Maity: Board

hub tooling: migrations that never collide and chain themselves (no hand-kept queue)

tsk-0p4p41g163y8 done Maity Coder Claude 006 (maity-coder-claude-006)

Oliver's go (seq 15956, point 3 of A's list): today A keeps the migration order in a text file and every PR re-chains down_revision by hand. Build: (1) revision ids that cannot collide between parallel PRs (e.g. a timestamp plus slug, created by maity-hub / alembic revision with a fixed template), (2) a tool tools/rechain.py (or a make target) that sets the new migration's down_revision to the current head of origin/main and refuses when more than one new migration is in the branch, (3) a CI check that fails with a clear message when the branch has two Alembic heads against main, telling the author to run the tool. Existing numbered migrations stay as they are (alpha: no renaming churn needed unless trivial). KTW in hub/context with rejected alternatives (hub-side reservation, keep numbers).