fix(planner): clear the route when waypoints drop below two

Deleting waypoints down to <2 left the last computed route rendered —
nothing cleared the stale geometry (recompute only runs for >=2). Add a
waypoints observer that drops the computed geometry once fewer than two
waypoints remain, via a new clearComputedRoute (keeps the routing
profile, unlike clearRouteData). Covers all delete paths (sidebar, map,
undo).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/planner/app/lib/route-data.test.ts

@@ -6,6 +6,8 @@ import {
   PROFILE_KEY,
   ROAD_METADATA_KEYS,
   clearRouteData,
+  clearComputedRoute,
+  hasComputedRoute,
   extractNoGoAreas,
   getBaseLayer,
   getColorMode,
@@ -266,6 +268,28 @@ describe("clearRouteData", () => {
   });
 });
 
+describe("clearComputedRoute / hasComputedRoute", () => {
+  it("detects computed geometry and clears it while keeping the profile", () => {
+    const { doc, routeData } = createDoc();
+    expect(hasComputedRoute(routeData)).toBe(false);
+
+    writeComputedRoute(doc, routeData, enrichedFixture());
+    setProfile(routeData, "trekking");
+    setColorMode(routeData, "surface");
+    expect(hasComputedRoute(routeData)).toBe(true);
+
+    clearComputedRoute(doc, routeData);
+
+    expect(hasComputedRoute(routeData)).toBe(false);
+    expect(getCoordinates(routeData)).toBeNull();
+    expect(readGeojson(routeData)).toBeUndefined();
+    expect(readRoadMetadata(routeData).surfaces).toEqual([]);
+    // profile (and other prefs) survive — unlike clearRouteData
+    expect(getProfile(routeData)).toBe("trekking");
+    expect(getColorMode(routeData)).toBe("surface");
+  });
+});
+
 describe("extractNoGoAreas", () => {
   it("reads areas and drops degenerate ones", () => {
     const doc = new Y.Doc();

apps/planner/app/lib/route-data.ts

@@ -189,7 +189,12 @@ export function setGeojson(routeData: Y.Map<unknown>, geojson: unknown): void {
 }
 
 /** Removes the computed route and profile (view preferences are kept). */
-export function clearRouteData(doc: Y.Doc, routeData: Y.Map<unknown>): void {
+/**
+ * Clear the computed route geometry + per-coordinate road metadata, but keep
+ * the routing profile. Used when the route can no longer exist (fewer than two
+ * waypoints) so the stale line stops rendering without resetting the profile.
+ */
+export function clearComputedRoute(doc: Y.Doc, routeData: Y.Map<unknown>): void {
   doc.transact(() => {
     routeData.delete("geojson");
     routeData.delete("coordinates");
@@ -198,6 +203,17 @@ export function clearRouteData(doc: Y.Doc, routeData: Y.Map<unknown>): void {
     for (const key of ROAD_METADATA_KEYS) {
       routeData.delete(key);
     }
+  });
+}
+
+/** True if the route data currently holds computed geometry. */
+export function hasComputedRoute(routeData: Y.Map<unknown>): boolean {
+  return routeData.get("coordinates") !== undefined || routeData.get("geojson") !== undefined;
+}
+
+export function clearRouteData(doc: Y.Doc, routeData: Y.Map<unknown>): void {
+  doc.transact(() => {
+    clearComputedRoute(doc, routeData);
     routeData.delete(PROFILE_KEY);
   });
 }

apps/planner/app/lib/use-routing.ts

@@ -15,6 +15,8 @@ import {
   extractNoGoAreas,
   getProfile,
   writeComputedRoute,
+  clearComputedRoute,
+  hasComputedRoute,
 } from "./route-data.ts";
 import { extractWaypoints } from "./waypoint-ymap.ts";
 
@@ -210,11 +212,22 @@ export function useRouting(yjs: YjsState | null, sessionId: string) {
       triggerRecompute();
     };
 
+    // When waypoints drop below two, no route can exist — drop the stale
+    // geometry so the line stops rendering. (Recompute for >=2 is triggered by
+    // the add/move/delete handlers themselves.)
+    const waypointsObserver = () => {
+      if (getWaypointsFromYjs(yjs.waypoints).length < 2 && hasComputedRoute(yjs.routeData)) {
+        clearComputedRoute(yjs.doc, yjs.routeData);
+      }
+    };
+
     yjs.routeData.observe(profileObserver);
     yjs.noGoAreas.observeDeep(noGoObserver);
+    yjs.waypoints.observeDeep(waypointsObserver);
     return () => {
       yjs.routeData.unobserve(profileObserver);
       yjs.noGoAreas.unobserveDeep(noGoObserver);
+      yjs.waypoints.unobserveDeep(waypointsObserver);
     };
   }, [yjs, isHost, requestRoute]);