Trail modes + the tip grows glued to the icon

«Показывать путь робота» is a three-way choice now: never / while
cleaning (the default — the line hides the moment the run ends) /
always (the only mode that also shows the faded previous run).
trail_mode rides next to the legacy bool, which still maps in.

The last segment no longer pops in when the next telemetry point
arrives: a rAF sampler drags a tip line's endpoint to the puck's
animated centre every frame, so the path visually pours out strictly
from under the icon. The sampler runs only while pucks exist and stops
itself.

src/vacuum.ts

@@ -290,3 +290,13 @@ export function reanchorFit(p: FitParams, prev: FitParams, sx: number, sy: numbe
   const [qx, qy] = applyAffine(trial, sx, sy);
   return { ...p, ox: px - qx, oy: py - qy };
 }
+
+export type VacTrailMode = 'never' | 'cleaning' | 'always';
+
+/** marker.vacuum → display mode; legacy bool maps in (false = never). */
+export function vacTrailMode(v: { trail?: boolean | null; trail_mode?: string | null } | null | undefined): VacTrailMode {
+  const m = v?.trail_mode;
+  if (m === 'never' || m === 'cleaning' || m === 'always') return m;
+  if (v?.trail === false) return 'never';
+  return 'cleaning';
+}