diff --git a/server/src/nest/assignments/assignments.controller.ts b/server/src/nest/assignments/assignments.controller.ts
index e942dd845..d2c0dbecd 100644
--- a/server/src/nest/assignments/assignments.controller.ts
+++ b/server/src/nest/assignments/assignments.controller.ts
@@ -175,7 +175,9 @@ export class AssignmentOpsController {
     if (!this.assignments.getAssignmentForTrip(id, tripId)) {
       throw new HttpException({ error: 'Assignment not found' }, 404);
     }
-    const assignment = this.assignments.setLegTransportMode(id, body.transport_mode ?? null);
+    const assignment = body.direction === 'incoming'
+      ? this.assignments.setIncomingLegTransportMode(id, body.transport_mode ?? null)
+      : this.assignments.setLegTransportMode(id, body.transport_mode ?? null);
     this.assignments.broadcast(tripId, 'assignment:updated', { assignment }, socketId);
     return { assignment };
   }
diff --git a/server/src/nest/assignments/assignments.service.ts b/server/src/nest/assignments/assignments.service.ts
index 8e901a666..379943811 100644
--- a/server/src/nest/assignments/assignments.service.ts
+++ b/server/src/nest/assignments/assignments.service.ts
@@ -272,6 +272,17 @@ export class AssignmentsService {
     return this.getAssignmentWithPlace(Number(id));
   }
 
+  /**
+   * Set the travel mode of the leg arriving at this stop (#1281 boundary legs).
+   * Mirrors setLegTransportMode but targets incoming_leg_transport_mode; inert
+   * when the previous timeline element is a place (the column is only read for
+   * non-place origins like a booking arrival or a morning hotel departure).
+   */
+  setIncomingLegTransportMode(id: string | number, mode: string | null) {
+    this.dbs.run('UPDATE day_assignments SET incoming_leg_transport_mode = ? WHERE id = ?', mode ?? null, id);
+    return this.getAssignmentWithPlace(Number(id));
+  }
+
   setParticipants(assignmentId: string | number, userIds: number[]) {
     this.dbs.transaction(() => {
       this.dbs.run('DELETE FROM assignment_participants WHERE assignment_id = ?', assignmentId);
diff --git a/server/tests/integration/leg-mode-incoming.test.ts b/server/tests/integration/leg-mode-incoming.test.ts
index 2f3a34e4b..3b55884d2 100644
--- a/server/tests/integration/leg-mode-incoming.test.ts
+++ b/server/tests/integration/leg-mode-incoming.test.ts
@@ -124,4 +124,74 @@ describe('incoming_leg_transport_mode read-path parity', () => {
     const a = foundDay.assignments.find((x: any) => x.id === assignmentId);
     expect(a.incoming_leg_transport_mode).toBe('transit');
   });
+
+  // ───────────────────────────────────────────────────────────────────────────
+  // Write path — PUT .../transport gains `direction` (outgoing|incoming).
+  // ───────────────────────────────────────────────────────────────────────────
+
+  describe('PUT /assignments/:id/transport direction', () => {
+    it('defaults to outgoing (back-compat)', async () => {
+      const { user } = createUser(testDb2);
+      const trip = createTrip(testDb2, user.id);
+      const day = createDay(testDb2, trip.id, { date: '2025-06-01' });
+      const place = createPlace(testDb2, trip.id, { name: 'Test Place' });
+
+      const create = await request(app)
+        .post(`/api/trips/${trip.id}/days/${day.id}/assignments`)
+        .set('Cookie', authCookie(user.id))
+        .send({ place_id: place.id });
+      const assignmentId = create.body.assignment.id;
+
+      const res = await request(app)
+        .put(`/api/trips/${trip.id}/assignments/${assignmentId}/transport`)
+        .set('Cookie', authCookie(user.id))
+        .send({ transport_mode: 'cycling' });
+      expect(res.status).toBe(200);
+
+      const row = testDb2.prepare('SELECT leg_transport_mode, incoming_leg_transport_mode FROM day_assignments WHERE id = ?').get(assignmentId);
+      expect(row.leg_transport_mode).toBe('cycling');
+      expect(row.incoming_leg_transport_mode).toBeNull();
+    });
+
+    it("direction: 'incoming' writes the incoming column", async () => {
+      const { user } = createUser(testDb2);
+      const trip = createTrip(testDb2, user.id);
+      const day = createDay(testDb2, trip.id, { date: '2025-06-01' });
+      const place = createPlace(testDb2, trip.id, { name: 'Test Place' });
+
+      const create = await request(app)
+        .post(`/api/trips/${trip.id}/days/${day.id}/assignments`)
+        .set('Cookie', authCookie(user.id))
+        .send({ place_id: place.id });
+      const assignmentId = create.body.assignment.id;
+
+      const res = await request(app)
+        .put(`/api/trips/${trip.id}/assignments/${assignmentId}/transport`)
+        .set('Cookie', authCookie(user.id))
+        .send({ transport_mode: 'transit', direction: 'incoming' });
+      expect(res.status).toBe(200);
+
+      const row = testDb2.prepare('SELECT incoming_leg_transport_mode FROM day_assignments WHERE id = ?').get(assignmentId);
+      expect(row.incoming_leg_transport_mode).toBe('transit');
+    });
+
+    it('rejects an invalid direction with 400', async () => {
+      const { user } = createUser(testDb2);
+      const trip = createTrip(testDb2, user.id);
+      const day = createDay(testDb2, trip.id, { date: '2025-06-01' });
+      const place = createPlace(testDb2, trip.id, { name: 'Test Place' });
+
+      const create = await request(app)
+        .post(`/api/trips/${trip.id}/days/${day.id}/assignments`)
+        .set('Cookie', authCookie(user.id))
+        .send({ place_id: place.id });
+      const assignmentId = create.body.assignment.id;
+
+      const res = await request(app)
+        .put(`/api/trips/${trip.id}/assignments/${assignmentId}/transport`)
+        .set('Cookie', authCookie(user.id))
+        .send({ transport_mode: 'walking', direction: 'sideways' });
+      expect(res.status).toBe(400);
+    });
+  });
 });
diff --git a/shared/src/assignment/assignment.schema.ts b/shared/src/assignment/assignment.schema.ts
index 0a70fe069..f81d827c3 100644
--- a/shared/src/assignment/assignment.schema.ts
+++ b/shared/src/assignment/assignment.schema.ts
@@ -83,6 +83,9 @@ export const assignmentTransportRequestSchema = z.object({
   // The legacy route read `body.transport_mode ?? null`, so an absent key
   // behaves like an explicit null — keep it optional on the wire.
   transport_mode: z.string().nullable().optional(),
+  // Which leg this write targets: the one leaving this stop (default, and the
+  // legacy behaviour) or the one arriving at it (#1281 boundary legs).
+  direction: z.enum(['outgoing', 'incoming']).default('outgoing'),
 });
 export type AssignmentTransportRequest = z.infer<typeof assignmentTransportRequestSchema>;