fix: use integer instead of serial for taskNumber, add backfill on startup

serial caused db:push failure on existing tables. Now uses nullable
integer with app-level sequencing and startup backfill.

backend/src/index.ts

@@ -2,9 +2,38 @@ import { Elysia } from "elysia";
 import { cors } from "@elysiajs/cors";
 import { taskRoutes } from "./routes/tasks";
 import { auth } from "./lib/auth";
+import { db } from "./db";
+import { tasks } from "./db/schema";
+import { isNull, asc, sql } from "drizzle-orm";
 
 const PORT = process.env.PORT || 3100;
 
+// Backfill task numbers for existing tasks that don't have one
+async function backfillTaskNumbers() {
+  const unnumbered = await db
+    .select()
+    .from(tasks)
+    .where(isNull(tasks.taskNumber))
+    .orderBy(asc(tasks.createdAt));
+
+  if (unnumbered.length === 0) return;
+
+  const maxNum = await db
+    .select({ max: sql<number>`COALESCE(MAX(${tasks.taskNumber}), 0)` })
+    .from(tasks);
+  let next = (maxNum[0]?.max ?? 0) + 1;
+
+  for (const task of unnumbered) {
+    await db
+      .update(tasks)
+      .set({ taskNumber: next++ })
+      .where(sql`${tasks.id} = ${task.id}`);
+  }
+  console.log(`Backfilled ${unnumbered.length} task numbers (${next - unnumbered.length} to ${next - 1})`);
+}
+
+backfillTaskNumbers().catch(console.error);
+
 const app = new Elysia()
   .use(
     cors({