v0.6.2 — an Extra starts where you put it, a train card is never discarded

Three more from the v0.4.9e gameplay-testing round, filed as Gitea issues, plus two bugs found
underneath them. Gitea#2 is diagnosed but NOT fixed: it needs a ruling, and the reasoning is in
TODO.md under Play Balance.

GITEA#4 — AN EXTRA STARTS WHERE THE PLAYER PUTS IT. Only one Division Point was ever offered,
chosen by number parity. The number no longer decides an Extra's direction — the start does, which
supersedes the recorded ruling that "the number decides, like everything else on the timetable".
The two cannot both hold: an odd, westbound Extra placed at the WEST end would leave the Division
on its first move having crossed nothing, and be paid for the run. Either end now runs the train
away from itself; at an Interchange or a Control Point the player picks the direction. The
Interchange start is a YARD, off the running line, which is what makes the Superintendent clause
work: placing it can never force a collision, a guaranteed one holds it there for another Stage,
and a potential one is the Superintendent's to rule on — exactly evaluateClearance's `blocked` and
`ask`, so nothing new decides collisions. Where an Extra may start is now a house rule
(divisionPointsOnly / ownOffice / anyOffice, defaulting to what the engine already did). The
legacy `atSeat` intent field still replays as it always meant.

FOUND UNDERNEATH IT: an Extra started away from a Division Point ran empty. isBeingMadeUp tested
position alone, so the Control Point start has been shipping since it was added with a train that
could never be given a consist. Found by playing it, not by the tests, which had only asserted
where the tray landed.

FOUND UNDERNEATH IT: collide left the wrecks on the card. Destroyed trains kept their Transit
entries, and evaluateClearance counts every transit as an occupant, so one rear-end collision
permanently poisoned that Mainline card for every later train.

THE MAINLINE CARDS WERE ROLLED, NOT DEALT — drawn from the nine types with replacement, so a
Division could hold two Interchanges and Plains carried the weight of a card printed once. "An
Extra may start at the Interchange if one is on the board" only reads as a rule if the board holds
at most one. Now dealt from the printed deck without replacement, verified over 1600 deals. This
re-deals every seed: the published replays were re-recorded, and the saved games in docs/ are
retired too — two of those were already dead before this release and nobody had noticed.

GITEA#6 — A TRAIN CARD IS NEVER DISCARDED, Timetabled and Extra alike. The forced play needed no
mechanism: nothing discardable plus a hand over the limit leaves exactly one legal way to end the
turn, and playing a train is unconditionally legal, so the corner cannot trap anyone. The bot
needed no rule either. 400/400 games finished, revenue unmoved, trains scheduled 1.2 -> 1.3. The
player is told on the card and on the button.

GITEA#7 — COACH COUNTS. 1/2 Crack Limited 3 -> 2, 5/6 The Sparrow 2 -> 3. A change to the cards,
so Trains3.pdf and the transcription keep the original numbers with a footnote while content.ts
and the Home Deck reference carry what the game plays.

CONTENT.TS COMMENT PASS — no data changed, only comments. Four were factually wrong, including an
office table naming counts doubled long ago and a pointer to a DEALT_DECK_SIZE that has never
existed. Every Enhancement row cited its implementation by line number and every citation had
rotted; they name functions now. Card counts came out of the comments, since they move with play
balance; source-sheet figures and dated measurements stayed.

TODO.md gains an item for a card reference generated from content.ts, in six sections, so the
documentation cannot disagree with the game.

715 tests pass, tsc clean, site builds.

src/engine/state.ts

@@ -354,6 +354,23 @@ export type CrewTray = {
   /** null while a local crew is switching without a train card. */
   trainNumber: number | null;
   trainIsExtra: boolean;
+  /**
+   * STILL BEING ASSEMBLED, somewhere that is not a Division Point.
+   *
+   * `isBeingMadeUp` used to read the position alone — "standing at a Division Point" — which was
+   * true of every train being built when the only place to build one WAS a Division Point. An Extra
+   * may now be started at a Control Point or in an Interchange's yard (§7), and those trains could
+   * not be given a consist at all: they ran empty, and so did every Control Point Extra since that
+   * option was added. Jesse's report says it plainly — an Extra started at the Interchange "would be
+   * loaded with cars".
+   *
+   * Set when such an Extra is placed and cleared the moment it starts running (`enterMainline`), so
+   * it names a train that is being made up rather than one that merely happens to be standing
+   * somewhere. That distinction is load-bearing: a train that ARRIVED at an Office must never be
+   * fillable from the Division Yard, which is the "cars appearing on a train nobody was making up"
+   * bug `isBeingMadeUp` was tightened to kill, and an arriving train never carries this.
+   */
+  beingMadeUp?: boolean;
   /**
    * WHERE THE ENGINE SITS IN THE TRAY, as an index into `consist`.
    *
@@ -470,6 +487,20 @@ export type DivisionNode =
       kind: 'mainline';
       card: MainlineKind;
       transits: Transit[];
+      /**
+       * TRAINS STANDING IN THE INTERCHANGE'S YARD — not out on the running line.
+       *
+       * Only an Interchange ever has these. An Extra started there (§7, Jesse's ruling) is made up
+       * in the yard beside the Mainline, which is why placing it can never be a collision however
+       * busy the card is: it is not on the road yet. It highballs onto this same card at a later
+       * Mainline Phase, through the ordinary §8.1 clearance check — held automatically against a
+       * facing train, put to the Superintendent against a following one — and becomes a `Transit`
+       * at that moment, exactly like a train leaving a Division Point.
+       *
+       * A tray listed here has `position.at === 'mainline'` with this node's index and NO entry in
+       * `transits`. That pair is what distinguishes standing from crossing.
+       */
+      holding?: TrayId[];
       absSignals?: boolean;
       /** Brakeman / Airbrakes / Helpers / Realignment laid on this card. */
       modifiers?: string[];