diff --git a/backend/app/routers/knowledge.py b/backend/app/routers/knowledge.py
index 560eed4..f57cc86 100644
--- a/backend/app/routers/knowledge.py
+++ b/backend/app/routers/knowledge.py
@@ -124,11 +124,8 @@ def get_playbook_by_technique_type(
 ):
     pb = pb_svc.get_playbook_by_technique_type(db, technique_id, playbook_type)
     if not pb:
-        from app.domain.errors import DomainError
-        raise DomainError(
-            f"No '{playbook_type}' playbook for technique {technique_id}",
-            status_code=404,
-        )
+        from app.domain.errors import EntityNotFoundError
+        raise EntityNotFoundError("Playbook", f"{technique_id}/{playbook_type}")
     return pb
 
 
diff --git a/backend/app/services/lesson_learned_service.py b/backend/app/services/lesson_learned_service.py
index 236bef5..57aeba1 100644
--- a/backend/app/services/lesson_learned_service.py
+++ b/backend/app/services/lesson_learned_service.py
@@ -6,7 +6,7 @@ from uuid import UUID
 
 from sqlalchemy.orm import Session
 
-from app.domain.errors import DomainError
+from app.domain.errors import EntityNotFoundError
 from app.models.knowledge import LessonLearned
 
 
@@ -16,7 +16,7 @@ def _get_or_404(db: Session, ll_id: UUID) -> LessonLearned:
         LessonLearned.is_active == True,
     ).first()
     if not ll:
-        raise DomainError(f"Lesson Learned {ll_id} not found", status_code=404)
+        raise EntityNotFoundError("LessonLearned", str(ll_id))
     return ll
 
 
diff --git a/backend/app/services/playbook_service.py b/backend/app/services/playbook_service.py
index 3f72600..ed9b478 100644
--- a/backend/app/services/playbook_service.py
+++ b/backend/app/services/playbook_service.py
@@ -6,7 +6,9 @@ from uuid import UUID
 
 from sqlalchemy.orm import Session
 
-from app.domain.errors import DomainError
+from app.domain.errors import (
+    DomainError, EntityNotFoundError, DuplicateEntityError, BusinessRuleViolation
+)
 from app.models.knowledge import Playbook, PlaybookVersion
 from app.models.technique import Technique
 
@@ -17,7 +19,7 @@ def _get_or_404(db: Session, playbook_id: UUID) -> Playbook:
         Playbook.is_active == True,
     ).first()
     if not pb:
-        raise DomainError(f"Playbook {playbook_id} not found", status_code=404)
+        raise EntityNotFoundError("Playbook", str(playbook_id))
     return pb
 
 
@@ -88,7 +90,7 @@ def create_playbook(db: Session, data: dict, user_id: UUID) -> Playbook:
     # Validate technique exists
     tech = db.query(Technique).filter(Technique.id == technique_id).first()
     if not tech:
-        raise DomainError(f"Technique {technique_id} not found", status_code=404)
+        raise EntityNotFoundError("Technique", str(technique_id))
 
     # Check for existing (even soft-deleted) to reactivate
     existing = db.query(Playbook).filter(
@@ -98,10 +100,10 @@ def create_playbook(db: Session, data: dict, user_id: UUID) -> Playbook:
 
     if existing:
         if existing.is_active:
-            raise DomainError(
-                f"Playbook ({playbook_type}) for technique {technique_id} already exists. "
-                "Use PATCH to update it.",
-                status_code=409,
+            raise DuplicateEntityError(
+                "Playbook",
+                "technique_id+playbook_type",
+                f"{technique_id}/{playbook_type}",
             )
         # Reactivate soft-deleted playbook
         existing.is_active    = True
@@ -170,9 +172,7 @@ def restore_version(db: Session, playbook_id: UUID, version_number: int, user_id
         PlaybookVersion.version == version_number,
     ).first()
     if not snap:
-        raise DomainError(
-            f"Version {version_number} not found for playbook {playbook_id}", status_code=404
-        )
+        raise EntityNotFoundError("PlaybookVersion", f"{playbook_id}/v{version_number}")
 
     # Snapshot current state before restoring
     _snapshot(db, pb, user_id, f"Auto-snapshot before restore to v{version_number}")