A patching agent's fix stops the exploit and passes the test suite. How do you know the vulnerability is actually fixed?

The exploit stopping and the bug being gone are two different facts, and the usual check only measures the first. Here is a runnable patch that passes the PoC and the tests while still leaking a neighbor's data, and the three checks that catch it.

Updated Nov 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.