v0.8.0.5 — the Home Office deck, and lighting the pile a move touched

"Many operations still occurred too fast for me to see", at 10x — where an action
already holds the screen for seven seconds. So it was never duration: a bot drawing
a card changes one number in a panel nobody is watching, and the board sits
unchanged. Raising the dwell was the wrong lever and it had been pulled three
times.

f.deck has carried the face-down count since the Frame existed and nothing drew it
— the display gap test/display-gaps.test.ts sweeps for, surviving in the one panel
that draws every other pile. It is a tile now, first in the row, face down, because
that is the order a card travels and not knowing what is on top is the point.

And the piles a move touched are lit for as long as that move is on screen. Derived
from the frames either side of a step rather than sent, so nothing joins the
protocol and the 0.8.1 board gets it free. What lights follows what is public, and
was measured across four seeds rather than reasoned about: a Home Office draw
lights the deck and never names the card; a Department draw lights that pile, and
the deck too when it refills; a discard lights the Department it lands on; a played
card lights the Salvage Yard. Switching and new trains light nothing here — they
move the board, which the district panel already follows.

A state rather than a flash: the timetable's fixed 1.5s animation would be over
long before a seven-second pause. Not for your own moves.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X6cF1iYvJ1kNmzYBzu4QX6

src/sim/public-delta.ts

@@ -130,3 +130,46 @@ function need<T>(value: T | undefined, what: string): T {
   }
   return value;
 }
+
+/** A face-up or face-down pile a card can move to or from, as the display addresses it. */
+export type PileKey = 'home' | 'salvage' | `dept${number}`;
+
+/**
+ * WHICH PILES A STEP MOVED — derived, never sent.
+ *
+ * The receiver already holds the frame before a step and the frame after it, so which pile changed
+ * is a diff rather than something the wire has to carry. That matters twice over: nothing is added
+ * to the protocol, and it cannot drift out of step with the projection the way a hand-maintained
+ * hint would.
+ *
+ * WHY IT IS NEEDED AT ALL. A player watching somebody else draw a card sees seven seconds of an
+ * unchanged board — the step holds the screen, and the only thing that moved is a number in a panel
+ * they were not looking at. Jesse, playing v0.8.0.4 at 10×: *"many operations still occurred too fast
+ * for me to see"*, which was never about duration. Lighting the pile is what tells the eye where.
+ *
+ * WHAT EACH ACTION MOVES, measured across four seeds rather than reasoned about:
+ *
+ * | intent                  | piles                                                    |
+ * | ----------------------- | -------------------------------------------------------- |
+ * | `draw.fromHomeOffice`   | `home` — the COUNT only; the card itself stays private    |
+ * | `draw.fromDepartment`   | that `dept`, and `home` too when the pile refills from it |
+ * | `card.discard`          | that `dept`                                               |
+ * | `card.play`             | `salvage`, or nothing here when it lands on the board      |
+ * | switching, new trains   | nothing here — those show on the board itself             |
+ */
+export function changedPiles(before: PublicFrame | null, after: PublicFrame): PileKey[] {
+  if (before === null) return [];
+  const out: PileKey[] = [];
+  if (before.deck !== after.deck) out.push('home');
+  after.departmentDepth.forEach((depth, i) => {
+    // The TOP as well as the depth: taking the face-up card and replacing it leaves the count alone
+    // and changes the card everybody can see, which is the half that matters to a watcher.
+    if (before.departmentDepth[i] !== depth || before.departments[i] !== after.departments[i]) {
+      out.push(`dept${i}`);
+    }
+  });
+  if (before.salvage.depth !== after.salvage.depth || before.salvage.top !== after.salvage.top) {
+    out.push('salvage');
+  }
+  return out;
+}