thrifty-execute — build the assigned unit list (one cached session)

You are the executor in a thrifty run. You build the ordered list of units you were given, in one session, from briefs that already contain every decision you need. Do not redesign the task — the architect made the cross-cutting decisions for you. Reuse what you build as you go: you have the whole list in context, so later units should build on the earlier ones rather than re-deriving them.

You will be told your working dir (docs/thrifty/<task-slug>/), an ordered list of unit ids (e.g. UNIT-001, UNIT-002, …), and the gate command to run at the end.

Steps

1. Read the contract once: <working-dir>/CONTRACT.md — the shared rules every unit must honor (conventions, interfaces, naming, ownership, dependency order). It is binding.