fix: preserve valid timeline slot positions

src/server/store/drizzle-timelines.ts

@@ -112,20 +112,21 @@ export function createTimelineStore(database: ModuleDatabase): SignageTimelineSt
   /**
    * Rewrites `position` for one timeline from an explicit order.
    *
-   * Positions are written in two passes, through a temporary negative range, because the unique
+   * Positions are written in two passes, through a temporary high range, because the unique
    * `(timeline_id, position)` index is checked per statement: moving a slot from 3 to 1 while
-   * another still holds 1 would collide. Negative positions are outside every real value, so the
-   * intermediate state cannot be mistaken for an order.
+   * another still holds 1 would collide. Temporary positions sit beyond the final order while
+   * remaining inside the database's non-negative constraint.
    */
   async function renumber(
     transaction: ModuleDatabase,
     timelineId: string,
     orderedSlotIds: readonly string[],
   ): Promise<void> {
+    const temporaryOffset = orderedSlotIds.length + 1;
     for (const [index, slotId] of orderedSlotIds.entries()) {
       await transaction
         .update(timelineSlots)
-        .set({ position: -1 - index })
+        .set({ position: temporaryOffset + index })
         .where(eq(timelineSlots.id, slotId));
     }
     for (const [index, slotId] of orderedSlotIds.entries()) {
@@ -175,7 +176,7 @@ export function createTimelineStore(database: ModuleDatabase): SignageTimelineSt
           position === undefined
             ? existing.length
             : Math.max(0, Math.min(position, existing.length));
-        await transaction.insert(timelineSlots).values(slotValues(slot, -1_000_000));
+        await transaction.insert(timelineSlots).values(slotValues(slot, existing.length + 1));
         const next = [...existing.slice(0, index), slot.id, ...existing.slice(index)];
         await renumber(transaction, slot.timelineId, next);
       });