v0.4.9h — a leg that is part of the row, the deck the sheet prints, and regions not miles per hour

The 0.4.9 line's port of v0.7.2, minus Gitea#18: the Division map redraw is a
multiplayer redesign and does not belong in a build people are mid-playtest on.

Gitea#17 — a 45° leg is an end of the west-to-east row, so backing into a cut
through a curve's south leg no longer couples it back to front, and a crew
pulling out through a leg takes its own cut with it.

Gitea#14 — every count is docs/Deck cards5.xlsx, including removing the Q12
office doubling and the Gap 12 industry tripling.

Gitea#15 — RAR reversed it: the placement is legal; what must hold is that no
train crosses the gap.

Gitea#3 — the printed speeds are scenery. One Stage per printed region, and
where a train starts is what varies.

test/harness.test.ts

@@ -226,14 +226,28 @@ describe('the game conserves Rolling Stock', () => {
       for (let t = 0; t < 50_000; t++) {
         const before = census(s);
         const pumped = pump(s);
-        // §10 — a collision destroys both trains and everything they were carrying. That is the one
-        // legitimate way the count falls, so the expectation follows it down.
-        for (const e of pumped) {
-          if (e.type === 'trainsDestroyed') for (const tr of e.trains) expected -= tr.consist.length;
-        }
-        assert.ok(
-          census(s) === before || pumped.some((e) => e.type === 'trainsDestroyed'),
-          `seed ${seed}: the engine changed the census by ${census(s) - before} outside a collision`,
+        /**
+         * A COLLISION DESTROYS NO CAR, and this used to assume it destroyed all of them.
+         *
+         * The subtraction that stood here — `expected -= tr.consist.length` for every train in a
+         * `trainsDestroyed` event — describes a rule the engine does not have. Gap 2c (`advance.ts`,
+         * "TAKE THE WRECK OFF THE CARD") sends the wreck's cabooses back to the Division Yard and
+         * everything else to Classification, so the stock is conserved through a collision like any
+         * other move. The train is destroyed; its cars are not.
+         *
+         * It passed for as long as it did because none of the six seeds below ever collided, so the
+         * branch never ran. Changing the deck to the sheet's counts (Gitea#14) moved the deals, seed
+         * 24757 collided, and the test failed claiming the engine had CONJURED three cars — the
+         * exact opposite of what had happened.
+         *
+         * So the census is now held flat, unconditionally, which is both the real invariant and a
+         * stronger test than the one it replaces: there is no longer any event that excuses a
+         * change, and `expected` cannot drift away from the supply it was dealt.
+         */
+        assert.equal(
+          census(s),
+          before,
+          `seed ${seed}: the engine changed the census by ${census(s) - before} while pumping`,
         );
         if (s.status === 'finished') break;
         const actor = s.clock.pendingDecision !== null ? s.clock.superintendent : s.clock.currentActor;