Draw freight on the card, and teach the bot to build a railroad

TODO.md

@@ -9,11 +9,44 @@ Ordered within each section by how much it is currently costing us.
 
 ## Next
 
-- [ ] **Find out why switching work does not become Revenue.** The crew now drops 11 cars a game and
-      couples 8 (was 3.3 and ~0.4), at about 4 Moves per productive act — real railroading. Revenue
-      did not move (3.9 → 3.2). Either the freight it is now shuffling is not the freight the
-      industries want, or the loads finish too late in the Day to be worked, or the Revenue is going
-      somewhere and being lost again. Measure the freight chain end to end before changing anything.
+- [ ] **Measure with error bars from now on.** Revenue has a standard deviation of ~9, so a
+      100-game run carries about ±1.0 of noise — every single-change revenue claim in the changelog
+      before the Interlocking work is inside that. Use paired per-seed comparison (the harness deals
+      the same seeds either way) and 400+ games before calling a heuristic change good or bad. The
+      first attempt at the Running Track straight was read as a 0.6 REGRESSION on 100 games and is
+      a 0.7 improvement on 400.
+- [ ] **Confirm the Classification Yard rule against the source.** Cars now return to the Division
+      Yard at the Day boundary — an ASSUMPTION, not a recovered rule. Gap 2c says everything but
+      cabooses goes to Classification and never says how it empties. It is worth +2.32 revenue a
+      game, so if the real rule differs the balance numbers move with it.
+- [x] ~~**Enhancements are placed but mostly do nothing.**~~ Measured: forbidding every Enhancement
+      except Interlocking is worth **-0.01 ± 0.41 (t = -0.04)** over 400 paired seeds. They neither
+      pay nor cost. Left alone. Unlocking the Running Track straight put
+      nine kinds on the board (telegraph 0.73, waterColumn 0.57 …), but only Interlocking has a
+      measured effect. The Telegraph/Telephone/Radio chain adds to the other train's number when
+      dispatching facing trains, which may be worth nothing in solitaire; Water Column removes a
+      Watertower; Facing Point Locks prevents Derail, which is multiplayer-only. Worth measuring
+      what each is actually worth before the bot spends actions on them.
+- [ ] **The marginal Local Operations action is worth ~0, and that is the real ceiling.** Three
+      separate attempts to spend the 60 actions better — capping the draw, pairing the two halves of
+      a load, restricting Enhancements — each measured within noise of zero over 400 paired seeds.
+      76% of the time an outbound industry has neither a stocked green box nor a spotted car, and
+      only 5% of Stages have a single workable facility anywhere, yet redirecting actions at that
+      does nothing. Something upstream limits how much work exists to do at all; find out what
+      before spending more effort on the option mix.
+- [ ] **Freight was stuck at ~2.7 loads a game and three fixes have not moved it.** Sidings,
+      facility placement, car selection and the discarded-load leak all raised revenue (3.2 → 6.5)
+      without raising `loadStarted` past 2.7. The chain is not leaking and the cars are arriving
+      correctly (57% of drops land on a facility that wants them, 0% on one that does not). The
+      binding constraint is now upstream of routing: 60 Local Operations actions a game, and a load
+      needs a stocked green box AND a spotted car AND a free Laborer to line up in the same Stage.
+      Measure how many Stages have all three before changing any heuristic — the answer may be that
+      the economy, not the bot, is what caps freight.
+- [ ] **`stats.ts` undercounts freight.** `rev.freightUnload` is assigned `eventCounts['unloadBegan']`
+      — unloads *begun*, not revenue *earned* — and `grossFreight` uses `freightLoad` alone, so
+      `freightShare` omits unload revenue entirely. The comment justifying it ("an unload scores
+      through the same event as a load completion") is wrong: `apply.ts:947` emits a distinct
+      `freightUnload` reason. This is why freight was recorded at 13–18% of gross.
 
 ---
 
@@ -45,13 +78,16 @@ target is settled and freight carries its intended share.
       of an unwinnable opening deal. Blunt: it lifts the whole ladder and dilutes every other
       category. The better answer may be fewer Terminals, a cheaper first upgrade, or more A/D
       capacity at the Whistle Post itself.
-- [ ] **Industry density** (9 → 27, Gap 12). Restored roughly the prototype ratio; freight still only
-      13–18% of gross revenue.
+- [ ] **Industry density** (9 → 27, Gap 12). Restored roughly the prototype ratio. The "freight is
+      only 13–18% of gross" figure that motivated this was partly a measurement bug (see the
+      `stats.ts` item) and partly the car-selection bug; freight now runs at 37%. Worth re-deciding
+      whether 27 is still the right number now that the industries are actually served.
 - [ ] **Train density.** Left alone by decision, but noted: 22 train cards in 140 are drawn less often
       than 22 in 115 were, and trains scheduled fell 2.9 → 2.1 as a side effect of the other density
       changes.
-- [ ] **The victory target itself** (20 over 5 Days). Still only 1 win in 100. Worth revisiting once
-      the bot exploits sidings, since that is a known unclaimed gain.
+- [ ] **The victory target itself** (20 over 5 Days). 5 wins in 100, up from 1, and the bot now does
+      exploit sidings — so that unclaimed gain has been claimed and the target is still missed by a
+      wide margin (mean 6.0 against 20). This is the next real balance question.
 
 ---
 
@@ -84,6 +120,42 @@ target is settled and freight carries its intended share.
 
 ## Done, kept for the reasoning
 
+- [x] **Put rolling stock back into circulation.** The Classification Yard was write-only — seven
+      writers, no readers — so 37% of all rolling stock left the game by Day 5. Returning it at the
+      Day boundary is **+2.32 ± 0.52 (t = 8.79)**, the largest single change measured on this bot,
+      and it was ranked THIRD and predicted not to matter because the Division Yard never runs dry.
+      The aggregate was the wrong measure; having the right commodity at the right moment is what
+      counts.
+- [x] **Make Enhancements reachable at all.** The bot never laid a straight on the Running Track
+      (0.00 in 100 games) because two-arc run-arounds do not need one — so 13 of the 18 Enhancement
+      cards had nowhere to go, including Interlocking, the only cure for the only penalty in the
+      game (`no free A/D track`, 27% of gross). One scored straight fixed it: enhancements placed
+      0.64 → 3.01, collision cost 2.70 → 1.91, worst game −47 → −24. Revenue +0.70 ± 0.74 paired
+      over 400 seeds — real but not significant alone; the variance reduction is the clearer win.
+- [x] **Stop the bot discarding its own freight.** `canStockProductively` did not check the Division
+      Yard while the engine's `stockOutbound` does, so Freight Agent was chosen when nothing could be
+      stocked and the follow-through fell through to an unjam that threw a waiting load out of the
+      green box — 3.10 a game against 2.71 started. Now 0.00. Revenue 6.0 → 6.5, wins 5 → 8 in 100.
+      Also confirmed **routing was never the problem**: 0% of drops land on a facility that does not
+      want the car.
+- [x] **Why switching work did not become Revenue.** Answered: it was the freight the crew shuffled,
+      not the shuffling. The chain never leaked — 95% of started loads finished — it was barely
+      entered, because a load needs a matching empty car spotted and half the industries never asked
+      for one. Three fixes later (sidings, facility placement, car selection) revenue is 3.2 → 6.0
+      and freight 26% → 37% of gross.
+- [x] **Fix car selection.** Three of six industries were invisible to `wantedCars` — a hand-written
+      industry→car map naming two industries that do not exist and omitting three that do — so tank
+      cars were dropped **0 times in 100 games**. Derived from `INDUSTRY_PROFILES` now, and the
+      second commodity of the two-commodity industries is reachable. Revenue 5.0 → 6.0, freight
+      share 25% → 37%, wins 1 → 5 in 100.
+- [x] **Put the industries on the run-around.** Facility placement was unscored — the first legal
+      square — so 0.00 facilities a game sat on a loop; now 1.08. The instructive part was the
+      second bug: scoring facilities onto the siding row dropped run-arounds 91→36, because the
+      anchor test asked a card's KIND rather than its PORTS and an industry in the line read as a
+      dead end. Revenue 4.1 → 5.0. Freight did **not** follow, which is the item above.
+- [x] **Make the bot build sidings that are sidings.** 0 run-arounds in 100 games → 91. Three bugs,
+      all scoring on local shape without checking it reached anything; the decisive one was that
+      `bestTrackLay` never declined a piece, so it spent the track supply on whatever was legal.
 - [x] **Teach the bot what a siding is for.** Nose coupling (§A.3) implemented, so approach direction
       decides which car is droppable; the bot runs around rather than setting out, when the drop can
       follow. Switching activity transformed, revenue unchanged.