Cross-Repo Change

The rule: at every moment between the first deploy and the last, every deployed version of every repo must work with every other. You get there by ordering the changes, not by deploying "at the same time" (which never actually happens).

Step 1: Inputs

• The impact-analysis report (run it first if it doesn't exist). You need the list of consumers per repo.
• The repo map's Connections table: how the repos talk (HTTP, shared DB, queue, webhook, shared package).
• How each repo deploys and how long it takes; mobile apps are the slow case since old versions stay in the wild.

Step 2: Order the changes

Default order for a provider/consumer change (backend API used by web-app, say):

1. Provider expands. Backend adds the new field/endpoint/behavior without removing anything. Contract tests updated to cover the new shape (contract-tests). Deploy.
2. Consumers switch. Each consumer moves to the new shape. Deploy each.
3. Provider contracts. Backend removes the old shape once every consumer has deployed (and, for mobile, once old app versions are below your support threshold). Deploy.

Other cases: