Part 3 — what moved, and what the old numbers mean now
Part 3 was written as twenty-four chapters in the order the work happened. It now reads as twenty-six chapters in eight movements, each movement one subject, and the chapters inside a movement sit next to each other. Two chapters were split in half rather than compressed, which is where the two extra numbers come from.
Every old address still works — the old URLs redirect permanently to the new ones, in both languages. The numbers are the part that changed meaning. 21 of the 26 chapter numbers name a different chapter than they did before. Only 1, 2 and 7 still mean what they meant, and 25 and 26 are numbers Part 3 never had.
If you followed the previous Part 3
Recreate your development database before continuing. A migration belongs to the chapter that introduces it, and seven chapters moved — so seven migrations were renumbered and two were divided differently. The SQL is unchanged and no table differs; the filenames do, and a migration ledger records which filenames it has applied. A database migrated in the old order will be asked to apply nine migrations under new names and will refuse each one, saying the tables already exist. Nothing is wrong with that database — it simply cannot be upgraded into this ordering, so the reworked series starts its schema from scratch.
By movement
I — The tenant, the credential, and the vocabulary
II — One event, written once
III — The domain a customer can use
IV — The socket, continued from Part 2
VI — Someone else's system
Old number → new number
The reverse direction, for a link or a note that names a chapter by its old ordinal. Two old chapters appear twice, because each became two chapters.