Cursor Keeps Breaking My Working Code: How to Stop the Drift

Cursor is the default co-pilot for most builders we meet. It’s fast, context-aware, and wildly capable. It’s also the reason so many large AI-built apps land in triage. Put Cursor on a 50,000-line repo with no boundaries and it acts like an excited junior engineer: eager to help, unaware of consequences.

Here’s the hardened workflow we recommend when Cursor keeps “fixing” the wrong files.

The Pattern: Change A, Break B #

• You ask Cursor to update onboarding copy.
• Cursor scans your React tree, updates prop names “for consistency,” and rewrites the analytics hook.
• Checkout fails because the analytics hook now emits a different event name.

Repeat this a dozen times and you’re convinced Cursor is sabotaging you. In reality, it’s doing exactly what you asked—just without constraints.

Why Cursor Does This (for Large Projects) #

1. Full-project visibility: Cursor indexes your entire repo. When it receives a prompt, it proactively aligns related files.
2. Heuristic refactors: It optimizes patterns (renaming variables, extracting functions) even if you only asked for a small change.
3. Lack of "do-not-touch" markers: Unless you specify safe zones, Cursor assumes everything is fair game.
4. Prompts without exit criteria: "Make sure this works" invites the model to chase ripple effects indefinitely.

Step 1: Install Guardrails in Cursor #

1. Define Workspace Rules #

In .cursorrules (or the Workspace Prompt), add:

You may only modify the following paths unless explicitly instructed otherwise:
- app/(marketing)/**
- app/api/onboarding/**
If you believe another path must change, stop and ask.

Keep the list tight. Expand only when necessary.

2. Label No-Go Zones #

Add code comments like:

// 🚫 DO NOT MODIFY: Critical billing logic. Ask before touching.

Cursor respects explicit language. Make it loud.

3. Limit Diff Radius #

Use Cursor’s settings to cap maximum file changes per diff. If a change requires more files, break it into separate prompts.

Step 2: Change How You Prompt #

1. Scope Before You Code #

Prompt template:

Step 1: Describe the current behavior of <component>.
Step 2: List the files you expect to touch.
Step 3: Wait for confirmation before writing code.

This forces Cursor to verbalize intent. You approve or redirect before any diff exists.

2. Demand Post-Change Reports #

After a diff, ask:

Summarize exactly what changed, file by file. Mention tests updated and implications.

Compare the summary to the diff. Anything unexpected? Reject.

3. Scripted Smoke Tests #

Require Cursor to update scripts/run-smoke.ts whenever it edits critical flows. If it claims tests pass, ask for the command output.

Step 3: Restructure Your Repo for Cursor-Friendliness #

1. Decouple Modules #

Split monolithic directories into bounded contexts. Cursor is less likely to drift if React, API routes, workers, and prompts live in clearly separated folders.

2. Introduce Public Interfaces #

Wrap critical logic behind exported functions. Cursor will respect module boundaries if public APIs are obvious and well-documented.

3. Document Contracts #

Add README files per domain explaining invariants. Cursor often leaves these alone when they’re explicit.

Step 4: Automate Drift Detection #

• Git Hooks: Fail commits that touch banned directories without a #cursor-approved tag.
• CI Scripts: Compare file lists between prompts and diffs.
• Observability: Trigger alerts when key metrics change unexpectedly after a merge.

Step 5: Blend Cursor with Human Oversight #

• Schedule weekly “Cursor Review” sessions to analyze where it helped or hurt.
• Pair Cursor with Claude or ChatGPT to cross-check diff reasoning.
• Keep a changelog of major guardrail updates.

Workarounds Founders Use (and Whether They Work) #

The best solution isn’t abandoning Cursor; it’s taming it.

The Automated Approach: Use Giga #

Instead of manually maintaining workspace rules and documentation, Giga automatically:

• Generates project-specific context rules that update as you code
• Creates persistent AI memory of your codebase structure
• Helps Cursor understand which files connect to which features
• Prevents cascade failures from changes spreading unexpectedly
• Works with Cursor, VSCode, Claude Code, and other AI tools

Setup (5 minutes):

npm install -g giga-cli
giga init
giga connect cursor

What changes:

• Cursor understands your full project architecture
• AI changes only the files relevant to your request
• No more surprise breaks in unrelated features
• Self-learning memory improves over time

Keep Cursor on Your Side #

Manual approach: Ship context documentation and READMEs so Cursor knows the architecture.

Automated approach: Use Giga to maintain complete project understanding automatically.

Either way, track prompt changes in version control and let automated tests catch regressions.

Once Cursor has complete project visibility (whether through manual rules or Giga), it becomes incredibly powerful. You'll ship faster and stay in control.