Phase 3: The Generate-Validate Loop · 40 min · Git · Claude Code · Python
Git as a Safety Net for AI Code
Commit after every validated step, not at the end of the session — the commit is what makes 'that went wrong, revert it' possible instead of theoretical.
Hiring signal: Demonstrating that you commit AI-generated work incrementally, with real messages and traceability, is concrete evidence of the audit discipline production teams actually require before trusting agent-written code.
What you will learn
- Commit after each validated generation step so a bad step can be reverted precisely, without losing prior progress
- Read a diff and restate in plain English what changed and why, as a validation check before accepting it
- Use branch-per-feature to limit the blast radius of an exploratory or risky AI-assisted session
- Audit a commit log for clear messages and traceability back to the spec or task that motivated each change
Introduction
Git as a Safety Net for AI Code
An agent works through a four-task feature in one long, uninterrupted session, and the engineer commits once, at the very end, after everything looks done. Task three's implementation turns out to be subtly wrong — it passes the happy-path test but breaks an edge case discovered a day later — and now "revert task three" means reconstructing which lines belong to which task inside one enormous diff, because nothing marked the boundaries when they actually happened. A different engineer, running the same four-task plan, commits after each task is generated and validated individually. When task three turns out wrong, reverting is exactly one command: go back to the commit right after task two, before task three's changes existed at all. Same bug, same feature, completely different cost to fix, and the difference was entirely about commit granularity, decided before any of this happened.
Commits as checkpoints, not archives
Treating git as an archive means committing rarely, in large batches, mostly as a record of "here's what got done." Treating it as a safety net means committing after every validated step — the walking skeleton, then each task from the hardest-first plan in c12-01-5 — so that every commit is a known-good state you can return to. This isn't about commit message ceremony; it's about making "that was wrong, go back" a real, cheap, precise operation instead of an archaeology project through a diff nobody marked the seams of.
The test for commit granularity
Ask: if this specific commit turns out to be wrong tomorrow, can I revert exactly it, and only it, without losing anything else? If the answer requires untangling multiple unrelated changes first, the commit was too large. Commit at the boundary of each validated task, not at the boundary of "I feel like committing now."
Unlock the full lesson
You've read the first 2 sections. The rest of this lesson covers Reading diffs in plain English, Branch-per-feature as a blast-radius limiter, The audit trail, Build It — plus a hands-on lab, quiz, and project artifact.
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