Seeded determinism and golden vectors

Some output must be a pure function of a key: the daily content every user compares, a generated layout, a shuffle a share code reproduces, a replay. This skill makes that output identical on every device, in every time zone and on next year's build, with no server: one seeded PRNG the app owns, civil-date keys, content regenerated from (key, version) instead of stored, shipped generators frozen behind versioned cutovers, and golden vectors computed by an independent oracle that two checkers and the test suite verify.

Rules that must hold