feat(service): P3.1 inbox tables + extract ActorResolver

IiosInboxItem + IiosInboxItemStateHistory (migration inbox-init). Extracted
resolveScope/resolveActor/ensureParticipant into a shared ActorResolver
(IdentityModule) so message + inbox layers share identity resolution; MessageService
delegates (P2 tests unchanged).

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

packages/iios-service/prisma/schema.prisma

@@ -75,6 +75,26 @@ enum IiosReceiptKind {
   RATE_LIMITED
 }
 
+enum IiosInboxItemKind {
+  NEEDS_REPLY
+  NEEDS_REVIEW
+  NEEDS_APPROVAL
+  SUPPORT_UPDATE
+  MEETING_FOLLOWUP
+  DIGEST
+  SYSTEM_ALERT
+  CRM_OWNER_INTEREST
+}
+
+enum IiosInboxState {
+  OPEN
+  SNOOZED
+  DONE
+  ARCHIVED
+  CANCELLED
+  STALE
+}
+
 // ─── Kernel tables ────────────────────────────────────────────────
 
 /// Frozen six-vector scope. orgId + appId are REQUIRED (no global-by-null).
@@ -93,6 +113,7 @@ model IiosScope {
   channels      IiosChannel[]
   threads       IiosThread[]
   interactions  IiosInteraction[]
+  inboxItems    IiosInboxItem[]
 
   @@index([orgId, appId, tenantId])
 }
@@ -135,6 +156,7 @@ model IiosActorRef {
   interactions       IiosInteraction[]
   receipts           IiosMessageReceipt[]
   unreadCounters     IiosUnreadCounter[]
+  inboxItemsOwned    IiosInboxItem[]
 }
 
 /// A configured channel surface (PORTAL in P1).
@@ -177,6 +199,7 @@ model IiosThread {
   participants   IiosThreadParticipant[]
   interactions   IiosInteraction[]
   unreadCounters IiosUnreadCounter[]
+  inboxItems     IiosInboxItem[]
 
   @@index([scopeId, status])
 }
@@ -219,8 +242,9 @@ model IiosInteraction {
   traceId             String?
   metadata            Json?
 
-  parts    IiosMessagePart[]
-  receipts IiosMessageReceipt[]
+  parts      IiosMessagePart[]
+  receipts   IiosMessageReceipt[]
+  inboxItems IiosInboxItem[]
 
   @@unique([scopeId, idempotencyKey])
   @@index([threadId, occurredAt])
@@ -299,3 +323,49 @@ model IiosUnreadCounter {
 
   @@id([threadId, actorId])
 }
+
+// ─── P3: Inbox (work/awareness surface) ───────────────────────────
+
+/// A durable action/awareness item owned by one actor. Fed by the event
+/// projector (deterministic, collapse-per-thread). NOT a thin unread projection.
+model IiosInboxItem {
+  id                  String            @id @default(cuid())
+  scopeId             String
+  scope               IiosScope         @relation(fields: [scopeId], references: [id], onDelete: Cascade)
+  ownerActorId        String
+  ownerActor          IiosActorRef      @relation(fields: [ownerActorId], references: [id])
+  kind                IiosInboxItemKind
+  state               IiosInboxState    @default(OPEN)
+  title               String
+  summary             String?
+  priority            String            @default("NORMAL")
+  dueAt               DateTime?
+  sourceInteractionId String?
+  sourceInteraction   IiosInteraction?  @relation(fields: [sourceInteractionId], references: [id])
+  threadId            String?
+  thread              IiosThread?       @relation(fields: [threadId], references: [id])
+  traceId             String?
+  actionRef           Json?
+  policyDecisionRef   String?
+  createdAt           DateTime          @default(now())
+  updatedAt           DateTime          @updatedAt
+  metadata            Json?
+
+  stateHistory IiosInboxItemStateHistory[]
+
+  @@index([ownerActorId, state, priority])
+}
+
+/// Audit trail of inbox-item state transitions.
+model IiosInboxItemStateHistory {
+  id          String          @id @default(cuid())
+  inboxItemId String
+  inboxItem   IiosInboxItem   @relation(fields: [inboxItemId], references: [id], onDelete: Cascade)
+  fromState   IiosInboxState?
+  toState     IiosInboxState
+  actorId     String?
+  reasonCode  String?
+  at          DateTime        @default(now())
+
+  @@index([inboxItemId])
+}