polish(geo): clamp driverLabelFor at '9' instead of wrapping to '0'

src/lib/geo.test.ts

@@ -35,6 +35,17 @@ describe("driverLabelFor", () => {
     expect(driverLabelFor(sorted, sorted[29].id)).toBe("4");
   });
 
+  it("clamps at '9' for the 35th driver and beyond (no '0' wrap)", () => {
+    const drivers = Array.from({ length: 40 }, (_, i) => ({
+      id: `driver-${String(i).padStart(2, "0")}`,
+    }));
+    const sorted = [...drivers].sort((a, b) => a.id.localeCompare(b.id));
+    // Sorted: driver-00 (A) ... driver-34 (9), then driver-35 clamps to "9".
+    expect(driverLabelFor(sorted, sorted[34].id)).toBe("9");
+    expect(driverLabelFor(sorted, sorted[35].id)).toBe("9");
+    expect(driverLabelFor(sorted, sorted[39].id)).toBe("9");
+  });
+
   it("returns '?' for an unknown driver id", () => {
     const drivers = [{ id: "u-1" }];
     expect(driverLabelFor(drivers, "u-missing")).toBe("?");

src/lib/geo.ts

@@ -237,9 +237,10 @@ export function colorForStop(args: {
  * ========================================================================= */
 
 /**
- * Returns the driver label for a given driver id within an alphabetically-
+ * Returns the driver label for a given driver id within an lexically-
  * sorted driver list. Position 0 → "A", 1 → "B", ..., 25 → "Z", 26 → "1",
- * 27 → "2", ... Returns "?" if the id isn't in the list.
+ * 27 → "2", ..., 34 → "9", 35 → "9" (clamped). Returns "?" if the id
+ * isn't in the list.
  *
  * The caller MUST pass a list already sorted by `id` ascending — typically
  * the `driversWithItems` array, which `page.tsx` already sorts by name via
@@ -254,9 +255,12 @@ export function driverLabelFor(
   const idx = sortedDrivers.findIndex((d) => d.id === driverId);
   if (idx === -1) return "?";
   if (idx < 26) return String.fromCharCode("A".charCodeAt(0) + idx);
-  // After Z, fall back to 1..9 (and then loop — at >35 drivers we'll
-  // reuse digits, which is a graceful degradation rather than a crash).
-  return String((idx - 25) % 10);
+  // After Z, fall back to 1..9 and clamp at 9 — the glyph "0" would
+  // read as "unknown driver" next to the existing "?" fallback, and
+  // wrapping back to "1" would alias position 26's driver. Clamping
+  // makes it visually obvious you have >35 drivers without silently
+  // mislabeling anyone.
+  return String(Math.min(idx - 25, 9));
 }
 
 /**