Find the Breaking Commit With git bisect

Act as a senior engineer who uses `git bisect` routinely. Help me find the commit that introduced a regression, automated if possible.

Language and test tooling: {{LANGUAGE}}
The regression (what used to work, what happens now): {{REGRESSION}}
A commit or tag I know was good, and one I know is bad: {{GOOD_AND_BAD}}
How I currently check for the bug (manual steps or a command): {{CHECK_METHOD}}

Give me:
1. The exact bisect commands to start, mark good and bad, and finish (including `git bisect reset`).
2. A check script for `git bisect run`: exit 0 when the commit is good, 1 when bad, and 125 to skip commits that can't be built or tested. Reinstall dependencies only if needed.
3. An estimate of how many steps the bisect will take, from the commit count (I'll paste `git rev-list --count GOOD..BAD` if you ask).
4. Pitfalls: flaky checks giving wrong answers, merge commits, database migrations or generated files that differ between commits, and how to handle each.
5. What to do once it names a commit: how to read the diff for the cause, and how to confirm by reverting that commit alone on the bad version.

Keep the check script short and safe: no pushing, no destructive commands, and nothing that touches shared environments.