# Feature: setting to disable Undo Create Diff (prevents 0-byte / 524288 truncation)

**URL:** <https://forum.cursor.com/t/feature-setting-to-disable-undo-create-diff-prevents-0-byte-524288-truncation/171408>\
**Category:** Feature Requests\
**Tags:** checkpoints, review\
**Created:** [September 12, 2026, 6:51am UTC](https://forum.cursor.com/t/feature-setting-to-disable-undo-create-diff-prevents-0-byte-524288-truncation/171408 "2026-09-12T06:51:14Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![gunhun322](https://avatars.discourse-cdn.com/v4/letter/g/e36b37/32.png) [@gunhun322](https://forum.cursor.com/u/gunhun322)\
**Post date:** [September 12, 2026, 6:51am UTC](https://forum.cursor.com/t/feature-setting-to-disable-undo-create-diff-prevents-0-byte-524288-truncation/171408/1 "2026-09-12T06:51:14Z")

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### Describe the request

# Feature / Bug: Please provide a setting to disable Undo Create Diff (mass file wipe / 524288 truncation)

**Related:** [Bug report: mass local file wipe via Undo Create Diff on restart](https://forum.cursor.com/t/bug-report-mass-local-file-wipe-via-undo-create-diff-on-restart/167209)  
**Request:** Product setting to **disable / opt out of Undo Create Diff** bulk write-back. Current mitigations (`timeline.excludeSources`, Agent rules) cannot block this path.

## Environment

- OS: Windows Server / Win10 build 10.0.14393 (win32)
- Project: large monorepo (API + Web + C++ Qt)
- Local History: kept **enabled** for recovery (`workbench.localHistory.enabled: true`)
- Already applied: `timeline.excludeSources: ["timeline.localHistory"]` — only hides Timeline UI, does **not** stop Undo Create Diff

## What happened (2026-09-12 ~14:24–14:27 local)

Same failure mode as known “mass wipe via Undo Create Diff”:

| File | Symptom |
| --- | --- |
| `packages/api/src/routes/sales.ts` | Truncated to exactly **524288** bytes (half EOF → esbuild `Unexpected end of file`) |
| `packages/api/src/routes/delivery-special-price.ts` | Written to **0 bytes** → Express `Router.use() requires a middleware function but got a Object` |
| `packages/api/src/routes/counter-reconciliation.ts` | Written to **0 bytes** |

Recovery: Volume Shadow Copy (`HarddiskVolumeShadowCopy17`, 14:00) + re-apply intentional edits. Truncated copy kept as `sales.ts.truncated-before-restore-*`.

## Evidence (Local History)

In `%APPDATA%\Cursor\User\History\*\entries.json`, between **14:26:34 and 14:27:13** local time:

- **809** history entry files updated in ~40 seconds
- **All 809** had `source: "Undo Create Diff"` (`undoCount=809`)
- Span covered API / web-admin / C++merchant-client / wx-admin / docs / migrations — classic **bulk Undo Create Diff** , not a single Agent `Write` empty file

This matches prior incidents on the same machine (documented in project rules: 2026-08-16 / 08-22 / 08-23 / 09-09).

## Why we need a product switch

We already:

1. Forbid Agent empty/`Write` overwrite of existing sources (workspace rules)
2. Hide Local History from Timeline to reduce mis-clicks
3. Instruct: never use Timeline one-click Undo Create Diff; prefer Checkpoint / per-file restore / VSS / Git

**None of these can disable** Composer/Agent Review **Undo / Undo All** or session-restore paths that still emit `Undo Create Diff` and rewrite disk.

## Expected product behavior

Please add one of:

1. **Setting** e.g. `cursor.agent.disableUndoCreateDiff: true` or `cursor.composer.bulkUndoDiff: "off"` — refuse bulk Undo Create Diff write-back
2. Or: Undo Create Diff must **never** write empty / truncated content; fail closed and keep previous bytes
3. Or: require explicit typed confirmation for Undo affecting \>N files

Also: document that `timeline.excludeSources` ≠ disabling Undo Create Diff.

## Mitigations we added locally (insufficient)

```json
"files.restoreUndoStack": false,
"workbench.restoreEditors": "none"

```

(plus existing Timeline exclude + Local History kept on)

## Does this stop us from using Cursor?

No — but it repeatedly destroys large source files and burns recovery time. We need an official kill-switch.

* * *

**Paste target:** [Bug Reports - Cursor - Community Forum](https://forum.cursor.com/c/bug-reports/6) (or Feature Requests) → New Topic  
**Title suggestion:** `Feature: setting to disable Undo Create Diff (prevents 0-byte / 524288 truncation)`

---

<div class="post-metadata">

**Author:** ![Colin](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/colin/32/90452_2.png) [@Colin](https://forum.cursor.com/u/Colin)\
**Post date:** [September 14, 2026, 9:14am UTC](https://forum.cursor.com/t/feature-setting-to-disable-undo-create-diff-prevents-0-byte-524288-truncation/171408/9 "2026-09-14T09:14:08Z")

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Hey @gunhun322, thanks for the detailed write-up and for the Local History evidence, that lines up with what we’re seeing!

To be clear, this isn’t something you misconfigured. On startup Cursor re-applies any agent edits that are still pending review, and on Windows that re-save can leave files empty or cut off if it’s interrupted. It’s a known issue the team is actively working on, and some related fixes have already shipped in recent versions. I can’t share a timeline for the rest yet, but we’ll share an update when we have one.

The most reliable way to avoid it in the meantime is to clear every pending agent change (Keep All or Undo All in Review Changes) before you quit, update, or restart, and to keep committing often. Discarding via git alone doesn’t clear the pending state, so those files can be rewritten again on the next launch until they’re resolved in Cursor.