Agents optimize for completing tasks, not solving problems.

Your agent says it completed the task. Your tests are green. Your deployment succeeded. Everything looks perfect.

Then you check the actual output and it's completely wrong.

This happened to us three times last week. Our coding agent would confidently report "Task completed successfully" while shipping code that didn't work, tests that passed but tested the wrong thing, or features that looked right but broke the user flow.

The problem isn't the agent lying — it's that success and completion aren't the same thing.

Your agent optimizes for completing its instructions, not for solving your actual problem. If you ask it to "add a login button," it'll add a button labeled "Login" and call it done. Whether that button actually logs users in is a different question entirely.

Here's the pattern that caught our last three silent failures:

## Completion Verification Checklist

1. **Implementation Check**: Code/feature exists
2. **Functional Check**: Code/feature works as intended
3. **Integration Check**: Doesn't break existing functionality
4. **User Check**: Solves the original problem
5. **Edge Case Check**: Handles failure modes gracefully

We built this into our agent's completion routine. Now when it finishes a task, it runs through each verification step before reporting success.

The game-changer was step 4 — making the agent verify it solved the original problem, not just implemented the requested solution. This caught the login button that didn't actually authenticate users, the search feature that couldn't handle empty results, and the API endpoint that returned data in the wrong format.

Pro tip: Add "Test the happy path and one failure case" to every completion checklist. Most silent failures happen when things don't go perfectly.

For coding tasks, we added a sixth check: "Run the code and verify the output matches expectations." Sounds obvious, but our agent was shipping functions that looked correct but returned undefined, API calls that succeeded but ignored the response, and UI components that rendered but didn't respond to clicks.

The verification loop adds 30 seconds to each task but saves hours of debugging. More importantly, it catches the failures that would otherwise surface in production or user reports.

Your agent should be more skeptical of its own work than you are. If it's not actively looking for ways it might be wrong, it'll confidently ship broken work forever.