diff --git a/src/commander_ai_lab/deck_builder/core/__init__.py b/src/commander_ai_lab/deck_builder/core/__init__.py
index fd00f54..fd67eb5 100644
--- a/src/commander_ai_lab/deck_builder/core/__init__.py
+++ b/src/commander_ai_lab/deck_builder/core/__init__.py
@@ -1 +1,27 @@
-# core subpackage
+"""Core subpackage – models, rules, and collection utilities."""
+
+from .models import (
+    BuildRequest,
+    BuildResult,
+    CardEntry,
+    CommanderDeck,
+    DeckRatios,
+)
+from .rules_engine import (
+    check_ban_list,
+    filter_by_color_identity,
+    validate_deck,
+)
+from .collection_filter import filter_names_by_collection
+
+__all__ = [
+    "BuildRequest",
+    "BuildResult",
+    "CardEntry",
+    "CommanderDeck",
+    "DeckRatios",
+    "check_ban_list",
+    "filter_by_color_identity",
+    "validate_deck",
+    "filter_names_by_collection",
+]