Implement basic event deduplication

apps/api/src/database/migrations/2026-06-03.ts

@@ -17,6 +17,15 @@ export async function up(db: Kysely<any>): Promise<void> {
         .addColumn("rate_limits", "integer", (cb) => cb.notNull().defaultTo(0))
         .addColumn("has_failed", "boolean", (cb) => cb.notNull().defaultTo(false))
         .addColumn("last_error", "jsonb")
+        .addColumn("dedupe_key", "text")
+        .execute()
+
+    await db.schema.createIndex("events_idx_dedupe_key")
+        .on("events")
+        .columns(["group", "type", "dedupe_key"])
+        .unique()
+        .where("dedupe_key", "is not", null)
+        .where(sql.ref("ended_at"), "is", null)
         .execute()
 
     // TABLE: STANDARDS_DATASETS
@@ -60,6 +69,8 @@ export async function down(db: Kysely<any>): Promise<void> {
     // TABLE: EVENTS
     await db.schema.dropTable("events").ifExists().execute()
 
+    await db.schema.dropIndex("events_idx_dedupe_key").ifExists().execute();
+
     // TABLE: CALCULATORS
     await db.schema.dropTable("calculators").ifExists().execute()