Sequence work into verifiable units

Order work as a sequence of small units, each ending in a state you can check, and don't advance beyond a unit until its declared checks pass. For coupled migrations, invoke /pstack-principle-migrate-callers-then-delete-legacy-apis to define the unit and intermediate gates.

Why: A break caught at the unit that caused it is cheap to localize. A break caught after a batch is buried, and you have already built further on a broken base. Sequencing those same units into a delivery a reviewer can replay turns "trust me" into "watch it go red, then green."

Execution. In a sweep, migration, or any run of similar edits, verify each change at its declared gate before starting dependent work. Each unit is a before/after bracket: known-good state, one change, run the check, then proceed. Use the invoking workflow's verified base, including an integration revision; preserve unrelated work and existing branch ownership. When a lever does the edits, the per-unit check is nearly free. Run it anyway.

Delivery. Stack commits and PRs in the order that proves the work. The canonical shape is the failing test first, then the fix on top. Other story orders are a subtraction before the reshape, a baseline capture before the treatment, the scaffold before the feature. Intermediate proof commits can show red; the checked delivery unit includes the fix. Independently landed units must pass their acceptance gates.

The sequencing complement to the /pstack-principle-prove-it-works, which keeps each check real, and the /pstack-principle-build-the-lever, which makes the per-unit check cheap.