feat(GRO-2156): travel buffer + reorder endpoint (Phase 2.2)

- Apply travel buffer between consecutive stops (default 15 / businessSettings.defaultTravelBufferMins); first stop carries bufferMins 0
- detectScheduleConflicts: flag tight schedule when appointment gap < travelMins + bufferMins; never auto-move appointments
- PATCH /api/routes/:routeId/reorder — validate permutation of current stops, persist new stopOrder (two-pass to avoid unique collision), re-estimate legs, re-apply buffers, recompute totals
- Return route + per-stop conflict flags + hasConflicts/conflictCount on /daily, /optimize, /reorder
- Unit tests for detectScheduleConflicts + recomputeLegsForOrder; UAT_PLAYBOOK §4.17

Co-Authored-By: Paperclip <noreply@paperclip.ing>

UAT_PLAYBOOK.md

@@ -366,7 +366,7 @@ A groomer's daily route is one row per `(staffId, routeDate)` in `groomer_routes
 | # | Scenario | Steps | Expected |
 |---|----------|-------|----------|
 | TC-API-16.1 | Fetch daily route (auto-create draft) | As **manager**, `GET /api/routes/daily?staffId={groomerId}&date=YYYY-MM-DD` for a date with no existing route | 200 OK; body `{ route, stops }`. `route.status` is `"draft"`, `route.staffId`/`routeDate` match, `stops` is `[]`. Re-calling returns the same route row (no duplicate) |
-| TC-API-16.2 | Optimize a multi-stop day | As manager, with ≥2 geocoded appointments for the groomer on the date, `POST /api/routes/optimize` body `{ "staffId": "{groomerId}", "date": "YYYY-MM-DD" }` | 200 OK; `route.status: "optimized"`, `optimizedAt` set, `totalTravelMins`/`totalDistanceKm` populated. `stops` ordered by `stopOrder` (1..N); first stop has `travelMinsFromPrev: null`, the rest positive. `provider` is `"nearest_neighbor"` (no Google key in UAT). Each stop carries `bufferMins` (default 15) |
+| TC-API-16.2 | Optimize a multi-stop day | As manager, with ≥2 geocoded appointments for the groomer on the date, `POST /api/routes/optimize` body `{ "staffId": "{groomerId}", "date": "YYYY-MM-DD" }` | 200 OK; `route.status: "optimized"`, `optimizedAt` set, `totalTravelMins`/`totalDistanceKm` populated. `stops` ordered by `stopOrder` (1..N); first stop has `travelMinsFromPrev: null`, the rest positive. `provider` is `"nearest_neighbor"` (no Google key in UAT). The first stop carries `bufferMins: 0` (no predecessor); every later stop carries `bufferMins` = `businessSettings.defaultTravelBufferMins` (default 15). Response also includes `hasConflicts` / `conflictCount` and each stop a `conflict` object (GRO-2156, see §4.17) |
 | TC-API-16.3 | Re-optimize replaces prior order | As manager, run TC-API-16.2 twice | Second call returns 200; stops fully replaced (no duplicate `route_stops`, `stopOrder` still contiguous 1..N), `optimizedAt` refreshed |
 | TC-API-16.4 | Skips un-geocoded appointments | As manager, optimize a day where one appointment's client has no coordinates | 200 OK; that appointment is absent from `stops` and listed under `skipped[]` with `reason: "client address is not geocoded"`; a corresponding entry appears in `warnings[]` |
 | TC-API-16.5 | Empty / single-stop day | As manager, optimize a date with 0 (or 1) geocoded appointments | 200 OK; `route.status: "optimized"`, `totalTravelMins: 0`, `totalDistanceKm: "0.00"`. For 1 stop, `stops` has one entry with `travelMinsFromPrev: null` |
@@ -377,6 +377,28 @@ A groomer's daily route is one row per `(staffId, routeDate)` in `groomer_routes
 | TC-API-16.10 | Manager must supply staffId | As manager, `POST /api/routes/optimize` body `{ "date": "YYYY-MM-DD" }` (no staffId) | 400 `{ error: "staffId is required" }` |
 | TC-API-16.11 | Invalid date rejected | `GET /api/routes/daily?staffId=...&date=06-08-2026` (wrong format) | 400 validation error (`date must be YYYY-MM-DD`) |
 
+### 4.17 Route Optimization — Travel Buffer + Reorder (GRO-2156, Phase 2.2)
+
+Builds on §4.16. After optimization each consecutive leg carries a travel `bufferMins` (= `businessSettings.defaultTravelBufferMins`, default 15; the first stop is `0`). The API derives a per-stop **`conflict`** object at read time on `GET /api/routes/daily`, `POST /api/routes/optimize`, and `PATCH /api/routes/:routeId/reorder`:
+
+- `conflict.scheduleGapMins` — minutes between the previous appointment's `endTime` and this appointment's `startTime` (null for the first stop)
+- `conflict.requiredGapMins` — `travelMinsFromPrev + bufferMins` (null for the first stop)
+- `conflict.shortfallMins` — `requiredGapMins − scheduleGapMins` (positive ⇒ tight)
+- `conflict.hasConflict` — true when `shortfallMins > 0` ("tight schedule"); appointments are **never auto-moved**, only flagged
+
+`PATCH /api/routes/:routeId/reorder` accepts `{ "stopOrder": ["<routeStopId>", …] }` (every current stop id, exactly once, first-to-last), persists the new `stopOrder`, re-estimates each leg's travel offline for the new adjacency, re-applies buffers, recomputes route totals, and returns the route with refreshed conflict flags. **Auth: manager (any route) or groomer (own route only).**
+
+| ID | Scenario | Steps | Expected |
+|----|----------|-------|----------|
+| TC-API-17.1 | Conflict flags on optimize | As manager, optimize a day with ≥2 geocoded appointments whose times are close together | 200 OK; top-level `hasConflicts` (bool) + `conflictCount` (int). First stop `conflict.hasConflict:false` with null gap fields. A later stop whose `scheduleGapMins < travelMinsFromPrev + bufferMins` has `conflict.hasConflict:true` and positive `shortfallMins` |
+| TC-API-17.2 | No false conflict on a roomy schedule | Optimize a day where appointment gaps comfortably exceed travel + buffer | 200 OK; `hasConflicts:false`, `conflictCount:0`, every `conflict.shortfallMins ≤ 0` |
+| TC-API-17.3 | Reorder persists new order | As manager, take an optimized route, `PATCH /api/routes/{routeId}/reorder` with the stop ids in a new order | 200 OK; `stops` returned in the requested order with contiguous `stopOrder` 1..N; first stop `travelMinsFromPrev:null`/`bufferMins:0`, others recomputed; `route.totalTravelMins`/`totalDistanceKm` updated |
+| TC-API-17.4 | Reorder re-flags conflicts | Reorder so a far-apart pair becomes adjacent | 200 OK; `conflict` flags recomputed for the new adjacency (`hasConflicts`/`conflictCount` reflect the new order) |
+| TC-API-17.5 | Reorder validation — wrong stop set | `PATCH …/reorder` with a missing, extra, duplicate, or unknown stop id | 400 with an explanatory `error` (e.g. "must list every stop exactly once", "unknown stop id", "duplicate stop id") |
+| TC-API-17.6 | Reorder unknown route | `PATCH /api/routes/{randomUuid}/reorder` with any body | 404 `{ error: "Route not found" }` |
+| TC-API-17.7 | Reorder invalid routeId | `PATCH /api/routes/not-a-uuid/reorder` | 400 `{ error: "routeId must be a UUID" }` |
+| TC-API-17.8 | Groomer cannot reorder another's route | As groomer, reorder a route owned by a different groomer | 403 Forbidden (`groomers may only access their own route`) |
+
 ## Pass/Fail Criteria
 
 **Pass:**

src/__tests__/routeOptimization.test.ts

@@ -4,6 +4,8 @@ import {
   estimateLeg,
   nearestNeighborOrder,
   optimizeRoute,
+  detectScheduleConflicts,
+  recomputeLegsForOrder,
   MAX_STOPS_PER_ROUTE,
   type RouteStopInput,
 } from "../services/routeOptimization.js";
@@ -182,3 +184,152 @@ describe("optimizeRoute — >25 stop chunking", () => {
     expect(new Set(r.stops.map((s) => s.appointmentId)).size).toBe(stops.length);
   });
 });
+
+describe("detectScheduleConflicts", () => {
+  const at = (iso: string) => new Date(iso);
+
+  it("returns no conflict and null gaps for an empty or single-stop route", () => {
+    expect(detectScheduleConflicts([])).toEqual([]);
+    const one = detectScheduleConflicts([
+      {
+        appointmentStartTime: at("2026-06-08T09:00:00Z"),
+        appointmentEndTime: at("2026-06-08T10:00:00Z"),
+        travelMinsFromPrev: null,
+        bufferMins: 15,
+      },
+    ]);
+    expect(one).toEqual([
+      {
+        hasConflict: false,
+        scheduleGapMins: null,
+        requiredGapMins: null,
+        shortfallMins: null,
+      },
+    ]);
+  });
+
+  it("flags a tight schedule when gap < travel + buffer", () => {
+    // Stop 1 ends 10:00, stop 2 starts 10:20 → 20min gap. Travel 15 + buffer 15
+    // = 30 required → shortfall 10 → conflict.
+    const flags = detectScheduleConflicts([
+      {
+        appointmentStartTime: at("2026-06-08T09:00:00Z"),
+        appointmentEndTime: at("2026-06-08T10:00:00Z"),
+        travelMinsFromPrev: null,
+        bufferMins: 0,
+      },
+      {
+        appointmentStartTime: at("2026-06-08T10:20:00Z"),
+        appointmentEndTime: at("2026-06-08T11:00:00Z"),
+        travelMinsFromPrev: 15,
+        bufferMins: 15,
+      },
+    ]);
+    expect(flags[0]!.hasConflict).toBe(false);
+    expect(flags[1]).toEqual({
+      hasConflict: true,
+      scheduleGapMins: 20,
+      requiredGapMins: 30,
+      shortfallMins: 10,
+    });
+  });
+
+  it("does not flag when the gap comfortably covers travel + buffer", () => {
+    // 90min gap, 15 travel + 15 buffer = 30 required → 60 slack → no conflict.
+    const flags = detectScheduleConflicts([
+      {
+        appointmentStartTime: at("2026-06-08T09:00:00Z"),
+        appointmentEndTime: at("2026-06-08T10:00:00Z"),
+        travelMinsFromPrev: null,
+        bufferMins: 0,
+      },
+      {
+        appointmentStartTime: at("2026-06-08T11:30:00Z"),
+        appointmentEndTime: at("2026-06-08T12:00:00Z"),
+        travelMinsFromPrev: 15,
+        bufferMins: 15,
+      },
+    ]);
+    expect(flags[1]).toEqual({
+      hasConflict: false,
+      scheduleGapMins: 90,
+      requiredGapMins: 30,
+      shortfallMins: -60,
+    });
+  });
+
+  it("treats a null travelMinsFromPrev as zero travel", () => {
+    const flags = detectScheduleConflicts([
+      {
+        appointmentStartTime: at("2026-06-08T09:00:00Z"),
+        appointmentEndTime: at("2026-06-08T10:00:00Z"),
+        travelMinsFromPrev: null,
+        bufferMins: 0,
+      },
+      {
+        appointmentStartTime: at("2026-06-08T10:05:00Z"),
+        appointmentEndTime: at("2026-06-08T11:00:00Z"),
+        travelMinsFromPrev: null,
+        bufferMins: 15,
+      },
+    ]);
+    // 5min gap vs 0 travel + 15 buffer = 15 required → conflict, shortfall 10.
+    expect(flags[1]!.hasConflict).toBe(true);
+    expect(flags[1]!.requiredGapMins).toBe(15);
+    expect(flags[1]!.shortfallMins).toBe(10);
+  });
+
+  it("flags overlapping appointments (negative gap) as conflicts", () => {
+    const flags = detectScheduleConflicts([
+      {
+        appointmentStartTime: at("2026-06-08T09:00:00Z"),
+        appointmentEndTime: at("2026-06-08T10:00:00Z"),
+        travelMinsFromPrev: null,
+        bufferMins: 0,
+      },
+      {
+        appointmentStartTime: at("2026-06-08T09:30:00Z"),
+        appointmentEndTime: at("2026-06-08T10:30:00Z"),
+        travelMinsFromPrev: 10,
+        bufferMins: 15,
+      },
+    ]);
+    expect(flags[1]!.scheduleGapMins).toBe(-30);
+    expect(flags[1]!.hasConflict).toBe(true);
+    expect(flags[1]!.shortfallMins).toBe(55);
+  });
+});
+
+describe("recomputeLegsForOrder", () => {
+  it("returns null travel for an empty or single-point order", () => {
+    expect(recomputeLegsForOrder([])).toEqual([]);
+    expect(recomputeLegsForOrder([{ latitude: 40, longitude: -74 }])).toEqual([
+      { travelMinsFromPrev: null, travelDistanceKmFromPrev: null },
+    ]);
+  });
+
+  it("estimates each leg for the fixed given order without reordering", () => {
+    const pts = [
+      { latitude: 0, longitude: 0 },
+      { latitude: 0, longitude: 1 },
+      { latitude: 0, longitude: 2 },
+    ];
+    const legs = recomputeLegsForOrder(pts);
+    expect(legs).toHaveLength(3);
+    expect(legs[0]).toEqual({
+      travelMinsFromPrev: null,
+      travelDistanceKmFromPrev: null,
+    });
+    // Each leg equals estimateLeg between adjacent points (no optimization).
+    const e01 = estimateLeg(pts[0]!, pts[1]!);
+    const e12 = estimateLeg(pts[1]!, pts[2]!);
+    expect(legs[1]).toEqual({
+      travelMinsFromPrev: e01.mins,
+      travelDistanceKmFromPrev: e01.distanceKm,
+    });
+    expect(legs[2]).toEqual({
+      travelMinsFromPrev: e12.mins,
+      travelDistanceKmFromPrev: e12.distanceKm,
+    });
+  });
+});

src/routes/routes.ts

@@ -19,7 +19,10 @@ import type { AppEnv, StaffRow } from "../middleware/rbac.js";
 import {
   optimizeRoute,
   resolveRouteGoogleApiKey,
+  detectScheduleConflicts,
+  recomputeLegsForOrder,
   type RouteStopInput,
+  type StopConflictFlags,
 } from "../services/routeOptimization.js";
 
 export const routesRouter = new Hono<AppEnv>();
@@ -34,6 +37,11 @@ const optimizeBodySchema = z.object({
   date: z.string().regex(/^\d{4}-\d{2}-\d{2}$/, "date must be YYYY-MM-DD"),
 });
 
+const reorderBodySchema = z.object({
+  // New visiting order expressed as routeStops.id values, first-to-last.
+  stopOrder: z.array(z.string().uuid()).min(1),
+});
+
 /**
  * Resolves the target staffId for the request and enforces the groomer-own /
  * manager authorization rule. Groomers may only act on their own route; if a
@@ -96,6 +104,31 @@ async function loadRouteStops(db: ReturnType<typeof getDb>, routeId: string) {
     .orderBy(asc(routeStops.stopOrder));
 }
 
+type LoadedRouteStop = Awaited<ReturnType<typeof loadRouteStops>>[number];
+
+/**
+ * Annotates persisted stops with "tight schedule" conflict flags for the
+ * frontend. Conflicts are derived at read time from the live appointment times,
+ * persisted travel estimates and buffers — never auto-resolved by moving stops.
+ */
+function annotateConflicts(stops: LoadedRouteStop[]): {
+  stops: Array<LoadedRouteStop & { conflict: StopConflictFlags }>;
+  hasConflicts: boolean;
+  conflictCount: number;
+} {
+  const flags = detectScheduleConflicts(
+    stops.map((s) => ({
+      appointmentStartTime: s.appointmentStartTime,
+      appointmentEndTime: s.appointmentEndTime,
+      travelMinsFromPrev: s.travelMinsFromPrev,
+      bufferMins: s.bufferMins,
+    }))
+  );
+  const annotated = stops.map((s, i) => ({ ...s, conflict: flags[i]! }));
+  const conflictCount = flags.filter((f) => f.hasConflict).length;
+  return { stops: annotated, hasConflicts: conflictCount > 0, conflictCount };
+}
+
 /**
  * GET /api/routes/daily?staffId=&date=
  * Fetches (creating a draft if absent) the daily route for a groomer, with all
@@ -130,7 +163,13 @@ routesRouter.get("/daily", zValidator("query", dailyQuerySchema), async (c) => {
   }
 
   const stops = await loadRouteStops(db, route!.id);
-  return c.json({ route, stops });
+  const annotated = annotateConflicts(stops);
+  return c.json({
+    route,
+    stops: annotated.stops,
+    hasConflicts: annotated.hasConflicts,
+    conflictCount: annotated.conflictCount,
+  });
 });
 
 /**
@@ -262,7 +301,9 @@ routesRouter.post(
               s.travelDistanceKmFromPrev == null
                 ? null
                 : s.travelDistanceKmFromPrev.toFixed(2),
-            bufferMins,
+            // Buffer applies between consecutive stops; the first stop has no
+            // predecessor, so it carries no travel buffer.
+            bufferMins: i === 0 ? 0 : bufferMins,
           }))
         );
       }
@@ -271,9 +312,12 @@ routesRouter.post(
     });
 
     const stops = await loadRouteStops(db, route.id);
+    const annotated = annotateConflicts(stops);
     return c.json({
       route,
-      stops,
+      stops: annotated.stops,
+      hasConflicts: annotated.hasConflicts,
+      conflictCount: annotated.conflictCount,
       provider: optimized.provider,
       chunked: optimized.chunked,
       subRouteCount: optimized.subRouteCount,
@@ -282,3 +326,137 @@ routesRouter.post(
     });
   }
 );
+
+/**
+ * PATCH /api/routes/:routeId/reorder  { stopOrder: string[] }
+ * Persists a manual stop order (array of routeStops.id, first-to-last), then
+ * re-runs the buffer logic: each leg's travel is re-estimated for the new
+ * adjacency, the default travel buffer is re-applied between consecutive stops,
+ * route totals are recomputed, and tight-schedule conflicts are re-flagged.
+ * Appointments are never moved. Auth: groomer (own route) or manager.
+ */
+routesRouter.patch(
+  "/:routeId/reorder",
+  zValidator("json", reorderBodySchema),
+  async (c) => {
+    const db = getDb();
+    const routeId = c.req.param("routeId");
+    if (!z.string().uuid().safeParse(routeId).success) {
+      return c.json({ error: "routeId must be a UUID" }, 400);
+    }
+    const { stopOrder: newOrderIds } = c.req.valid("json");
+
+    const [route] = await db
+      .select()
+      .from(groomerRoutes)
+      .where(eq(groomerRoutes.id, routeId));
+    if (!route) {
+      return c.json({ error: "Route not found" }, 404);
+    }
+
+    // Reuse the groomer-own / manager authorization rule against the route owner.
+    const resolved = resolveTargetStaffId(c.get("staff"), route.staffId);
+    if ("error" in resolved) {
+      return c.json({ error: resolved.error }, resolved.status);
+    }
+
+    const existing = await db
+      .select({
+        id: routeStops.id,
+        latitude: routeStops.latitude,
+        longitude: routeStops.longitude,
+      })
+      .from(routeStops)
+      .where(eq(routeStops.routeId, routeId));
+
+    // The new order must be an exact permutation of the route's current stops.
+    const existingIds = new Set(existing.map((s) => s.id));
+    if (newOrderIds.length !== existing.length) {
+      return c.json(
+        {
+          error: `stopOrder must list every stop exactly once (expected ${existing.length}, got ${newOrderIds.length})`,
+        },
+        400
+      );
+    }
+    const seen = new Set<string>();
+    for (const id of newOrderIds) {
+      if (!existingIds.has(id)) {
+        return c.json({ error: `unknown stop id: ${id}` }, 400);
+      }
+      if (seen.has(id)) {
+        return c.json({ error: `duplicate stop id: ${id}` }, 400);
+      }
+      seen.add(id);
+    }
+
+    const [settings] = await db.select().from(businessSettings).limit(1);
+    const bufferMins = settings?.defaultTravelBufferMins ?? 15;
+
+    const byId = new Map(existing.map((s) => [s.id, s]));
+    const legs = recomputeLegsForOrder(
+      newOrderIds.map((id) => {
+        const s = byId.get(id)!;
+        return { latitude: s.latitude, longitude: s.longitude };
+      })
+    );
+
+    const totalTravelMins = legs.reduce(
+      (sum, l) => sum + (l.travelMinsFromPrev ?? 0),
+      0
+    );
+    const totalDistanceKm =
+      Math.round(
+        legs.reduce((sum, l) => sum + (l.travelDistanceKmFromPrev ?? 0), 0) * 100
+      ) / 100;
+
+    const now = new Date();
+    await db.transaction(async (tx) => {
+      // Two-pass update: park stopOrder in a non-colliding negative range first
+      // so the unique(routeId, stopOrder) constraint never trips mid-reorder.
+      for (let i = 0; i < newOrderIds.length; i++) {
+        await tx
+          .update(routeStops)
+          .set({ stopOrder: -(i + 1), updatedAt: now })
+          .where(eq(routeStops.id, newOrderIds[i]!));
+      }
+      for (let i = 0; i < newOrderIds.length; i++) {
+        const leg = legs[i]!;
+        await tx
+          .update(routeStops)
+          .set({
+            stopOrder: i + 1,
+            travelMinsFromPrev: leg.travelMinsFromPrev,
+            travelDistanceKmFromPrev:
+              leg.travelDistanceKmFromPrev == null
+                ? null
+                : leg.travelDistanceKmFromPrev.toFixed(2),
+            bufferMins: i === 0 ? 0 : bufferMins,
+            updatedAt: now,
+          })
+          .where(eq(routeStops.id, newOrderIds[i]!));
+      }
+      await tx
+        .update(groomerRoutes)
+        .set({
+          totalTravelMins,
+          totalDistanceKm: totalDistanceKm.toFixed(2),
+          updatedAt: now,
+        })
+        .where(eq(groomerRoutes.id, routeId));
+    });
+
+    const [updatedRoute] = await db
+      .select()
+      .from(groomerRoutes)
+      .where(eq(groomerRoutes.id, routeId));
+    const stops = await loadRouteStops(db, routeId);
+    const annotated = annotateConflicts(stops);
+    return c.json({
+      route: updatedRoute,
+      stops: annotated.stops,
+      hasConflicts: annotated.hasConflicts,
+      conflictCount: annotated.conflictCount,
+    });
+  }
+);

src/services/routeOptimization.ts

@@ -411,3 +411,103 @@ export async function resolveRouteGoogleApiKey(
   const fromEnv = process.env.GOOGLE_MAPS_API_KEY?.trim();
   return fromEnv ? fromEnv : null;
 }
+
+// ─── Travel buffer & schedule-conflict logic (GRO-2156, Phase 2.2) ───────────
+
+/** A single stop's timing inputs for schedule-conflict detection. */
+export interface ScheduleStopTiming {
+  /** Scheduled appointment start. */
+  appointmentStartTime: Date;
+  /** Scheduled appointment end. */
+  appointmentEndTime: Date;
+  /** Travel minutes into this stop from the previous one (null for first). */
+  travelMinsFromPrev: number | null;
+  /** Configured buffer minutes before this stop. */
+  bufferMins: number;
+}
+
+/** Conflict annotation for one stop, surfaced for the frontend to display. */
+export interface StopConflictFlags {
+  /** True when the schedule gap is too tight for travel + buffer. */
+  hasConflict: boolean;
+  /** Minutes between the previous appointment's end and this one's start.
+   * Null for the first stop (no predecessor). */
+  scheduleGapMins: number | null;
+  /** travelMinsFromPrev + bufferMins. Null for the first stop. */
+  requiredGapMins: number | null;
+  /** requiredGapMins − scheduleGapMins; positive when the schedule is tight.
+   * Null for the first stop. */
+  shortfallMins: number | null;
+}
+
+const MS_PER_MIN = 60_000;
+
+/**
+ * Detects "tight schedule" conflicts between consecutive stops, in visiting
+ * order. A conflict exists when the real gap between the previous appointment's
+ * end and this appointment's start is smaller than the time needed to travel
+ * plus the configured buffer (`travelMinsFromPrev + bufferMins`).
+ *
+ * This only *flags* conflicts — appointments are never moved. The first stop
+ * has no predecessor and is therefore always conflict-free.
+ */
+export function detectScheduleConflicts(
+  stops: ScheduleStopTiming[]
+): StopConflictFlags[] {
+  return stops.map((s, i) => {
+    if (i === 0) {
+      return {
+        hasConflict: false,
+        scheduleGapMins: null,
+        requiredGapMins: null,
+        shortfallMins: null,
+      };
+    }
+    const prev = stops[i - 1]!;
+    const scheduleGapMins = Math.round(
+      (s.appointmentStartTime.getTime() - prev.appointmentEndTime.getTime()) /
+        MS_PER_MIN
+    );
+    const requiredGapMins = (s.travelMinsFromPrev ?? 0) + s.bufferMins;
+    const shortfallMins = requiredGapMins - scheduleGapMins;
+    return {
+      hasConflict: shortfallMins > 0,
+      scheduleGapMins,
+      requiredGapMins,
+      shortfallMins,
+    };
+  });
+}
+
+/** A coordinate used when recomputing legs for a fixed (manually chosen) order. */
+export interface OrderedPoint {
+  latitude: number;
+  longitude: number;
+}
+
+/** Recomputed per-leg travel for a fixed stop order. */
+export interface RecomputedLeg {
+  /** Null for the first stop. */
+  travelMinsFromPrev: number | null;
+  /** Null for the first stop. Kilometres, 2-dp. */
+  travelDistanceKmFromPrev: number | null;
+}
+
+/**
+ * Recomputes per-leg travel estimates for a *fixed* visiting order (e.g. after a
+ * manual reorder). Unlike {@link optimizeRoute} this does not reorder anything —
+ * it walks the given order and estimates each leg offline via {@link estimateLeg}
+ * so a manual drag does not consume Google Directions quota.
+ */
+export function recomputeLegsForOrder(points: OrderedPoint[]): RecomputedLeg[] {
+  return points.map((p, i) => {
+    if (i === 0) {
+      return { travelMinsFromPrev: null, travelDistanceKmFromPrev: null };
+    }
+    const est = estimateLeg(points[i - 1]!, p);
+    return {
+      travelMinsFromPrev: est.mins,
+      travelDistanceKmFromPrev: est.distanceKm,
+    };
+  });
+}