chore(database): drop unused TaskRun status composite index

Author: ericallam

.server-changes/drop-taskrun-status-composite-idx.md

@@ -0,0 +1,6 @@
+---
+area: webapp
+type: improvement
+---
+
+Reduce primary database write load on `TaskRun` by dropping an unused composite index on `(status, runtimeEnvironmentId, createdAt, id)`. After gating the legacy `WAITING_FOR_DEPLOY` drain to V1-engine workers only, no V2 Prisma query uses this index while it was still being maintained on every `TaskRun` INSERT/UPDATE.

internal-packages/database/prisma/migrations/20260525083555_drop_task_run_status_runtime_environment_id_created_at_id_idx/migration.sql

@@ -0,0 +1,2 @@
+-- DropIndex
+DROP INDEX CONCURRENTLY IF EXISTS "public"."TaskRun_status_runtimeEnvironmentId_createdAt_id_idx";

internal-packages/database/prisma/schema.prisma

@@ -1089,7 +1089,6 @@ model TaskRun {
   @@index([runtimeEnvironmentId, batchId])
   @@index([runtimeEnvironmentId, createdAt(sort: Desc)])
   @@index([createdAt], type: Brin)
-  @@index([status, runtimeEnvironmentId, createdAt, id(sort: Desc)])
 }
 
 model TaskRunTemplate {