feat(ST-cmovhvegf): add existingPbi pre-check in materializeIdeaPlanAction

- Adds options.allowAlongside parameter to control behaviour when a PBI
  with executed tasks already exists.
- Returns 409 PBI_HAS_ACTIVE_TASKS:<code> when tasks are DONE/IN_PROGRESS
  and allowAlongside is not set.
- Auto-deletes the old PBI inside the transaction when no tasks have been
  executed (atomic replace).
- Alongside mode (allowAlongside=true) skips deletion and creates a new PBI.

actions/ideas.ts

@@ -540,6 +540,7 @@ function nextNumber(existing: (string | null)[], re: RegExp): number {
 
 export async function materializeIdeaPlanAction(
   id: string,
+  options?: { allowAlongside?: boolean },
 ): Promise<ActionResult<{ pbi_id: string; pbi_code: string; story_ids: string[]; task_ids: string[] }>> {
   const session = await getSession()
   if (!session.userId) return { error: 'Niet ingelogd', code: 401 }
@@ -550,7 +551,7 @@ export async function materializeIdeaPlanAction(
 
   const idea = await prisma.idea.findFirst({
     where: { id, user_id: session.userId },
-    select: { id: true, status: true, product_id: true, plan_md: true },
+    select: { id: true, status: true, product_id: true, plan_md: true, pbi_id: true },
   })
   if (!idea) return { error: 'Idee niet gevonden', code: 404 }
   if (idea.status !== 'PLAN_READY') {
@@ -574,8 +575,36 @@ export async function materializeIdeaPlanAction(
   const productId = idea.product_id
   const plan = parsed.plan
 
+  let oldPbiId: string | null = null
+  if (idea.pbi_id) {
+    const executedCount = await prisma.task.count({
+      where: {
+        story: { pbi_id: idea.pbi_id },
+        status: { in: ['DONE', 'IN_PROGRESS'] },
+      },
+    })
+    if (executedCount > 0 && !options?.allowAlongside) {
+      const existingPbi = await prisma.pbi.findUnique({
+        where: { id: idea.pbi_id },
+        select: { code: true },
+      })
+      return {
+        error: `PBI_HAS_ACTIVE_TASKS:${existingPbi?.code ?? idea.pbi_id}`,
+        code: 409,
+      }
+    }
+    if (executedCount === 0) {
+      oldPbiId = idea.pbi_id
+    }
+    // executedCount > 0 && allowAlongside: doorgaan zonder delete
+  }
+
   try {
     const result = await prisma.$transaction(async (tx) => {
+      if (oldPbiId) {
+        await tx.pbi.delete({ where: { id: oldPbiId } })
+      }
+
       // Codes: één keer SELECT max per type binnen de transactie. Bij P2002
       // (race met andere materialize) abort de transactie en gooien we 409.
       const [existingPbis, existingStories, existingTasks] = await Promise.all([