DeepSeek Debug and Fix: TypeScript cross-origin security in customer support portal

I need help debugging and fixing a cross-origin security issue in my TypeScript customer support portal project.

**Leverage DeepSeek strengths:** Debugging requires systematic reasoning, understanding complex code interactions, and producing correct fixes, which are your strengths.

**Tech stack:** Nest.js + GraphQL
**My experience level:** junior developer

## Debugging Session Framework

### Step 1: Problem Description Template
Help me describe the bug systematically:
- **Expected behavior:** What should happen
- **Actual behavior:** What is happening instead
- **Reproduction steps:** Minimal steps to trigger the issue
- **Frequency:** Always, intermittently, or under specific conditions
- **Environment:** Development, staging, or production
- **Recent changes:** What changed before the bug appeared

### Step 2: Diagnostic Approach for cross-origin security Issues
Walk me through a systematic debugging process:
1. What information to gather first
2. Which logs, metrics, or traces to examine
3. How to narrow down the root cause
4. Common causes of cross-origin security issues in TypeScript with Nest.js + GraphQL
5. Debugging tools and commands specific to this stack

### Step 3: Common cross-origin security Patterns in TypeScript
List the top 10 most common causes of cross-origin security bugs in TypeScript applications:
For each pattern:
- Description of the bug pattern
- Code example showing the buggy code
- Explanation of why it causes problems
- Corrected code with the fix
- How to prevent it in the future (linting rules, testing, code review checklist)

### Step 4: Fix Implementation Guide
When I share my specific code, analyze it for:
- The root cause of the cross-origin security issue
- Any related bugs that might be lurking nearby
- The minimal fix that resolves the immediate issue
- A more thorough fix that prevents the class of bugs
- Regression test to ensure the bug does not return

### Step 5: Prevention Strategies
- Testing patterns that would have caught this cross-origin security bug
- Static analysis or linting rules to add
- Code review checklist items for cross-origin security issues
- Monitoring and alerting to detect this issue in production
- Architectural patterns that make cross-origin security bugs less likely

### Step 6: Knowledge Capture
- Document the root cause and fix for the team
- Create a runbook for diagnosing similar issues
- Update development guidelines to prevent recurrence

Please share your code and error messages, and I will walk through this framework with you step by step.