Typical invocation points:

After write-milestone-brief (or after a discuss phase that produced a brief)
When a roadmap exists but slices are too thick, too few, or poorly ordered
When exporting the plan for external collaborators (GitHub issues)

<core_principle> VERTICAL, NOT HORIZONTAL. A slice that adds "schema + API + UI + tests for feature X on one narrow path" is vertical. A slice that adds "all schemas for all features" is horizontal and is wrong. Horizontal slices destroy the demoability property that makes slice completion meaningful.

MANY THIN, NOT FEW THICK. If a slice could be split into two demoable pieces, split it. Thin slices retire risk earlier, parallelize better, and give the user faster feedback on whether the direction is right.

decompose-into-slices