[evgeny-simplex]

Plan: a reduced CI build for simplex-chat, and the agent guide for building and testing each scope.

• A draft pull request and a manual run (workflow_dispatch) run one Linux job, ubuntu-22.04 x86_64, which builds and tests every changed scope: core (cabal at -O0, selected tests), Kotlin (compile and unit tests), packages (nodejs, types, python) and other scopes (scope-tests.sh). One macOS job runs only when iOS code changed.
• The full matrix runs when the pull request is marked ready for review and on pushes to master, stable and tags.
• Test selection, names and syntax as in ci: one reduced build job on draft pull requests and manual runs simplex-chat/simplexmq#1986: dispatch input tests, a ci-tests block in the draft description, --fail-on=empty.
• Scopes without CI tests are listed; the agent that changes one adds its build and tests to CI in the same pull request.
• aarch64: a 10-pair experiment on throwaway fork branches, with a decision rule for switching the reduced job to ubuntu-22.04-arm.
• Measured: "Run tests" fails in 27 of 37 recent 22.04 runs; the hspec suite takes 707-844 s on 22.04.

Open questions Q2 (fork cache seeding), Q4 (app workflow delivery) and Q5 (build.yml in the iOS globs) are at the end of the plan.