feat(PBI-79/ST-1339): createSprintWithSelectionAction + banner wire-up

actions/sprints.ts:
- Nieuwe createSprintWithSelectionAction(productId, metadata, pbiIntent,
  storyOverrides).
- Server-side intent-resolve:
  1. Voor elke PBI met intent='all': fetch child-story-IDs minus
     storyOverrides[pbi].remove.
  2. Plus storyOverrides[*].add (cross-PBI cherrypick toegestaan).
- Eligibility-filter via partitionByEligibility (sprint_id IS NULL + status
  != DONE; stories in andere OPEN sprint → conflicts.crossSprint).
- Transactie wrapt sprint.create + story.updateMany (status='IN_SPRINT') +
  task.updateMany (sprint_id cascade) — alles atomair.
- setActiveSprintInSettings na success.
- Return: { success, sprintId, affectedStoryIds, affectedPbiIds,
  affectedTaskIds, conflicts: { notEligible, crossSprint } } of error.

components/backlog/sprint-definition-banner.tsx:
- 'Sprint aanmaken'-knop sluit aan op createSprintWithSelectionAction;
  toast bij conflicts, success-toast anders, router.refresh() voor SSR
  cycle. Pending draft wordt door de action zelf nog niet expliciet gewist
  — dat gebeurt via revalidatePath en kan in ST-1340 finetuned worden.

Tests: __tests__/actions/create-sprint-with-selection.test.ts (6 cases)
dekken intent-resolve, override-respect, cross-sprint conflict, transactie-
binding van story.status + task.sprint_id, return-shape, en error-pad.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

actions/sprints.ts

@@ -15,8 +15,158 @@ import { enforceUserRateLimit } from '@/lib/rate-limit'
 import { propagateStatusUpwards } from '@/lib/tasks-status-update'
 import { createWithCodeRetry, generateNextSprintCode } from '@/lib/code-server'
 import { setActiveSprintInSettings } from '@/lib/active-sprint'
+import { partitionByEligibility } from '@/lib/sprint-conflicts'
 import { z } from 'zod'
 
+const StoryOverrideSchema = z.object({
+  add: z.array(z.string()),
+  remove: z.array(z.string()),
+})
+
+const createSprintWithSelectionSchema = z.object({
+  productId: z.string().min(1),
+  metadata: z.object({
+    goal: z.string().min(1).max(2000),
+    startAt: z.string().date().optional(),
+    endAt: z.string().date().optional(),
+  }),
+  pbiIntent: z.record(z.string(), z.enum(['all', 'none'])).default({}),
+  storyOverrides: z.record(z.string(), StoryOverrideSchema).default({}),
+})
+
+export type CreateSprintWithSelectionInput = z.infer<
+  typeof createSprintWithSelectionSchema
+>
+
+type SprintCreateConflicts = {
+  notEligible: { storyId: string; reason: 'DONE' | 'IN_OTHER_SPRINT' }[]
+  crossSprint: { storyId: string; sprintId: string; sprintName: string }[]
+}
+
+export type CreateSprintWithSelectionResult =
+  | {
+      success: true
+      sprintId: string
+      affectedStoryIds: string[]
+      affectedPbiIds: string[]
+      affectedTaskIds: string[]
+      conflicts: SprintCreateConflicts
+    }
+  | { error: string; code: number }
+
+export async function createSprintWithSelectionAction(
+  input: CreateSprintWithSelectionInput,
+): Promise<CreateSprintWithSelectionResult> {
+  const session = await getSession()
+  if (!session.userId) return { error: 'Niet ingelogd', code: 403 }
+  if (session.isDemo) return { error: 'Niet beschikbaar in demo-modus', code: 403 }
+
+  const limited = enforceUserRateLimit('create-sprint', session.userId)
+  if (limited) return { error: limited.error, code: limited.code }
+
+  const parsed = createSprintWithSelectionSchema.safeParse(input)
+  if (!parsed.success) return { error: 'Validatie mislukt', code: 422 }
+
+  const product = await getAccessibleProduct(parsed.data.productId, session.userId)
+  if (!product) return { error: 'Product niet gevonden', code: 403 }
+
+  // Resolveer intent + per-PBI overrides naar concrete story-IDs.
+  const allPbiAllIds = Object.entries(parsed.data.pbiIntent)
+    .filter(([, intent]) => intent === 'all')
+    .map(([pbiId]) => pbiId)
+
+  // Stap 1: alle child-stories voor PBI's met intent='all'.
+  let candidate: string[] = []
+  if (allPbiAllIds.length > 0) {
+    const rows = await prisma.story.findMany({
+      where: { pbi_id: { in: allPbiAllIds }, product_id: parsed.data.productId },
+      select: { id: true, pbi_id: true },
+    })
+    const removedSet = new Set<string>()
+    for (const [pbiId, override] of Object.entries(parsed.data.storyOverrides)) {
+      for (const id of override.remove) removedSet.add(`${pbiId}:${id}`)
+    }
+    candidate = rows
+      .filter((row) => !removedSet.has(`${row.pbi_id}:${row.id}`))
+      .map((row) => row.id)
+  }
+
+  // Stap 2: storyOverrides.add — werkt voor zowel intent='none' als 'all' (extra
+  // toevoegingen). Dedupliceren met candidates uit stap 1.
+  const candidateSet = new Set(candidate)
+  for (const override of Object.values(parsed.data.storyOverrides)) {
+    for (const id of override.add) candidateSet.add(id)
+  }
+  const candidateIds = Array.from(candidateSet)
+
+  // Eligibility-filter (incl. cross-sprint guard).
+  const partition = await partitionByEligibility(prisma, candidateIds)
+
+  if (partition.eligible.length === 0) {
+    return {
+      error: 'Geen eligible stories voor deze sprint',
+      code: 422,
+    }
+  }
+
+  const sprint = await createWithCodeRetry(
+    () => generateNextSprintCode(parsed.data.productId),
+    (code) =>
+      prisma.$transaction(async (tx) => {
+        const created = await tx.sprint.create({
+          data: {
+            product_id: parsed.data.productId,
+            code,
+            sprint_goal: parsed.data.metadata.goal,
+            status: 'OPEN',
+            start_date: parseDate(parsed.data.metadata.startAt),
+            end_date: parseDate(parsed.data.metadata.endAt),
+          },
+        })
+        await tx.story.updateMany({
+          where: { id: { in: partition.eligible } },
+          data: { sprint_id: created.id, status: 'IN_SPRINT' },
+        })
+        await tx.task.updateMany({
+          where: { story_id: { in: partition.eligible } },
+          data: { sprint_id: created.id },
+        })
+        return created
+      }),
+  )
+
+  // Snapshot affected pbi/task IDs voor client-store patches.
+  const affectedStories = await prisma.story.findMany({
+    where: { id: { in: partition.eligible } },
+    select: { pbi_id: true },
+  })
+  const affectedPbiIds = Array.from(new Set(affectedStories.map((s) => s.pbi_id)))
+  const affectedTasks = await prisma.task.findMany({
+    where: { story_id: { in: partition.eligible } },
+    select: { id: true },
+  })
+  const affectedTaskIds = affectedTasks.map((t) => t.id)
+
+  await setActiveSprintInSettings(
+    session.userId,
+    parsed.data.productId,
+    sprint.id,
+  )
+  revalidatePath(`/products/${parsed.data.productId}`, 'layout')
+
+  return {
+    success: true,
+    sprintId: sprint.id,
+    affectedStoryIds: partition.eligible,
+    affectedPbiIds,
+    affectedTaskIds,
+    conflicts: {
+      notEligible: partition.notEligible,
+      crossSprint: partition.crossSprint,
+    },
+  }
+}
+
 async function getSession() {
   return getIronSession<SessionData>(await cookies(), sessionOptions)
 }