The plan stands, the tag final-start is in place, and now you build. This lesson is the longest of the course and the one with the least new text. It gives you a loop that you run through for every seam of your plan, and a script that checks the history. How each individual step works is in lessons M2 to M6; here it says when to open them.

The loop per seam

Every seam from seams.csv goes through the same six steps, in this order:

Step What you do Where it is
1. Safety net record the current behavior before anything is changed: test, copy of the database lesson M2.1
2. Change implement the seam, so small that it fits into one commit the lesson in the table below
3. Test a test that records the new version, and a counter-check that turns it red lesson M2.1, M4.3 (comparison of old and new)
4. Commit one step, one commit, title in Conventional Commits form house rules, lesson M1.2
5. Evidence a command or test with an exit code that the reviewer can repeat the house rules: the exit code counts
6. Plan tick off or change the seam in plan.md, with one sentence lesson M1.4: the plan is a working document

The order is intentional. Whoever changes first and writes a test afterward has only recorded what the new code does, not what the old one did. If you find nothing in step 1 that can be recorded, that is a finding: Then this seam is not yet ready and moves back in the order.