v0.4.9f — an Extra starts where you put it, a train card is never discarded

The 0.6.2 change, ported to the playtest line. Three from the v0.4.9e gameplay-testing round —
Gitea#4 extras did not start where the player said, #6 train cards could be discarded, #7 four
train cards had the wrong coach counts — plus two bugs found underneath #4. Gitea#2 is diagnosed
but NOT fixed; it needs a ruling, and the reasoning is in TODO.md.

GITEA#4 — AN EXTRA STARTS WHERE THE PLAYER PUTS IT. Both Division Points are offered now, and the
START decides the direction rather than the number: an odd westbound Extra placed at the WEST end
would otherwise leave the Division on its first move having crossed nothing and be paid for the
run. 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 an
Extra there can never force a collision, a guaranteed one holds it for another Stage, and a
potential one is the Superintendent's to rule on, which are §8.1's two existing answers. Where an
Extra may start is a new setting in the New Game dialog, defaulting to what the engine already did
so this build does not change under its testers mid-line.

FOUND UNDERNEATH IT, both already shipping: an Extra started away from a Division Point could
never be given a consist and ran empty, so the Control Point start has been broken since it was
added; and collide left destroyed trains' transits on the Mainline card, permanently poisoning
that card for every later train.

THE MAINLINE CARDS ARE DEALT FROM THE PRINTED DECK NOW, without replacement. They were drawn from
the nine types with replacement, so a Division could hold two Interchanges — and "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. This re-deals every seed, so both published replays were retired and re-recorded.

GITEA#6 — A TRAIN CARD IS NEVER DISCARDED, Timetabled and Extra alike. No forcing mechanism was
needed: 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 a hand of four cannot trap anyone. The hand
panel says so on the train, and the blocked end-turn button changes its wording.

GITEA#7 — COACH COUNTS. 1/2 Crack Limited 3 -> 2, 5/6 The Sparrow 2 -> 3.

WHAT DIFFERS FROM THE MAIN LINE. The car-placement round rotation test that accompanies #7 there
arrived with the 0.6 multiplayer work and does not exist here, so there was nothing for the
coach-count change to follow. src/web/main.ts and test/web.test.ts needed hand-resolution: this
line's New Game dialog has neither the mode radios nor the victory dials, so only the Extra-start
parts were taken. The content.ts comment pass came across whole; main's TODO documentation item
did not, since this line keeps its own TODO.

623 tests pass, tsc clean, site builds.

docs/StationMaster-Mainline-Deck-v0.4.5.md

@@ -45,9 +45,13 @@ The PDF art labels this card “Yard”; this reference uses the implementation
 | Trestle | 60 mph. |
 | Interchange | 60 mph. A train may be reordered there only through the card’s printed “sort cars” concept; the current engine does **not** provide a Mainline sorting action for it. |
 
-### PDF/code mismatch requiring correction
+### PDF/code mismatch — CORRECTED
 
-`src/engine/content.ts` defines nine `MAINLINE_PROFILES` types: one Plains entry plus the eight other terrain types above. `setup.ts` selects uniformly from that nine-type list. The second Plains card shown in `Mainline Cards.pdf` is therefore not represented as a duplicate card or as extra Plains weight in setup. If the PDF inventory is authoritative, the setup selection needs a second Plains entry (or an equivalent weighted selection).
+**Was:** `src/engine/content.ts` defines nine `MAINLINE_PROFILES` types: one Plains entry plus the eight other terrain types above. `setup.ts` selected uniformly from that nine-type list, **with replacement**. The second Plains card shown in `Mainline Cards.pdf` was therefore not represented as a duplicate card or as extra Plains weight in setup — and, worse than a weighting error, a Division could be dealt two Interchanges, two Tunnels or two Trestles, none of which the deck contains.
+
+**Now:** `MAINLINE_DECK` in `content.ts` is the inventory table above — ten drawable cards, Plains twice and the other eight once each — and `buildDivision` deals from it without replacement. The two Division Point cards are not in that deck: they are the fixed ends of the Division, laid by `buildDivision` itself rather than drawn.
+
+The Interchange is what forced the correction. §7 lets an Extra be started at the Interchange "if one is on the board" (see `docs/rules/implications.md`, §7), which only reads as a rule if the board can hold at most one.
 
 The executable state represents East and West Division Points as fixed end nodes, not as card records. They are functionally present at the ends of the Division, but are not represented as the two PDF cards in the deck/state model.