The Lantern Under the Mill (SPE-5)

[jakelevirne]

One lantern outlasts a mill. Two rooms, both faces of a new place, mill-race, reached
from the Turning House.

• mill-race:2099-ba — the High Masonry. The working race: black water, the wheel
  turning, an iron nail in a ring of soot with nothing on it.
• mill-race:1099-ba — the Long Noon. Silt, a wheel dry to the hub, brick where the stair
  came down, and the lantern on that same nail. Unlit, and the glass is warm.

The Turning House gains a DOWN exit, the lantern beside its door, and the second stair.
landings is now ["2099 BA", "1099 BA"]. test/engine.test.ts builds its fixture from
the shipped world instead of the lone room, because validateWorld rejects a room whose
exit leaves its world and the House now has one; same start room, same assertions, no
engine change.

Route

turning-house → DOWN → mill-race:2099-ba → FUTURE → mill-race:1099-ba, and back
out by PAST, UP. The 1099 BA room has no spatial exits by design — the stair is brick.

Checks (on this branch)

npm run typecheck                                            # exit 0
npm test                                                     # 36 pass, 0 fail
npm run eval:reach                                           # verdict: PASS  rooms: 3  reachable: 3
node scripts/play.ts --expect mill-race:2099-ba DOWN         # exit 0
node scripts/play.ts --expect mill-race:1099-ba DOWN FUTURE  # exit 0
node scripts/play.ts --expect turning-house DOWN FUTURE PAST UP  # exit 0

Evaluated by SPE-8: verdict: PASS, no failures, every harness route played through the
real engine. Zero fix rounds used.

Trail

• Story: SPE-5 · Plan: SPE-6 (PR Plan: The Lantern Under the Mill (SPE-6) #22) · Generate: SPE-7 (PR Generate: The Lantern Under the Mill — both mill-race rooms #23) · Evaluate: SPE-8
• Outline: design/stories/the-lantern-under-the-mill/OUTLINE.md
• Orchestration log: design/stories/the-lantern-under-the-mill/LOG.md and
  https://linear.app/specfactory/document/orchestration-log-the-lantern-under-the-mill-9549e0d29464