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);
       });

tests/drizzle-timelines.test.ts

@@ -0,0 +1,95 @@
+import type { ModuleDatabase } from "@ekklesia/module-sdk";
+import { describe, expect, it } from "vitest";
+import { createTimelineStore } from "../src/server/store/drizzle-timelines.js";
+import type { NewStoredSlot } from "../src/server/store/types.js";
+
+const TIMELINE_ID = "00000000-0000-4000-8000-000000000001";
+
+function slot(id: string): NewStoredSlot {
+  return {
+    durationOverrideMs: null,
+    eligibleFrom: null,
+    eligibleUntil: null,
+    enabled: true,
+    id,
+    itemId: "image-1",
+    kind: "pinned-item",
+    presentation: {
+      backgroundColor: null,
+      backgroundDarkened: null,
+      backgroundMode: null,
+      blurPixels: null,
+      foregroundShadow: null,
+    },
+    providerId: "signage.native-images",
+    sourceId: null,
+    timelineId: TIMELINE_ID,
+  };
+}
+
+/**
+ * A narrow database contract double for the production timeline store.
+ *
+ * Unlike the service-level memory store, it enforces the shipped PostgreSQL
+ * `signage_timeline_slots_position_check` on every insert and update. That is the boundary the
+ * deployed bug crossed: the old collision-avoidance algorithm used negative positions, so the
+ * actual database rejected a native-image slot before playback ever had content to resolve.
+ */
+function constraintDatabase(existing: readonly { id: string; position: number }[]): {
+  readonly database: ModuleDatabase;
+  readonly positions: number[];
+} {
+  const positions: number[] = [];
+  const enforce = (values: { position?: unknown }): void => {
+    if (typeof values.position === "number") {
+      expect(values.position).toBeGreaterThanOrEqual(0);
+      positions.push(values.position);
+    }
+  };
+  const transaction = {
+    insert: () => ({
+      values: async (values: { position?: unknown }) => enforce(values),
+    }),
+    select: () => ({
+      from: () => ({
+        where: () => ({
+          orderBy: async () => existing,
+        }),
+      }),
+    }),
+    update: () => ({
+      set: (values: { position?: unknown }) => ({
+        where: async () => enforce(values),
+      }),
+    }),
+  };
+  return {
+    database: {
+      transaction: async (operation: (value: typeof transaction) => Promise<unknown>) => operation(transaction),
+    } as unknown as ModuleDatabase,
+    positions,
+  };
+}
+
+describe("production timeline slot ordering", () => {
+  it("creates the first pinned native image without violating the database position constraint", async () => {
+    const { database, positions } = constraintDatabase([]);
+
+    await createTimelineStore(database).addSlot(slot("00000000-0000-4000-8000-000000000002"));
+
+    expect(positions).toEqual([1, 2, 0]);
+  });
+
+  it("reorders through a non-negative temporary range before writing the final order", async () => {
+    const first = "00000000-0000-4000-8000-000000000002";
+    const second = "00000000-0000-4000-8000-000000000003";
+    const { database, positions } = constraintDatabase([
+      { id: first, position: 0 },
+      { id: second, position: 1 },
+    ]);
+
+    await createTimelineStore(database).reorderSlots(TIMELINE_ID, [second, first]);
+
+    expect(positions).toEqual([3, 4, 0, 1]);
+  });
+});