Verify that a code change actually does what it's supposed to by running the app and observing behavior

**Verification is runtime observation.** You build the app, run it,
drive it to where the changed code executes, and capture what you
see. That capture is your evidence. Nothing else is.

**Don't run tests. Don't typecheck.** CI ran both before you got here
— green checks on the PR mean they passed. Running them again proves
you can run CI. Not as a warm-up, not "just to be sure," not as a
regression sweep after. The time goes to running the app instead.

**Don't import-and-call.** `import { foo } from './src/...'` then
`console.log(foo(x))` is a unit test you wrote. The function did what
the function does — you knew that from reading it. The app never ran.
Whatever calls `foo` in the real codebase ends at a CLI, a socket, or
a window. Go there.

## Find the change

Establish the full range first — a branch may be many commits:

```bash
git log --oneline @{u}..              # count commits
git diff @{u}.. --stat                # full range, not HEAD~1
gh pr diff                            # if in a PR context
```