([...left.props, ...right.props]);
+};
+
+/** Returns changed property names between two element snapshots. */
+export const collectTouchedProps = (
+  before: ExcalidrawElement | null,
+  after: ExcalidrawElement | null,
+): TouchedElementProps => {
+  if (!before || !after) {
+    return createAllTouchedElementProps();
+  }
+
+  const touchedProps = new Set<ElementPropName>();
+  const keys = new Set<ElementPropName>([
+    ...(Object.keys(before) as ElementPropName[]),
+    ...(Object.keys(after) as ElementPropName[]),
+  ]);
+
+  for (const key of keys) {
+    if (LEDGER_IGNORED_PROPS.has(key)) {
+      continue;
+    }
+    if (
+      !isLedgerValueEqual(
+        getElementProp(before, key),
+        getElementProp(after, key),
+      )
+    ) {
+      touchedProps.add(key);
+    }
+  }
+
+  return createPartialTouchedElementProps(touchedProps);
+};
+
+/** Returns ids whose element snapshot changed between two points in time. */
+export const collectChangedElementIds = (
+  before: ReadonlyMap<string, ExcalidrawElement>,
+  after: ReadonlyMap<string, ExcalidrawElement>,
+) => collectElementChanges(before, after).map((change) => change.id);
+
+export const collectElementChanges = (
+  before: ReadonlyMap<string, ExcalidrawElement>,
+  after: ReadonlyMap<string, ExcalidrawElement>,
+): ElementChange[] => {
+  const changes: ElementChange[] = [];
+  const candidateIds = new Set<string>([...before.keys(), ...after.keys()]);
+
+  for (const id of candidateIds) {
+    const beforeElement = before.get(id) ?? null;
+    const afterElement = after.get(id) ?? null;
+    const touchedProps = collectTouchedProps(beforeElement, afterElement);
+    if (!hasTouchedProps(touchedProps)) {
+      continue;
+    }
+
+    changes.push({
+      id,
+      before: beforeElement,
+      after: afterElement,
+      touchedProps,
+    });
+  }
+
+  return changes;
+};
+
+export const serializeConsumedPropKey = (
+  elementId: string,
+  prop: ElementPropName,
+) => `${elementId}\u0000${prop}`;
+
+export const getUpdatedElementEntries = (delta: StoreDelta) =>
+  delta.elements.updated as ElementUpdatedEntryMap;
+
+export const getElementPropEntries = (props: ElementPropValueMap) =>
+  Object.entries(props) as [
+    ElementUpdatedPropName,
+    ElementUpdatedProps[ElementUpdatedPropName],
+  ][];
+
+export const hasUpdatedElementEntries = (delta: StoreDelta) =>
+  Object.keys(getUpdatedElementEntries(delta)).length > 0;
+
+export const serializeIntermediateValue = (value: unknown): string => {
+  const serialize = (input: unknown, seen: WeakSet<object>): string => {
+    if (input === null) {
+      return "null";
+    }
+
+    switch (typeof input) {
+      case "undefined":
+        return "undefined";
+      case "boolean":
+        return input ? "boolean:true" : "boolean:false";
+      case "number":
+        if (Number.isNaN(input)) {
+          return "number:NaN";
+        }
+        if (Object.is(input, -0)) {
+          return "number:-0";
+        }
+        return `number:${input}`;
+      case "bigint":
+        return `bigint:${input.toString()}`;
+      case "string":
+        return `string:${JSON.stringify(input)}`;
+      case "symbol":
+        return `symbol:${String(input)}`;
+      case "function":
+        return `function:${input.name}`;
+      case "object":
+        break;
+      default:
+        return `unknown:${String(input)}`;
+    }
+
+    if (Array.isArray(input)) {
+      if (seen.has(input)) {
+        return "[CircularArray]";
+      }
+      seen.add(input);
+      const serialized = `[${input
+        .map((item) => serialize(item, seen))
+        .join(",")}]`;
+      seen.delete(input);
+      return serialized;
+    }
+
+    if (isPlainObject(input)) {
+      if (seen.has(input)) {
+        return "{CircularObject}";
+      }
+      seen.add(input);
+      const serialized = `{${Object.keys(input)
+        .sort()
+        .map((key) => `${JSON.stringify(key)}:${serialize(input[key], seen)}`)
+        .join(",")}}`;
+      seen.delete(input);
+      return serialized;
+    }
+
+    try {
+      return `object:${JSON.stringify(input)}`;
+    } catch {
+      return `object:${Object.prototype.toString.call(input)}`;
+    }
+  };
+
+  return serialize(value, new WeakSet<object>());
+};

packages/excalidraw/transaction/index.ts

@@ -0,0 +1,13 @@
+export { collectChangedElementIds } from "./diff";
+export { TransactionLedger } from "./ledger";
+export { Transaction } from "./transaction";
+export { TransactionManager } from "./manager";
+
+export type {
+  AppStateResolver,
+  AppStateResolverContext,
+  TransactionElementUpdate,
+  TransactionLedgerEntry,
+  TransactionStatus,
+  TransactionSummary,
+} from "./types";

packages/excalidraw/transaction/ledger.ts

@@ -0,0 +1,333 @@
+import { deepCopyElement } from "@excalidraw/element";
+
+import type { Mutable } from "@excalidraw/common/utility-types";
+import type {
+  ExcalidrawElement,
+  OrderedExcalidrawElement,
+  SceneElementsMap,
+} from "@excalidraw/element/types";
+
+import {
+  collectElementChanges,
+  collectTouchedProps,
+  getElementProp,
+  hasTouchedProps,
+  isLedgerValueEqual,
+  mergeTouchedProps,
+  setOrderedElementProp,
+  shallowCopySceneElements,
+  touchesWholeElement,
+} from "./diff";
+
+import type { TransactionLedgerEntry } from "./types";
+
+/**
+ * Keeps transaction-level scene mutations and materializes synthetic snapshots
+ * for a single durable history commit.
+ */
+export class TransactionLedger {
+  private readonly entries = new Map<string, TransactionLedgerEntry>();
+
+  /** Whether the transaction has any net element mutations. */
+  hasEntries() {
+    return this.entries.size > 0;
+  }
+
+  /** Returns the ledger entry for an element, if any. */
+  getEntry(elementId: string): TransactionLedgerEntry | undefined {
+    return this.entries.get(elementId);
+  }
+
+  /** Releases all ledger entries. */
+  clear() {
+    this.entries.clear();
+  }
+
+  /** Records one element mutation step into the ledger. */
+  recordStep(
+    before: ReadonlyMap<string, ExcalidrawElement>,
+    after: ReadonlyMap<string, ExcalidrawElement>,
+  ) {
+    for (const change of collectElementChanges(before, after)) {
+      const {
+        id: elementId,
+        before: beforeElement,
+        after: afterElement,
+        touchedProps,
+      } = change;
+
+      const existing = this.entries.get(elementId);
+      if (!existing) {
+        this.entries.set(elementId, {
+          baselineElement: beforeElement
+            ? deepCopyElement(beforeElement)
+            : null,
+          targetElement: afterElement ? deepCopyElement(afterElement) : null,
+          touchedProps,
+        });
+        continue;
+      }
+
+      existing.targetElement = afterElement
+        ? deepCopyElement(afterElement)
+        : null;
+      existing.touchedProps = mergeTouchedProps(
+        existing.touchedProps,
+        touchedProps,
+      );
+
+      // Created then deleted inside one transaction leaves no durable footprint.
+      if (!existing.baselineElement && !existing.targetElement) {
+        this.entries.delete(elementId);
+        continue;
+      }
+      if (!existing.baselineElement && existing.targetElement?.isDeleted) {
+        this.entries.delete(elementId);
+      }
+    }
+  }
+
+  /**
+   * Builds synthetic element before/after snapshots with a fixed
+   * "live-wins-per-prop" strategy.
+   */
+  buildSyntheticSnapshots(live: ReadonlyMap<string, ExcalidrawElement>) {
+    // Shallow copy — untouched elements stay as live references.
+    // Only elements mutated in-place (prop-level updates) are deep-copied below.
+    const elementsBefore = shallowCopySceneElements(live);
+    const elementsAfter = shallowCopySceneElements(live);
+
+    for (const [elementId, entry] of this.entries) {
+      this.reconcileEntrySnapshots(
+        elementId,
+        entry,
+        live,
+        elementsBefore,
+        elementsAfter,
+      );
+    }
+
+    return { elementsBefore, elementsAfter };
+  }
+
+  private reconcileEntrySnapshots(
+    elementId: string,
+    entry: TransactionLedgerEntry,
+    live: ReadonlyMap<string, ExcalidrawElement>,
+    elementsBefore: SceneElementsMap,
+    elementsAfter: SceneElementsMap,
+  ) {
+    if (!entry.baselineElement) {
+      this.applyCreatedElementSnapshots(
+        elementId,
+        entry.targetElement,
+        live,
+        elementsBefore,
+        elementsAfter,
+      );
+      return;
+    }
+
+    if (!entry.targetElement) {
+      this.applyDeletedElementSnapshots(
+        elementId,
+        entry.baselineElement,
+        live,
+        elementsBefore,
+        elementsAfter,
+      );
+      return;
+    }
+
+    this.applyUpdatedElementSnapshots(
+      elementId,
+      entry,
+      live,
+      elementsBefore,
+      elementsAfter,
+    );
+  }
+
+  private applyCreatedElementSnapshots(
+    elementId: string,
+    targetElement: ExcalidrawElement | null,
+    live: ReadonlyMap<string, ExcalidrawElement>,
+    elementsBefore: SceneElementsMap,
+    elementsAfter: SceneElementsMap,
+  ) {
+    if (!targetElement) {
+      return;
+    }
+
+    const liveElement = live.get(elementId) ?? null;
+    if (
+      !liveElement ||
+      liveElement.isDeleted ||
+      hasTouchedProps(collectTouchedProps(targetElement, liveElement))
+    ) {
+      return;
+    }
+
+    elementsBefore.delete(elementId);
+    elementsAfter.set(
+      elementId,
+      deepCopyElement(targetElement) as OrderedExcalidrawElement,
+    );
+  }
+
+  private applyDeletedElementSnapshots(
+    elementId: string,
+    baselineElement: ExcalidrawElement,
+    live: ReadonlyMap<string, ExcalidrawElement>,
+    elementsBefore: SceneElementsMap,
+    elementsAfter: SceneElementsMap,
+  ) {
+    const liveElement = live.get(elementId) ?? null;
+    if (liveElement && !liveElement.isDeleted) {
+      return;
+    }
+
+    elementsBefore.set(
+      elementId,
+      deepCopyElement(baselineElement) as OrderedExcalidrawElement,
+    );
+    elementsAfter.delete(elementId);
+  }
+
+  private applyUpdatedElementSnapshots(
+    elementId: string,
+    entry: TransactionLedgerEntry,
+    live: ReadonlyMap<string, ExcalidrawElement>,
+    elementsBefore: SceneElementsMap,
+    elementsAfter: SceneElementsMap,
+  ) {
+    const liveElement = live.get(elementId) ?? null;
+    const targetElement = entry.targetElement;
+    const baselineElement = entry.baselineElement;
+    const beforeElement = elementsBefore.get(elementId);
+    const afterElement = elementsAfter.get(elementId);
+
+    if (
+      !liveElement ||
+      !baselineElement ||
+      !targetElement ||
+      !beforeElement ||
+      !afterElement
+    ) {
+      return;
+    }
+
+    if (touchesWholeElement(entry.touchedProps)) {
+      this.applyWholeElementSnapshots(
+        elementId,
+        baselineElement,
+        targetElement,
+        liveElement,
+        elementsBefore,
+        elementsAfter,
+      );
+      return;
+    }
+
+    this.applyPerPropSnapshots({
+      entry,
+      liveElement,
+      baselineElement,
+      targetElement,
+      beforeElement,
+      afterElement,
+      elementId,
+      elementsBefore,
+      elementsAfter,
+    });
+  }
+
+  private applyWholeElementSnapshots(
+    elementId: string,
+    baselineElement: ExcalidrawElement,
+    targetElement: ExcalidrawElement,
+    liveElement: ExcalidrawElement,
+    elementsBefore: SceneElementsMap,
+    elementsAfter: SceneElementsMap,
+  ) {
+    const hasLiveConflict = hasTouchedProps(
+      collectTouchedProps(targetElement, liveElement),
+    );
+    if (hasLiveConflict) {
+      return;
+    }
+
+    elementsBefore.set(
+      elementId,
+      deepCopyElement(baselineElement) as OrderedExcalidrawElement,
+    );
+    elementsAfter.set(
+      elementId,
+      deepCopyElement(targetElement) as OrderedExcalidrawElement,
+    );
+  }
+
+  private applyPerPropSnapshots(args: {
+    entry: TransactionLedgerEntry;
+    liveElement: ExcalidrawElement;
+    baselineElement: ExcalidrawElement;
+    targetElement: ExcalidrawElement;
+    beforeElement: ExcalidrawElement;
+    afterElement: ExcalidrawElement;
+    elementId: string;
+    elementsBefore: SceneElementsMap;
+    elementsAfter: SceneElementsMap;
+  }) {
+    const {
+      entry,
+      liveElement,
+      baselineElement,
+      targetElement,
+      beforeElement,
+      afterElement,
+      elementId,
+      elementsBefore,
+      elementsAfter,
+    } = args;
+
+    // Deep-copy before mutating so we never touch live elements.
+    const mutableBefore = deepCopyElement(
+      beforeElement,
+    ) as Mutable<OrderedExcalidrawElement>;
+    const mutableAfter = deepCopyElement(
+      afterElement,
+    ) as Mutable<OrderedExcalidrawElement>;
+    elementsBefore.set(elementId, mutableBefore as OrderedExcalidrawElement);
+    elementsAfter.set(elementId, mutableAfter as OrderedExcalidrawElement);
+
+    if (entry.touchedProps.kind !== "partial") {
+      return;
+    }
+
+    let appliedProps = 0;
+    for (const prop of entry.touchedProps.props) {
+      const liveValue = getElementProp(liveElement, prop);
+      const targetValue = getElementProp(targetElement, prop);
+      if (!isLedgerValueEqual(liveValue, targetValue)) {
+        continue;
+      }
+
+      setOrderedElementProp(
+        mutableBefore,
+        prop,
+        getElementProp(baselineElement, prop),
+      );
+      setOrderedElementProp(mutableAfter, prop, targetValue);
+      appliedProps += 1;
+    }
+
+    if (appliedProps === 0) {
+      return;
+    }
+
+    mutableBefore.version = baselineElement.version;
+    mutableBefore.versionNonce = baselineElement.versionNonce;
+    mutableAfter.version = targetElement.version;
+    mutableAfter.versionNonce = targetElement.versionNonce;
+  }
+}

packages/excalidraw/transaction/manager.ts

@@ -0,0 +1,291 @@
+import {
+  Delta,
+  ElementsDelta,
+  mergeStoreDeltaMarkers,
+  type StoreDelta,
+  type TxUndoOverride,
+} from "@excalidraw/element";
+
+import type { Mutable } from "@excalidraw/common/utility-types";
+
+import {
+  HistoryDelta,
+  type HistoryBeforeRecordListener,
+  type HistoryEffectiveDeltaResolverContext,
+} from "../history";
+
+import {
+  type ElementUpdatedPropName,
+  getUpdatedElementEntries,
+  hasUpdatedElementEntries,
+  isLedgerValueEqual,
+  type ElementUpdatedProps,
+  type ElementUpdatedEntryMap,
+} from "./diff";
+import { Transaction } from "./transaction";
+
+import type { AppClassProperties } from "../types";
+import type { TransactionStatus } from "./types";
+
+type TransactionRecord = {
+  tx: Transaction | null;
+  phase: TransactionStatus;
+};
+type TransactionHistoryBridge = {
+  onBeforeRecord: (callback: HistoryBeforeRecordListener) => () => void;
+  setEffectiveDeltaResolver: (
+    resolver:
+      | ((
+          delta: HistoryDelta,
+          context: HistoryEffectiveDeltaResolverContext,
+        ) => HistoryDelta)
+      | null,
+  ) => void;
+};
+
+type MutableElementUpdatedProps = Mutable<ElementUpdatedProps>;
+
+const setElementUpdatedOverride = (
+  overrides: MutableElementUpdatedProps,
+  prop: ElementUpdatedPropName,
+  value: unknown,
+) => {
+  (overrides as Record<ElementUpdatedPropName, unknown>)[prop] = value;
+};
+
+/**
+ * Thin factory that holds the app reference and creates Transaction instances.
+ */
+export class TransactionManager {
+  private readonly app: AppClassProperties;
+  /**
+   * Single authoritative lifecycle registry for transactions.
+   *
+   * We retain ended/canceled metadata after the tx object is released because
+   * history markers only persist `txId`; undo/redo still needs to resolve
+   * whether a tx was active or already ended when applying effective deltas.
+   */
+  private readonly transactionRecords = new Map<string, TransactionRecord>();
+  /**
+   * Active transaction ids ordered by most-recent registration first.
+   * This preserves deterministic priority when multiple active txs overlap on
+   * the same element+prop and compete to reserve override markers.
+   */
+  private readonly activeTransactionIdsByPriority: string[] = [];
+  private detachBeforeRecordHook: (() => void) | null = null;
+
+  constructor(app: AppClassProperties) {
+    this.app = app;
+  }
+
+  /**
+   * Binds transaction bookkeeping to history lifecycle hooks.
+   * Call once during app initialization.
+   */
+  attachHistory(history: TransactionHistoryBridge) {
+    this.detachBeforeRecordHook?.();
+    history.setEffectiveDeltaResolver((delta, context) =>
+      this.resolveEffectiveDelta(delta, context),
+    );
+    this.detachBeforeRecordHook = history.onBeforeRecord((delta) =>
+      this.onDurableIncrement(delta),
+    );
+  }
+
+  private removeActiveTransactionId(txId: string) {
+    const txIndex = this.activeTransactionIdsByPriority.indexOf(txId);
+    if (txIndex >= 0) {
+      this.activeTransactionIdsByPriority.splice(txIndex, 1);
+    }
+  }
+
+  private getRequiredTransactionRecord(txId: string): TransactionRecord {
+    const record = this.transactionRecords.get(txId);
+    if (!record) {
+      throw new Error(`Unknown transaction: ${txId}`);
+    }
+
+    return record;
+  }
+
+  registerTransaction(tx: Transaction) {
+    this.transactionRecords.set(tx.id, {
+      tx,
+      phase: "active",
+    });
+    this.activeTransactionIdsByPriority.unshift(tx.id);
+  }
+
+  detachTransactionInstance(txId: string) {
+    const record = this.getRequiredTransactionRecord(txId);
+    record.tx = null;
+    this.removeActiveTransactionId(txId);
+  }
+
+  getStatus(txId: string): TransactionStatus {
+    return this.getRequiredTransactionRecord(txId).phase;
+  }
+
+  private markTransactionFinished(
+    txId: string,
+    phase: Exclude<TransactionStatus, "active">,
+  ): TransactionStatus {
+    const record = this.getRequiredTransactionRecord(txId);
+    if (record.phase !== "active") {
+      return record.phase;
+    }
+
+    record.phase = phase;
+    this.removeActiveTransactionId(txId);
+    return record.phase;
+  }
+
+  markTransactionCommitted(txId: string): TransactionStatus {
+    return this.markTransactionFinished(txId, "committed");
+  }
+
+  markTransactionCanceled(txId: string): TransactionStatus {
+    return this.markTransactionFinished(txId, "canceled");
+  }
+
+  onDurableIncrement(delta: StoreDelta) {
+    if (this.activeTransactionIdsByPriority.length === 0) {
+      return;
+    }
+    if (!hasUpdatedElementEntries(delta)) {
+      return;
+    }
+
+    const txUndoOverrides = this.collectUndoOverrides(delta);
+    if (txUndoOverrides.length === 0) {
+      return;
+    }
+
+    mergeStoreDeltaMarkers(delta, { txUndoOverrides });
+  }
+
+  private collectUndoOverrides(delta: StoreDelta): TxUndoOverride[] {
+    const overrides: TxUndoOverride[] = [];
+    const reservedConsumedKeys = new Set<string>();
+
+    for (const txId of this.activeTransactionIdsByPriority) {
+      const record = this.transactionRecords.get(txId);
+      if (!record || record.phase !== "active" || !record.tx) {
+        continue;
+      }
+
+      const txOverrides = record.tx.collectUndoOverridesForDelta(
+        delta,
+        reservedConsumedKeys,
+      );
+
+      for (const override of txOverrides) {
+        if (reservedConsumedKeys.has(override.consumedKey)) {
+          continue;
+        }
+
+        reservedConsumedKeys.add(override.consumedKey);
+        overrides.push(override);
+      }
+    }
+
+    return overrides;
+  }
+
+  private resolveEffectiveDelta(
+    delta: HistoryDelta,
+    _context: HistoryEffectiveDeltaResolverContext,
+  ): HistoryDelta {
+    const txUndoOverrides = delta.markers?.txUndoOverrides;
+    if (!txUndoOverrides || txUndoOverrides.length === 0) {
+      return delta;
+    }
+
+    const updatedEntries = getUpdatedElementEntries(delta);
+    const insertedOverridesByElement = new Map<
+      string,
+      MutableElementUpdatedProps
+    >();
+
+    for (const override of txUndoOverrides) {
+      if (!this.shouldApplyUndoOverride(override.txId)) {
+        continue;
+      }
+
+      const currentEntry = updatedEntries[override.elementId];
+      if (!currentEntry) {
+        continue;
+      }
+
+      const prop = override.prop as ElementUpdatedPropName;
+      const currentInsertedValue = currentEntry.inserted[prop];
+      if (
+        !isLedgerValueEqual(
+          currentInsertedValue,
+          override.expectedInsertedValue,
+        )
+      ) {
+        // Guard against over-applying once the delta has already evolved.
+        continue;
+      }
+
+      const elementOverrides = insertedOverridesByElement.get(
+        override.elementId,
+      );
+      if (elementOverrides) {
+        setElementUpdatedOverride(
+          elementOverrides,
+          prop,
+          override.preTxBaselineValue,
+        );
+      } else {
+        const nextOverrides: MutableElementUpdatedProps = {};
+        setElementUpdatedOverride(
+          nextOverrides,
+          prop,
+          override.preTxBaselineValue,
+        );
+        insertedOverridesByElement.set(override.elementId, nextOverrides);
+      }
+    }
+
+    if (insertedOverridesByElement.size === 0) {
+      return delta;
+    }
+
+    const nextUpdatedEntries: ElementUpdatedEntryMap = {
+      ...updatedEntries,
+    };
+    for (const [elementId, insertedOverrides] of insertedOverridesByElement) {
+      const currentEntry = updatedEntries[elementId];
+      if (!currentEntry) {
+        continue;
+      }
+
+      nextUpdatedEntries[elementId] = Delta.create(
+        { ...currentEntry.deleted },
+        { ...currentEntry.inserted, ...insertedOverrides },
+      );
+    }
+
+    const effectiveElements = ElementsDelta.create(
+      delta.elements.added,
+      delta.elements.removed,
+      nextUpdatedEntries,
+    );
+
+    return HistoryDelta.create(effectiveElements, delta.appState, {
+      id: delta.id,
+      markers: delta.markers,
+    }) as HistoryDelta;
+  }
+
+  private shouldApplyUndoOverride(txId: string): boolean {
+    const record = this.transactionRecords.get(txId);
+    return !!record && record.phase !== "active";
+  }
+
+  create(): Transaction {
+    return new Transaction(this.app, this);
+  }
+}

packages/excalidraw/transaction/transaction.ts

@@ -0,0 +1,286 @@
+import { randomId } from "@excalidraw/common";
+import {
+  CaptureUpdateAction,
+  newElementWith,
+  type ElementUpdate,
+  type StoreDelta,
+  type TxUndoOverride,
+} from "@excalidraw/element";
+
+import { shallowCopySceneElements } from "./diff";
+import { TransactionLedger } from "./ledger";
+
+import {
+  type AppStateResolver,
+  type AppStateResolverContext,
+  type TransactionElementOfType,
+  type TransactionElementUpdate,
+  type TransactionStatus,
+  type TransactionSummary,
+} from "./types";
+import { TxUndoOverridePlanner } from "./undoOverridePlanner";
+
+import type { TransactionManager } from "./manager";
+import type {
+  AppClassProperties,
+  AppState,
+  ObservedAppState,
+  SceneData,
+} from "../types";
+
+type CommitOptions = {
+  resolveAppState?: AppStateResolver;
+};
+
+/**
+ * A transaction that records mutations via `updateScene(NEVER)` and commits
+ * a single synthetic durable history entry at the end.
+ */
+export class Transaction {
+  public readonly id = `tx-${randomId()}`;
+
+  private readonly app: AppClassProperties;
+  private readonly manager: TransactionManager;
+  private readonly ledger = new TransactionLedger();
+  private readonly undoOverridePlanner = new TxUndoOverridePlanner();
+  private readonly initialAppState: Partial<ObservedAppState>;
+
+  private accumulatedAppState: Record<string, unknown> = {};
+  private cachedSummary: TransactionSummary | null = null;
+
+  constructor(app: AppClassProperties, manager: TransactionManager) {
+    this.app = app;
+    this.manager = manager;
+    this.initialAppState = { ...app.store.snapshot.appState };
+    this.manager.registerTransaction(this);
+  }
+
+  get status(): TransactionStatus {
+    return this.manager.getStatus(this.id);
+  }
+
+  private assertActive(action: string): void {
+    const status = this.status;
+    if (status !== "active") {
+      throw new Error(
+        `Cannot ${action} — transaction ${this.id} is already ${status}.`,
+      );
+    }
+  }
+
+  private closeTransaction() {
+    this.manager.detachTransactionInstance(this.id);
+    this.undoOverridePlanner.clear();
+  }
+
+  public collectUndoOverridesForDelta(
+    delta: StoreDelta,
+    reservedConsumedKeys: Set<string>,
+  ): TxUndoOverride[] {
+    if (this.status !== "active") {
+      return [];
+    }
+
+    const candidates =
+      this.undoOverridePlanner.collectCandidatesForDurableDelta(
+        delta,
+        (elementId) => this.ledger.getEntry(elementId),
+        reservedConsumedKeys,
+      );
+
+    if (candidates.length === 0) {
+      return [];
+    }
+
+    const overrides: TxUndoOverride[] = [];
+    for (const candidate of candidates) {
+      this.undoOverridePlanner.markConsumed(candidate.consumedKey);
+      overrides.push({
+        txId: this.id,
+        ...candidate,
+      });
+    }
+
+    return overrides;
+  }
+
+  updateScene<K extends keyof AppState>(data: {
+    elements?: SceneData["elements"];
+    appState?: Pick<AppState, K> | null;
+  }): void {
+    this.assertActive("updateScene");
+
+    // Snapshot before (shallow copy — replaceAllElements mutates the map in-place)
+    const before = shallowCopySceneElements(
+      this.app.scene.getElementsMapIncludingDeleted(),
+    );
+
+    // Apply through the real updateScene with NEVER.
+    this.app.api.updateScene({
+      elements: data.elements,
+      appState: data.appState,
+      captureUpdate: CaptureUpdateAction.NEVER,
+    });
+
+    // Snapshot after
+    const after = this.app.scene.getElementsMapIncludingDeleted();
+
+    this.undoOverridePlanner.recordStep(before, after);
+
+    // Record element diff into ledger
+    this.ledger.recordStep(before, after);
+
+    // Accumulate appState intent
+    if (data.appState) {
+      this.accumulatedAppState = {
+        ...this.accumulatedAppState,
+        ...(data.appState as Record<string, unknown>),
+      };
+    }
+  }
+
+  /**
+   * Partial element updates convenience API.
+   *
+   * Example:
+   * tx.updateElements({
+   *   elements: [
+   *     { id: "a", type: "rectangle", updates: { strokeColor: "#f00" } },
+   *     { id: "b", type: "rectangle", updates: { x: 10, y: 20 } },
+   *   ],
+   * })
+   */
+  updateElements<K extends keyof AppState>(data: {
+    elements: readonly TransactionElementUpdate[];
+    appState?: Pick<AppState, K> | null;
+  }): void {
+    const updatesById = new Map<string, TransactionElementUpdate>();
+
+    for (const update of data.elements) {
+      updatesById.set(update.id, update);
+    }
+
+    if (updatesById.size === 0) {
+      this.updateScene({ appState: data.appState });
+      return;
+    }
+
+    const nextElements = this.app.scene
+      .getElementsIncludingDeleted()
+      .map((element) => {
+        const update = updatesById.get(element.id);
+        if (!update) {
+          return element;
+        }
+        if (element.type !== update.type) {
+          throw new Error(
+            `Cannot apply tx.updateElements update for "${update.id}": expected "${update.type}", got "${element.type}".`,
+          );
+        }
+
+        type MatchingElement = TransactionElementOfType<typeof update.type>;
+        return newElementWith(
+          element as MatchingElement,
+          update.updates as ElementUpdate<MatchingElement>,
+        );
+      });
+
+    this.updateScene({
+      elements: nextElements,
+      appState: data.appState,
+    });
+  }
+
+  commit(options?: CommitOptions): TransactionSummary {
+    if (this.cachedSummary) {
+      return this.cachedSummary;
+    }
+
+    this.manager.markTransactionCommitted(this.id);
+    let historyCommitted = false;
+    try {
+      historyCommitted = this.hasPendingWork()
+        ? this.commitHistoryEntry(options)
+        : false;
+    } finally {
+      this.closeTransaction();
+    }
+
+    const status = this.status;
+    this.cachedSummary = {
+      id: this.id,
+      status,
+      historyCommitted,
+    };
+    this.ledger.clear();
+    return this.cachedSummary;
+  }
+
+  private hasPendingWork() {
+    return this.ledger.hasEntries() || this.hasAccumulatedAppStateIntent();
+  }
+
+  private hasAccumulatedAppStateIntent() {
+    return Object.keys(this.accumulatedAppState).length > 0;
+  }
+
+  private commitHistoryEntry(options?: CommitOptions) {
+    const liveMap = this.app.scene.getElementsMapIncludingDeleted();
+    const { elementsBefore, elementsAfter } =
+      this.ledger.buildSyntheticSnapshots(liveMap);
+
+    const appStateDelta = this.resolveCommitAppStateDelta(options);
+
+    return this.app.store.commitSyntheticIncrement({
+      logicalBefore: { elements: elementsBefore },
+      logicalAfter: {
+        elements: elementsAfter,
+        appState: appStateDelta,
+      },
+    });
+  }
+
+  private resolveCommitAppStateDelta(
+    options?: CommitOptions,
+  ): Partial<ObservedAppState> | undefined {
+    if (!this.hasAccumulatedAppStateIntent()) {
+      return undefined;
+    }
+
+    if (!options?.resolveAppState) {
+      return this.accumulatedAppState as Partial<ObservedAppState>;
+    }
+
+    const context: AppStateResolverContext = {
+      initial: this.initialAppState,
+      accumulated: this.accumulatedAppState as Partial<ObservedAppState>,
+      live: { ...this.app.store.snapshot.appState },
+    };
+    const resolved = options.resolveAppState(context);
+
+    if (!resolved || Object.keys(resolved).length === 0) {
+      return undefined;
+    }
+    return resolved;
+  }
+
+  cancel(): TransactionSummary {
+    if (this.cachedSummary) {
+      return this.cachedSummary;
+    }
+
+    if (this.status === "active") {
+      this.manager.markTransactionCanceled(this.id);
+    }
+
+    this.closeTransaction();
+    const status = this.status;
+    this.cachedSummary = {
+      id: this.id,
+      status,
+      historyCommitted: false,
+    };
+    this.ledger.clear();
+    return this.cachedSummary;
+  }
+}

packages/excalidraw/transaction/types.ts

@@ -0,0 +1,83 @@
+import type { ElementUpdate } from "@excalidraw/element";
+
+import type {
+  ExcalidrawElement,
+  ExcalidrawNonSelectionElement,
+} from "@excalidraw/element/types";
+
+import type { ObservedAppState } from "../types";
+
+export type ElementPropName = Extract<keyof ExcalidrawElement, string>;
+
+export type TouchedElementProps =
+  | { kind: "all" }
+  | { kind: "partial"; props: Set<ElementPropName> };
+
+export type ElementChange = {
+  id: ExcalidrawElement["id"];
+  before: ExcalidrawElement | null;
+  after: ExcalidrawElement | null;
+  touchedProps: TouchedElementProps;
+};
+
+/** Per-element ledger record captured during a transaction session. */
+export type TransactionLedgerEntry = {
+  baselineElement: ExcalidrawElement | null;
+  targetElement: ExcalidrawElement | null;
+  touchedProps: TouchedElementProps;
+};
+
+/** Lifecycle state of a transaction. */
+export type TransactionStatus = "active" | "committed" | "canceled";
+
+/** Per-element partial patch used by tx.updateElements(). */
+export type TransactionUpdatableElementType =
+  ExcalidrawNonSelectionElement["type"];
+
+export type TransactionElementOfType<
+  TType extends TransactionUpdatableElementType,
+> = Extract<ExcalidrawNonSelectionElement, { type: TType }>;
+
+export type TransactionElementUpdate<
+  TType extends TransactionUpdatableElementType = TransactionUpdatableElementType,
+> = TType extends TransactionUpdatableElementType
+  ? {
+      id: ExcalidrawElement["id"];
+      type: TType;
+      updates: ElementUpdate<TransactionElementOfType<TType>>;
+    }
+  : never;
+
+/** Final summary returned when a transaction is committed or canceled. */
+export type TransactionSummary = {
+  id: string;
+  status: TransactionStatus;
+  historyCommitted: boolean;
+};
+
+/** Three-way appState context provided to the resolver at commit time. */
+export type AppStateResolverContext = {
+  /** AppState snapshot captured when the transaction was created. */
+  initial: Partial<ObservedAppState>;
+  /** Merged appState intent from all updateScene calls during the transaction. */
+  accumulated: Partial<ObservedAppState>;
+  /** Current live appState at commit time. */
+  live: Partial<ObservedAppState>;
+};
+
+/**
+ * Caller-provided resolver that determines which appState changes are
+ * recorded in the history entry.
+ *
+ * Unlike elements — where per-property conflict detection works because
+ * element properties are largely independent — appState keys are often
+ * interdependent (e.g. selectedElementIds ↔ selectedGroupIds must stay
+ * consistent). The correct merge strategy therefore depends on the
+ * caller's semantic context, not on a generic policy.
+ *
+ * Return the appState delta to record in history, or undefined to skip
+ * appState changes entirely.
+ */
+export type AppStateResolver = (
+  context: AppStateResolverContext,
+) => Partial<ObservedAppState> | undefined;

packages/excalidraw/transaction/undoOverridePlanner.ts

@@ -0,0 +1,283 @@
+import type { StoreDelta, TxUndoOverride } from "@excalidraw/element";
+
+import type { ExcalidrawElement } from "@excalidraw/element/types";
+
+import {
+  TX_UNDO_OVERRIDE_IGNORED_PROPS,
+  collectElementChanges,
+  getElementProp,
+  getElementPropEntries,
+  getUpdatedElementEntries,
+  hasTouchedProp,
+  isPartialTouchedProps,
+  isLedgerValueEqual,
+  serializeConsumedPropKey,
+  serializeIntermediateValue,
+  touchesWholeElement,
+  type ElementUpdatedEntry,
+} from "./diff";
+
+import type {
+  ElementPropName,
+  TouchedElementProps,
+  TransactionLedgerEntry,
+} from "./types";
+
+type TxUndoOverrideCandidate = Omit<TxUndoOverride, "txId">;
+
+/**
+ * Per-element-prop history of tx intermediate values.
+ *
+ * We keep:
+ * - the full sequence for exact deep-equality fallback
+ * - a serialized signature set for fast negative lookups
+ * - the latest value for the most common positive lookup path
+ */
+class TxIntermediateValueHistory {
+  private readonly values: unknown[] = [];
+  private readonly signatures = new Set<string>();
+  private latestValue: unknown;
+  private hasLatestValue = false;
+
+  /** Appends a new intermediate value, skipping consecutive duplicates. */
+  add(value: unknown) {
+    if (this.hasLatestValue && isLedgerValueEqual(this.latestValue, value)) {
+      return;
+    }
+
+    this.values.push(value);
+    this.signatures.add(serializeIntermediateValue(value));
+    this.latestValue = value;
+    this.hasLatestValue = true;
+  }
+
+  /** Returns whether the candidate appeared in this tx prop history. */
+  contains(candidate: unknown) {
+    const candidateSignature = serializeIntermediateValue(candidate);
+    if (!this.signatures.has(candidateSignature)) {
+      return false;
+    }
+
+    if (
+      this.hasLatestValue &&
+      isLedgerValueEqual(this.latestValue, candidate)
+    ) {
+      return true;
+    }
+
+    return this.values.some((value) => isLedgerValueEqual(value, candidate));
+  }
+}
+
+/**
+ * Tracks tx intermediate values and computes undo baseline override markers
+ * for durable user deltas recorded while tx is active.
+ *
+ * High-level flow:
+ * 1. `recordStep()` observes every in-tx scene mutation and records the
+ *    intermediate value reached by each touched element prop.
+ * 2. When a durable user delta is about to be recorded,
+ *    `collectCandidatesForDurableDelta()` checks whether that delta's
+ *    deleted-baseline values match any tx intermediate value.
+ * 3. If they do, we emit override candidates so undo can restore the pre-tx
+ *    baseline once the tx has ended.
+ * 4. `markConsumed()` ensures only the first polluted durable entry for a
+ *    given element+prop gets patched; later user actions keep their own
+ *    action-local undo baseline.
+ */
+export class TxUndoOverridePlanner {
+  private readonly intermediateValuesByElementProp = new Map<
+    string,
+    Map<ElementPropName, TxIntermediateValueHistory>
+  >();
+  private readonly consumedOverridePropKeys = new Set<string>();
+
+  /** Resets planner state when the transaction finishes. */
+  clear() {
+    this.consumedOverridePropKeys.clear();
+    this.intermediateValuesByElementProp.clear();
+  }
+
+  /** Records per-prop intermediate values reached by one in-tx scene step. */
+  recordStep(
+    before: ReadonlyMap<string, ExcalidrawElement>,
+    after: ReadonlyMap<string, ExcalidrawElement>,
+  ) {
+    for (const change of collectElementChanges(before, after)) {
+      const { id: elementId, after: afterElement, touchedProps } = change;
+
+      if (!afterElement || !isPartialTouchedProps(touchedProps)) {
+        continue;
+      }
+
+      for (const prop of touchedProps.props) {
+        this.recordIntermediateValue(
+          elementId,
+          prop,
+          getElementProp(afterElement, prop),
+        );
+      }
+    }
+  }
+
+  /**
+   * Collects override candidates for one durable user delta recorded while the
+   * tx is active.
+   */
+  collectCandidatesForDurableDelta(
+    delta: StoreDelta,
+    getLedgerEntry: (elementId: string) => TransactionLedgerEntry | undefined,
+    reservedConsumedKeys: Set<string>,
+  ): TxUndoOverrideCandidate[] {
+    const candidates: TxUndoOverrideCandidate[] = [];
+
+    for (const [elementId, deltaEntry] of Object.entries(
+      getUpdatedElementEntries(delta),
+    )) {
+      const ledgerEntry = getLedgerEntry(elementId);
+      if (!ledgerEntry) {
+        continue;
+      }
+
+      const elementCandidates = this.collectCandidatesForElement(
+        elementId,
+        deltaEntry,
+        ledgerEntry,
+        reservedConsumedKeys,
+      );
+      if (elementCandidates.length > 0) {
+        candidates.push(...elementCandidates);
+      }
+    }
+
+    return candidates;
+  }
+
+  /** Evaluates one element's updated entry against the tx ledger snapshot. */
+  private collectCandidatesForElement(
+    elementId: string,
+    deltaEntry: ElementUpdatedEntry,
+    ledgerEntry: TransactionLedgerEntry,
+    reservedConsumedKeys: Set<string>,
+  ): TxUndoOverrideCandidate[] {
+    const { baselineElement, touchedProps } = ledgerEntry;
+    if (!baselineElement || touchesWholeElement(touchedProps)) {
+      return [];
+    }
+
+    const candidates: TxUndoOverrideCandidate[] = [];
+    for (const [prop, deletedValue] of getElementPropEntries(
+      deltaEntry.deleted,
+    )) {
+      const candidate = this.createCandidateForProp({
+        elementId,
+        prop,
+        deletedValue,
+        baselineElement,
+        touchedProps,
+        reservedConsumedKeys,
+      });
+      if (candidate) {
+        candidates.push(candidate);
+      }
+    }
+
+    return candidates;
+  }
+
+  /**
+   * Returns an override candidate for one element+prop when the durable delta's
+   * deleted baseline was polluted by a tx intermediate value.
+   */
+  private createCandidateForProp(args: {
+    elementId: string;
+    prop: ElementPropName;
+    deletedValue: unknown;
+    baselineElement: ExcalidrawElement;
+    touchedProps: TouchedElementProps;
+    reservedConsumedKeys: Set<string>;
+  }): TxUndoOverrideCandidate | null {
+    const { elementId, prop, deletedValue, baselineElement, touchedProps } =
+      args;
+
+    if (
+      TX_UNDO_OVERRIDE_IGNORED_PROPS.has(prop) ||
+      !hasTouchedProp(touchedProps, prop)
+    ) {
+      return null;
+    }
+
+    const consumedPropKey = serializeConsumedPropKey(elementId, prop);
+    // Override only the first polluted user entry for this element+prop.
+    // Later user actions should keep action-local undo baselines.
+    if (
+      this.consumedOverridePropKeys.has(consumedPropKey) ||
+      args.reservedConsumedKeys.has(consumedPropKey)
+    ) {
+      return null;
+    }
+
+    if (!this.matchesIntermediateValue(elementId, prop, deletedValue)) {
+      return null;
+    }
+
+    return {
+      elementId,
+      prop,
+      expectedInsertedValue: deletedValue,
+      preTxBaselineValue: getElementProp(baselineElement, prop),
+      consumedKey: consumedPropKey,
+    };
+  }
+
+  /** Marks an element+prop override as consumed by an earlier durable entry. */
+  markConsumed(consumedPropKey: string) {
+    this.consumedOverridePropKeys.add(consumedPropKey);
+  }
+
+  /** Returns the per-prop history map for one element, creating it if needed. */
+  private getOrCreatePropValues(elementId: string) {
+    const existing = this.intermediateValuesByElementProp.get(elementId);
+    if (existing) {
+      return existing;
+    }
+
+    const created = new Map<ElementPropName, TxIntermediateValueHistory>();
+    this.intermediateValuesByElementProp.set(elementId, created);
+    return created;
+  }
+
+  /** Appends one observed intermediate value for an element prop. */
+  private recordIntermediateValue(
+    elementId: string,
+    prop: ElementPropName,
+    value: unknown,
+  ) {
+    const propValues = this.getOrCreatePropValues(elementId);
+    const history = propValues.get(prop);
+    if (history) {
+      history.add(value);
+      return;
+    }
+
+    const nextHistory = new TxIntermediateValueHistory();
+    nextHistory.add(value);
+    propValues.set(prop, nextHistory);
+  }
+
+  /** Checks whether a durable delta baseline matches any tx intermediate value. */
+  private matchesIntermediateValue(
+    elementId: string,
+    prop: ElementPropName,
+    candidate: unknown,
+  ) {
+    const history = this.intermediateValuesByElementProp
+      .get(elementId)
+      ?.get(prop);
+    if (!history) {
+      return false;
+    }
+
+    return history.contains(candidate);
+  }
+}

packages/excalidraw/types.ts

@@ -796,6 +796,9 @@ export type AppClassProperties = {
   files: BinaryFiles;
   editorInterface: App["editorInterface"];
   scene: App["scene"];
+  store: App["store"];
+  transactionManager: App["transactionManager"];
+  createTransaction: App["createTransaction"];
   syncActionResult: App["syncActionResult"];
   fonts: App["fonts"];
   pasteFromClipboard: App["pasteFromClipboard"];