feat(iios): retention_policy_snapshot + sweep (archive→redact, hold-aware) (P9)

Adds IiosRetentionPolicySnapshot (per-interaction frozen lifecycle timestamps)
+ IiosInteraction.dataClass, and a RetentionService whose sweep captures
snapshots then archives (status change) and, past delete_after, redacts content
in place (reusing the Slice-8 tombstone) — never a hard delete. An active
compliance hold blocks both; every action is audited and tenant-scopeable.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/prisma/schema.prisma

@@ -435,6 +435,7 @@ model IiosInteraction {
   occurredAt          DateTime            @default(now())
   receivedAt          DateTime            @default(now())
   status              IiosDeliveryState   @default(RECEIVED)
+  dataClass           String              @default("internal") // envelope data class; drives retention window (P9)
   policyDecisionRef   String?
   consentReceiptRef   String?
   crreBundleRef       String?
@@ -493,6 +494,27 @@ model IiosProcessedEvent {
   @@id([consumerName, eventId])
 }
 
+/// Per-resource retention snapshot (P9). Absolute lifecycle timestamps frozen from the
+/// resource's age + policy window; read by the retention sweep. delete = redact-in-place.
+model IiosRetentionPolicySnapshot {
+  id              String    @id @default(cuid())
+  policyKey       String
+  scopeSnapshotId String
+  targetType      String // 'interaction'
+  targetId        String
+  dataClass       String
+  retainUntil     DateTime?
+  archiveAfter    DateTime
+  deleteAfter     DateTime
+  sourceVersion   String    @default("v1")
+  status          String    @default("ACTIVE") // ACTIVE | ARCHIVED | REDACTED
+  createdAt       DateTime  @default(now())
+
+  @@unique([targetType, targetId])
+  @@index([status, deleteAfter])
+  @@index([scopeSnapshotId, status])
+}
+
 /// Legal/compliance hold (P9 DSR). An ACTIVE, unexpired hold over a target BLOCKS
 /// erasure/retention deletion until an authorised release. Never auto-released.
 model IiosComplianceHold {