Debugger Agent

$ npm test -- user.test.ts

FAIL tests/user.test.ts
  ✕ should update user profile (52ms)

Error: Expected status 200, received 500
    at Object.<anonymous> (tests/user.test.ts:45:7)

Stack trace:
  at updateProfile (src/api/user.ts:89)
  at handler (server/routes/user.ts:34)

Type: Regression (test passed 3 days ago)

Hypothesis 1 (70%): [Most likely cause]
  Evidence for:
    - [Supporting fact 1]
    - [Supporting fact 2]
  Evidence against:
    - [Contradicting fact]
  Test:
    - [How to verify this hypothesis]

Hypothesis 2 (20%): [Alternative cause]
  Evidence for:
    - [Supporting fact]
  Evidence against:
    - [Contradicting fact]
  Test:
    - [How to verify]

Hypothesis 3 (10%): [Unlikely but possible]
  Evidence for:
    - [Supporting fact]
  Evidence against:
    - [Contradicting fact]
  Test:
    - [How to verify]

Testing Hypothesis 1: Profile API returns null for deleted users

1. Checking database:
   $ psql -c "SELECT * FROM users WHERE id = 12345"
   (0 rows)
   
   ✓ User 12345 does not exist!

2. Reading getUserData code:
   src/services/user.ts:142
   
   const user = await db.findUser(userId);
   return user.id; // ← Error here if user is null
   
   ✓ No null check before accessing user.id

3. Checking git history:
   $ git log --oneline --since="1 week ago" -- src/services/user.ts
   
   abc1234 Add user deletion feature
   
   ✓ User deletion added 3 days ago, matches timeline

4. Checking similar code:
   src/services/admin.ts has:
   
   const user = await db.findUser(userId);
   if (!user) return null;
   return user.id;
   
   ✓ Other code properly checks for null

CONCLUSION: Hypothesis 1 confirmed!
Root cause: getUserData doesn't handle null user

ROOT CAUSE: getUserData doesn't handle deleted users
WHERE: src/services/user.ts:142
WHY: User deletion feature was added without updating dependent code
SINCE: Commit abc1234 (3 days ago, March 5th)

Details:
When a user is deleted, db.findUser(userId) returns null.
getUserData tries to access user.id without checking if user exists.
This throws "Cannot read property 'id' of undefined".

Other parts of the codebase (admin.ts) properly check for null,
but this code path was missed during the deletion feature implementation.

FIX: Add null check before accessing user properties

CHANGES:
  - src/services/user.ts:142 - Add null check
    Before:
      const user = await db.findUser(userId);
      return user.id;
    
    After:
      const user = await db.findUser(userId);
      if (!user) return null;
      return user.id;
  
  - tests/services/user.test.ts:89 - Add deleted user test
    Test that getUserData returns null for deleted users

RISK: Low
- Minimal change, follows existing patterns
- Other code already returns null for missing users
- Backward compatible (null is expected return type)

TESTS:
1. Existing tests should still pass
2. New test: getUserData with deleted user ID returns null
3. Manual: Profile page shows "User not found" instead of crashing

User: The user profile page is crashing in production

=== STEP 1: REPRODUCE ===

Reproducing error...
Checking production logs...

Error found:
TypeError: Cannot read property 'id' of undefined
    at getUserData (src/services/user.ts:142:15)
    at renderProfile (src/pages/Profile.tsx:28:9)

User ID: 12345
Timestamp: 2026-03-08 14:32:01

Running test locally...
Test passes with existing user.
Test fails with user ID that doesn't exist.

Classification: Regression
- Feature worked before
- Started 3 days ago after user deletion feature deployed

=== STEP 2: HYPOTHESIZE ===

Hypothesis 1 (70%): getUserData doesn't handle deleted users
  Evidence for:
    - Error message indicates undefined user object
    - User deletion feature added recently
    - Error only happens for specific user IDs
  Evidence against:
    - Should have been caught in testing
  Test:
    - Check if user 12345 exists in database
    - Read getUserData implementation

Hypothesis 2 (20%): Cache returning stale data
  Evidence for:
    - Using Redis for user data
    - Deletion might not invalidate cache
  Evidence against:
    - Cache has 5min TTL, user deleted 2 days ago
  Test:
    - Check cache invalidation on user deletion

Hypothesis 3 (10%): Database replication lag
  Evidence for:
    - Using read replicas
  Evidence against:
    - Lag is typically < 1s, user deleted days ago
  Test:
    - Query primary database directly

=== STEP 3: INVESTIGATE ===

Testing Hypothesis 1...

Checking database:
$ psql production -c "SELECT * FROM users WHERE id = 12345"
(0 rows)

✓ User 12345 does not exist

Reading getUserData code:
src/services/user.ts:142

export async function getUserData(userId: number) {
  const user = await db.findUser(userId);
  return user.id; // ← No null check!
}

✓ Code doesn't handle null user

Checking git history:
$ git log --oneline --since="1 week ago" -- src/services/user.ts

abc1234 Add user deletion feature
xyz5678 Update type definitions

$ git show abc1234

+ async function deleteUser(userId: number) {
+   await db.users.delete({ id: userId });
+ }

✓ Deletion feature added but dependent code not updated

Searching for similar patterns:
$ grep -r "db.findUser" src/

src/services/admin.ts:
const user = await db.findUser(userId);
if (!user) return null;
return user.id;

✓ Other code properly checks for null!

Hypothesis 1 confirmed.

=== STEP 4: ROOT CAUSE ===

ROOT CAUSE: getUserData doesn't handle deleted users
WHERE: src/services/user.ts:142
WHY: User deletion feature added without updating dependent code
SINCE: Commit abc1234 (March 5th, 2026)

Explanation:
When a user is deleted via the new deleteUser function,
db.findUser(userId) returns null. getUserData attempts to
access user.id without checking if user exists, causing
the TypeError.

Other parts of the codebase (e.g., admin.ts) properly
handle the null case, but this code path was missed
during the deletion feature implementation.

=== STEP 5: FIX PROPOSAL ===

FIX: Add null check before accessing user properties

CHANGES:
  src/services/user.ts:142
    Before:
      export async function getUserData(userId: number) {
        const user = await db.findUser(userId);
        return user.id;
      }
    
    After:
      export async function getUserData(userId: number) {
        const user = await db.findUser(userId);
        if (!user) return null;
        return user.id;
      }
  
  tests/services/user.test.ts:89
    Add test case:
      it('returns null for deleted user', async () => {
        const result = await getUserData(99999);
        expect(result).toBeNull();
      });

RISK: Low
- Minimal change following existing patterns
- Backward compatible (null is valid return type)
- Matches how other services handle missing users

TESTS:
1. Run existing test suite (should all pass)
2. New test: getUserData with non-existent user returns null
3. Manual: Visit profile page for deleted user, should show 404
4. Check Profile.tsx handles null return value gracefully

Waiting for approval...

User: approved

Implementing fix...
src/services/user.ts updated ✓
tests/services/user.test.ts updated ✓

Running tests...
All tests pass ✓

Fix complete!

[LEARN] Debugging: Always check git blame for recent changes in error area
[LEARN] Debugging: When adding deletion features, search for all usages
[LEARN] Convention: All db.find* calls should check for null before accessing properties