feat(schema): make note_id and is_reversed NOT NULL

All cards now require note association - legacy card support removed.
This aligns with the note-based card architecture introduced in Phase 8.

- Add database migration for NOT NULL constraints
- Update client Dexie schema to version 3
- Remove LegacyCardItem component and legacy card handling
- Update sync schemas and type definitions
- Update all tests to use note-based cards

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

28 files changed, 1082 insertions, 353 deletions

diff --git a/drizzle/0003_brave_blacklash.sql b/drizzle/0003_brave_blacklash.sql
new file mode 100644
index 0000000..d129f36
--- /dev/null
+++ b/drizzle/0003_brave_blacklash.sql
@@ -0,0 +1,2 @@
+ALTER TABLE "cards" ALTER COLUMN "note_id" SET NOT NULL;--> statement-breakpoint
+ALTER TABLE "cards" ALTER COLUMN "is_reversed" SET NOT NULL;
\ No newline at end of file
diff --git a/drizzle/meta/0003_snapshot.json b/drizzle/meta/0003_snapshot.json
new file mode 100644
index 0000000..1a46c49
--- /dev/null
+++ b/drizzle/meta/0003_snapshot.json
@@ -0,0 +1,837 @@
+{
+  "id": "64c4ab9c-4036-44de-99cb-c4b14f494a4d",
+  "prevId": "4b30f43f-1827-40c6-9814-d749334da729",
+  "version": "7",
+  "dialect": "postgresql",
+  "tables": {
+    "public.cards": {
+      "name": "cards",
+      "schema": "",
+      "columns": {
+        "id": {
+          "name": "id",
+          "type": "uuid",
+          "primaryKey": true,
+          "notNull": true,
+          "default": "gen_random_uuid()"
+        },
+        "deck_id": {
+          "name": "deck_id",
+          "type": "uuid",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "note_id": {
+          "name": "note_id",
+          "type": "uuid",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "is_reversed": {
+          "name": "is_reversed",
+          "type": "boolean",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "front": {
+          "name": "front",
+          "type": "text",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "back": {
+          "name": "back",
+          "type": "text",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "state": {
+          "name": "state",
+          "type": "smallint",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        },
+        "due": {
+          "name": "due",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "stability": {
+          "name": "stability",
+          "type": "real",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        },
+        "difficulty": {
+          "name": "difficulty",
+          "type": "real",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        },
+        "elapsed_days": {
+          "name": "elapsed_days",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        },
+        "scheduled_days": {
+          "name": "scheduled_days",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        },
+        "reps": {
+          "name": "reps",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        },
+        "lapses": {
+          "name": "lapses",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        },
+        "last_review": {
+          "name": "last_review",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": false
+        },
+        "created_at": {
+          "name": "created_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "updated_at": {
+          "name": "updated_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "deleted_at": {
+          "name": "deleted_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": false
+        },
+        "sync_version": {
+          "name": "sync_version",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        }
+      },
+      "indexes": {},
+      "foreignKeys": {
+        "cards_deck_id_decks_id_fk": {
+          "name": "cards_deck_id_decks_id_fk",
+          "tableFrom": "cards",
+          "tableTo": "decks",
+          "columnsFrom": [
+            "deck_id"
+          ],
+          "columnsTo": [
+            "id"
+          ],
+          "onDelete": "no action",
+          "onUpdate": "no action"
+        },
+        "cards_note_id_notes_id_fk": {
+          "name": "cards_note_id_notes_id_fk",
+          "tableFrom": "cards",
+          "tableTo": "notes",
+          "columnsFrom": [
+            "note_id"
+          ],
+          "columnsTo": [
+            "id"
+          ],
+          "onDelete": "no action",
+          "onUpdate": "no action"
+        }
+      },
+      "compositePrimaryKeys": {},
+      "uniqueConstraints": {},
+      "policies": {},
+      "checkConstraints": {},
+      "isRLSEnabled": false
+    },
+    "public.decks": {
+      "name": "decks",
+      "schema": "",
+      "columns": {
+        "id": {
+          "name": "id",
+          "type": "uuid",
+          "primaryKey": true,
+          "notNull": true,
+          "default": "gen_random_uuid()"
+        },
+        "user_id": {
+          "name": "user_id",
+          "type": "uuid",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "name": {
+          "name": "name",
+          "type": "varchar(255)",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "description": {
+          "name": "description",
+          "type": "text",
+          "primaryKey": false,
+          "notNull": false
+        },
+        "new_cards_per_day": {
+          "name": "new_cards_per_day",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 20
+        },
+        "created_at": {
+          "name": "created_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "updated_at": {
+          "name": "updated_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "deleted_at": {
+          "name": "deleted_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": false
+        },
+        "sync_version": {
+          "name": "sync_version",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        }
+      },
+      "indexes": {},
+      "foreignKeys": {
+        "decks_user_id_users_id_fk": {
+          "name": "decks_user_id_users_id_fk",
+          "tableFrom": "decks",
+          "tableTo": "users",
+          "columnsFrom": [
+            "user_id"
+          ],
+          "columnsTo": [
+            "id"
+          ],
+          "onDelete": "no action",
+          "onUpdate": "no action"
+        }
+      },
+      "compositePrimaryKeys": {},
+      "uniqueConstraints": {},
+      "policies": {},
+      "checkConstraints": {},
+      "isRLSEnabled": false
+    },
+    "public.note_field_types": {
+      "name": "note_field_types",
+      "schema": "",
+      "columns": {
+        "id": {
+          "name": "id",
+          "type": "uuid",
+          "primaryKey": true,
+          "notNull": true,
+          "default": "gen_random_uuid()"
+        },
+        "note_type_id": {
+          "name": "note_type_id",
+          "type": "uuid",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "name": {
+          "name": "name",
+          "type": "varchar(255)",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "order": {
+          "name": "order",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "field_type": {
+          "name": "field_type",
+          "type": "varchar(50)",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "'text'"
+        },
+        "created_at": {
+          "name": "created_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "updated_at": {
+          "name": "updated_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "deleted_at": {
+          "name": "deleted_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": false
+        },
+        "sync_version": {
+          "name": "sync_version",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        }
+      },
+      "indexes": {},
+      "foreignKeys": {
+        "note_field_types_note_type_id_note_types_id_fk": {
+          "name": "note_field_types_note_type_id_note_types_id_fk",
+          "tableFrom": "note_field_types",
+          "tableTo": "note_types",
+          "columnsFrom": [
+            "note_type_id"
+          ],
+          "columnsTo": [
+            "id"
+          ],
+          "onDelete": "no action",
+          "onUpdate": "no action"
+        }
+      },
+      "compositePrimaryKeys": {},
+      "uniqueConstraints": {},
+      "policies": {},
+      "checkConstraints": {},
+      "isRLSEnabled": false
+    },
+    "public.note_field_values": {
+      "name": "note_field_values",
+      "schema": "",
+      "columns": {
+        "id": {
+          "name": "id",
+          "type": "uuid",
+          "primaryKey": true,
+          "notNull": true,
+          "default": "gen_random_uuid()"
+        },
+        "note_id": {
+          "name": "note_id",
+          "type": "uuid",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "note_field_type_id": {
+          "name": "note_field_type_id",
+          "type": "uuid",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "value": {
+          "name": "value",
+          "type": "text",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "created_at": {
+          "name": "created_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "updated_at": {
+          "name": "updated_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "sync_version": {
+          "name": "sync_version",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        }
+      },
+      "indexes": {},
+      "foreignKeys": {
+        "note_field_values_note_id_notes_id_fk": {
+          "name": "note_field_values_note_id_notes_id_fk",
+          "tableFrom": "note_field_values",
+          "tableTo": "notes",
+          "columnsFrom": [
+            "note_id"
+          ],
+          "columnsTo": [
+            "id"
+          ],
+          "onDelete": "no action",
+          "onUpdate": "no action"
+        },
+        "note_field_values_note_field_type_id_note_field_types_id_fk": {
+          "name": "note_field_values_note_field_type_id_note_field_types_id_fk",
+          "tableFrom": "note_field_values",
+          "tableTo": "note_field_types",
+          "columnsFrom": [
+            "note_field_type_id"
+          ],
+          "columnsTo": [
+            "id"
+          ],
+          "onDelete": "no action",
+          "onUpdate": "no action"
+        }
+      },
+      "compositePrimaryKeys": {},
+      "uniqueConstraints": {},
+      "policies": {},
+      "checkConstraints": {},
+      "isRLSEnabled": false
+    },
+    "public.note_types": {
+      "name": "note_types",
+      "schema": "",
+      "columns": {
+        "id": {
+          "name": "id",
+          "type": "uuid",
+          "primaryKey": true,
+          "notNull": true,
+          "default": "gen_random_uuid()"
+        },
+        "user_id": {
+          "name": "user_id",
+          "type": "uuid",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "name": {
+          "name": "name",
+          "type": "varchar(255)",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "front_template": {
+          "name": "front_template",
+          "type": "text",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "back_template": {
+          "name": "back_template",
+          "type": "text",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "is_reversible": {
+          "name": "is_reversible",
+          "type": "boolean",
+          "primaryKey": false,
+          "notNull": true,
+          "default": false
+        },
+        "created_at": {
+          "name": "created_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "updated_at": {
+          "name": "updated_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "deleted_at": {
+          "name": "deleted_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": false
+        },
+        "sync_version": {
+          "name": "sync_version",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        }
+      },
+      "indexes": {},
+      "foreignKeys": {
+        "note_types_user_id_users_id_fk": {
+          "name": "note_types_user_id_users_id_fk",
+          "tableFrom": "note_types",
+          "tableTo": "users",
+          "columnsFrom": [
+            "user_id"
+          ],
+          "columnsTo": [
+            "id"
+          ],
+          "onDelete": "no action",
+          "onUpdate": "no action"
+        }
+      },
+      "compositePrimaryKeys": {},
+      "uniqueConstraints": {},
+      "policies": {},
+      "checkConstraints": {},
+      "isRLSEnabled": false
+    },
+    "public.notes": {
+      "name": "notes",
+      "schema": "",
+      "columns": {
+        "id": {
+          "name": "id",
+          "type": "uuid",
+          "primaryKey": true,
+          "notNull": true,
+          "default": "gen_random_uuid()"
+        },
+        "deck_id": {
+          "name": "deck_id",
+          "type": "uuid",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "note_type_id": {
+          "name": "note_type_id",
+          "type": "uuid",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "created_at": {
+          "name": "created_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "updated_at": {
+          "name": "updated_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "deleted_at": {
+          "name": "deleted_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": false
+        },
+        "sync_version": {
+          "name": "sync_version",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        }
+      },
+      "indexes": {},
+      "foreignKeys": {
+        "notes_deck_id_decks_id_fk": {
+          "name": "notes_deck_id_decks_id_fk",
+          "tableFrom": "notes",
+          "tableTo": "decks",
+          "columnsFrom": [
+            "deck_id"
+          ],
+          "columnsTo": [
+            "id"
+          ],
+          "onDelete": "no action",
+          "onUpdate": "no action"
+        },
+        "notes_note_type_id_note_types_id_fk": {
+          "name": "notes_note_type_id_note_types_id_fk",
+          "tableFrom": "notes",
+          "tableTo": "note_types",
+          "columnsFrom": [
+            "note_type_id"
+          ],
+          "columnsTo": [
+            "id"
+          ],
+          "onDelete": "no action",
+          "onUpdate": "no action"
+        }
+      },
+      "compositePrimaryKeys": {},
+      "uniqueConstraints": {},
+      "policies": {},
+      "checkConstraints": {},
+      "isRLSEnabled": false
+    },
+    "public.refresh_tokens": {
+      "name": "refresh_tokens",
+      "schema": "",
+      "columns": {
+        "id": {
+          "name": "id",
+          "type": "uuid",
+          "primaryKey": true,
+          "notNull": true,
+          "default": "gen_random_uuid()"
+        },
+        "user_id": {
+          "name": "user_id",
+          "type": "uuid",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "token_hash": {
+          "name": "token_hash",
+          "type": "varchar(255)",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "expires_at": {
+          "name": "expires_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "created_at": {
+          "name": "created_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        }
+      },
+      "indexes": {},
+      "foreignKeys": {
+        "refresh_tokens_user_id_users_id_fk": {
+          "name": "refresh_tokens_user_id_users_id_fk",
+          "tableFrom": "refresh_tokens",
+          "tableTo": "users",
+          "columnsFrom": [
+            "user_id"
+          ],
+          "columnsTo": [
+            "id"
+          ],
+          "onDelete": "cascade",
+          "onUpdate": "no action"
+        }
+      },
+      "compositePrimaryKeys": {},
+      "uniqueConstraints": {},
+      "policies": {},
+      "checkConstraints": {},
+      "isRLSEnabled": false
+    },
+    "public.review_logs": {
+      "name": "review_logs",
+      "schema": "",
+      "columns": {
+        "id": {
+          "name": "id",
+          "type": "uuid",
+          "primaryKey": true,
+          "notNull": true,
+          "default": "gen_random_uuid()"
+        },
+        "card_id": {
+          "name": "card_id",
+          "type": "uuid",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "user_id": {
+          "name": "user_id",
+          "type": "uuid",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "rating": {
+          "name": "rating",
+          "type": "smallint",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "state": {
+          "name": "state",
+          "type": "smallint",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "scheduled_days": {
+          "name": "scheduled_days",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "elapsed_days": {
+          "name": "elapsed_days",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "reviewed_at": {
+          "name": "reviewed_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "duration_ms": {
+          "name": "duration_ms",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": false
+        },
+        "sync_version": {
+          "name": "sync_version",
+          "type": "integer",
+          "primaryKey": false,
+          "notNull": true,
+          "default": 0
+        }
+      },
+      "indexes": {},
+      "foreignKeys": {
+        "review_logs_card_id_cards_id_fk": {
+          "name": "review_logs_card_id_cards_id_fk",
+          "tableFrom": "review_logs",
+          "tableTo": "cards",
+          "columnsFrom": [
+            "card_id"
+          ],
+          "columnsTo": [
+            "id"
+          ],
+          "onDelete": "no action",
+          "onUpdate": "no action"
+        },
+        "review_logs_user_id_users_id_fk": {
+          "name": "review_logs_user_id_users_id_fk",
+          "tableFrom": "review_logs",
+          "tableTo": "users",
+          "columnsFrom": [
+            "user_id"
+          ],
+          "columnsTo": [
+            "id"
+          ],
+          "onDelete": "no action",
+          "onUpdate": "no action"
+        }
+      },
+      "compositePrimaryKeys": {},
+      "uniqueConstraints": {},
+      "policies": {},
+      "checkConstraints": {},
+      "isRLSEnabled": false
+    },
+    "public.users": {
+      "name": "users",
+      "schema": "",
+      "columns": {
+        "id": {
+          "name": "id",
+          "type": "uuid",
+          "primaryKey": true,
+          "notNull": true,
+          "default": "gen_random_uuid()"
+        },
+        "username": {
+          "name": "username",
+          "type": "varchar(255)",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "password_hash": {
+          "name": "password_hash",
+          "type": "varchar(255)",
+          "primaryKey": false,
+          "notNull": true
+        },
+        "created_at": {
+          "name": "created_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        },
+        "updated_at": {
+          "name": "updated_at",
+          "type": "timestamp with time zone",
+          "primaryKey": false,
+          "notNull": true,
+          "default": "now()"
+        }
+      },
+      "indexes": {},
+      "foreignKeys": {},
+      "compositePrimaryKeys": {},
+      "uniqueConstraints": {
+        "users_username_unique": {
+          "name": "users_username_unique",
+          "nullsNotDistinct": false,
+          "columns": [
+            "username"
+          ]
+        }
+      },
+      "policies": {},
+      "checkConstraints": {},
+      "isRLSEnabled": false
+    }
+  },
+  "enums": {},
+  "schemas": {},
+  "sequences": {},
+  "roles": {},
+  "policies": {},
+  "views": {},
+  "_meta": {
+    "columns": {},
+    "schemas": {},
+    "tables": {}
+  }
+}
\ No newline at end of file
diff --git a/drizzle/meta/_journal.json b/drizzle/meta/_journal.json
index 5da2908..cdfca60 100644
--- a/drizzle/meta/_journal.json
+++ b/drizzle/meta/_journal.json
@@ -22,6 +22,13 @@
       "when": 1767108756805,
       "tag": "0002_married_moondragon",
       "breakpoints": true
+    },
+    {
+      "idx": 3,
+      "version": "7",
+      "when": 1767156818092,
+      "tag": "0003_brave_blacklash",
+      "breakpoints": true
     }
   ]
 }
\ No newline at end of file
diff --git a/src/client/components/DeleteNoteModal.test.tsx b/src/client/components/DeleteNoteModal.test.tsx
index 85aaa14..a17323a 100644
--- a/src/client/components/DeleteNoteModal.test.tsx
+++ b/src/client/components/DeleteNoteModal.test.tsx
@@ -175,7 +175,7 @@ describe("DeleteNoteModal", () => {
 		const user = userEvent.setup();
 
 		// Create a promise that we can control
-		let resolveDelete: (value: unknown) => void;
+		let resolveDelete: ((value: unknown) => void) | undefined;
 		const deletePromise = new Promise((resolve) => {
 			resolveDelete = resolve;
 		});
@@ -190,19 +190,17 @@ describe("DeleteNoteModal", () => {
 		expect(screen.getByText("Deleting...")).toBeDefined();
 
 		// Resolve the delete request to cleanup
-		if (resolveDelete) {
-			resolveDelete({
-				ok: true,
-				json: async () => ({ success: true }),
-			});
-		}
+		resolveDelete?.({
+			ok: true,
+			json: async () => ({ success: true }),
+		});
 	});
 
 	it("disables buttons while deleting", async () => {
 		const user = userEvent.setup();
 
 		// Create a promise that we can control
-		let resolveDelete: (value: unknown) => void;
+		let resolveDelete: ((value: unknown) => void) | undefined;
 		const deletePromise = new Promise((resolve) => {
 			resolveDelete = resolve;
 		});
@@ -224,11 +222,9 @@ describe("DeleteNoteModal", () => {
 		);
 
 		// Resolve the delete request to cleanup
-		if (resolveDelete) {
-			resolveDelete({
-				ok: true,
-				json: async () => ({ success: true }),
-			});
-		}
+		resolveDelete?.({
+			ok: true,
+			json: async () => ({ success: true }),
+		});
 	});
 });
diff --git a/src/client/db/index.test.ts b/src/client/db/index.test.ts
index a30f94b..0a4882d 100644
--- a/src/client/db/index.test.ts
+++ b/src/client/db/index.test.ts
@@ -132,8 +132,8 @@ describe("KiokuDatabase", () => {
 		const testCard: LocalCard = {
 			id: "card-1",
 			deckId: "deck-1",
-			noteId: null,
-			isReversed: null,
+			noteId: "test-note-id",
+			isReversed: false,
 			front: "Question",
 			back: "Answer",
 			state: CardState.New,
diff --git a/src/client/db/index.ts b/src/client/db/index.ts
index 5318b17..53df476 100644
--- a/src/client/db/index.ts
+++ b/src/client/db/index.ts
@@ -122,8 +122,8 @@ export interface LocalNoteFieldValue {
 export interface LocalCard {
 	id: string;
 	deckId: string;
-	noteId: string | null;
-	isReversed: boolean | null;
+	noteId: string;
+	isReversed: boolean;
 	front: string;
 	back: string;
 
@@ -241,6 +241,18 @@ export class KiokuDatabase extends Dexie {
 						}
 					});
 			});
+
+		// Version 3: noteId and isReversed are now required (NOT NULL)
+		// No migration needed as production has no legacy data without notes
+		this.version(3).stores({
+			decks: "id, userId, updatedAt",
+			cards: "id, deckId, noteId, updatedAt, due, state",
+			reviewLogs: "id, cardId, userId, reviewedAt",
+			noteTypes: "id, userId, updatedAt",
+			noteFieldTypes: "id, noteTypeId, updatedAt",
+			notes: "id, deckId, noteTypeId, updatedAt",
+			noteFieldValues: "id, noteId, noteFieldTypeId, updatedAt",
+		});
 	}
 }
 
diff --git a/src/client/db/repositories.test.ts b/src/client/db/repositories.test.ts
index 2fca210..da0f0d3 100644
--- a/src/client/db/repositories.test.ts
+++ b/src/client/db/repositories.test.ts
@@ -240,6 +240,8 @@ describe("localCardRepository", () => {
 		it("should create a card with FSRS defaults", async () => {
 			const card = await localCardRepository.create({
 				deckId,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Question",
 				back: "Answer",
 			});
@@ -260,8 +262,8 @@ describe("localCardRepository", () => {
 
 	describe("findByDeckId", () => {
 		it("should return all cards for a deck", async () => {
-			await localCardRepository.create({ deckId, front: "Q1", back: "A1" });
-			await localCardRepository.create({ deckId, front: "Q2", back: "A2" });
+			await localCardRepository.create({ deckId, noteId: "test-note-id", isReversed: false, front: "Q1", back: "A1" });
+			await localCardRepository.create({ deckId, noteId: "test-note-id-2", isReversed: false, front: "Q2", back: "A2" });
 
 			const cards = await localCardRepository.findByDeckId(deckId);
 			expect(cards).toHaveLength(2);
@@ -270,6 +272,8 @@ describe("localCardRepository", () => {
 		it("should exclude soft-deleted cards", async () => {
 			const card = await localCardRepository.create({
 				deckId,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Q",
 				back: "A",
 			});
@@ -287,6 +291,8 @@ describe("localCardRepository", () => {
 
 			const card1 = await localCardRepository.create({
 				deckId,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Due",
 				back: "A",
 			});
@@ -294,6 +300,8 @@ describe("localCardRepository", () => {
 
 			const card2 = await localCardRepository.create({
 				deckId,
+				noteId: "test-note-id-2",
+				isReversed: false,
 				front: "Not Due",
 				back: "B",
 			});
@@ -308,6 +316,8 @@ describe("localCardRepository", () => {
 			for (let i = 0; i < 5; i++) {
 				await localCardRepository.create({
 					deckId,
+					noteId: `test-note-id-${i}`,
+					isReversed: false,
 					front: `Q${i}`,
 					back: `A${i}`,
 				});
@@ -322,12 +332,16 @@ describe("localCardRepository", () => {
 		it("should return only new cards", async () => {
 			await localCardRepository.create({
 				deckId,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "New",
 				back: "A",
 			});
 
 			const reviewedCard = await localCardRepository.create({
 				deckId,
+				noteId: "test-note-id-2",
+				isReversed: false,
 				front: "Reviewed",
 				back: "B",
 			});
@@ -343,6 +357,8 @@ describe("localCardRepository", () => {
 		it("should update card content", async () => {
 			const card = await localCardRepository.create({
 				deckId,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Original",
 				back: "Original",
 			});
@@ -362,6 +378,8 @@ describe("localCardRepository", () => {
 		it("should update FSRS scheduling data", async () => {
 			const card = await localCardRepository.create({
 				deckId,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Q",
 				back: "A",
 			});
@@ -391,6 +409,8 @@ describe("localCardRepository", () => {
 		it("should soft delete a card", async () => {
 			const card = await localCardRepository.create({
 				deckId,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Q",
 				back: "A",
 			});
@@ -423,6 +443,8 @@ describe("localReviewLogRepository", () => {
 
 		const card = await localCardRepository.create({
 			deckId,
+			noteId: "test-note-id",
+			isReversed: false,
 			front: "Q",
 			back: "A",
 		});
diff --git a/src/client/db/repositories.ts b/src/client/db/repositories.ts
index 104f026..e01254e 100644
--- a/src/client/db/repositories.ts
+++ b/src/client/db/repositories.ts
@@ -176,8 +176,6 @@ export const localCardRepository = {
 		data: Omit<
 			LocalCard,
 			| "id"
-			| "noteId"
-			| "isReversed"
 			| "state"
 			| "due"
 			| "stability"
@@ -192,14 +190,11 @@ export const localCardRepository = {
 			| "deletedAt"
 			| "syncVersion"
 			| "_synced"
-		> &
-			Partial<Pick<LocalCard, "noteId" | "isReversed">>,
+		>,
 	): Promise<LocalCard> {
 		const now = new Date();
 		const card: LocalCard = {
 			id: uuidv4(),
-			noteId: null,
-			isReversed: null,
 			...data,
 			state: CardState.New,
 			due: now,
diff --git a/src/client/pages/DeckDetailPage.test.tsx b/src/client/pages/DeckDetailPage.test.tsx
index 35303d9..e02302f 100644
--- a/src/client/pages/DeckDetailPage.test.tsx
+++ b/src/client/pages/DeckDetailPage.test.tsx
@@ -51,13 +51,13 @@ const mockDeck = {
 	updatedAt: "2024-01-01T00:00:00Z",
 };
 
-// Legacy cards (no noteId) for backward compatibility testing
-const mockLegacyCards = [
+// Basic note-based cards (each with its own note)
+const mockBasicCards = [
 	{
 		id: "card-1",
 		deckId: "deck-1",
-		noteId: null,
-		isReversed: null,
+		noteId: "note-1",
+		isReversed: false,
 		front: "Hello",
 		back: "こんにちは",
 		state: 0,
@@ -77,8 +77,8 @@ const mockLegacyCards = [
 	{
 		id: "card-2",
 		deckId: "deck-1",
-		noteId: null,
-		isReversed: null,
+		noteId: "note-2",
+		isReversed: false,
 		front: "Goodbye",
 		back: "さようなら",
 		state: 2,
@@ -143,11 +143,8 @@ const mockNoteBasedCards = [
 	},
 ];
 
-// Mixed cards (both legacy and note-based)
-const mockMixedCards = [...mockLegacyCards, ...mockNoteBasedCards];
-
-// Alias for backward compatibility in existing tests
-const mockCards = mockLegacyCards;
+// Alias for existing tests
+const mockCards = mockBasicCards;
 
 function renderWithProviders(path = "/decks/deck-1") {
 	const { hook } = memoryLocation({ path, static: true });
@@ -430,8 +427,8 @@ describe("DeckDetailPage", () => {
 		expect(screen.queryByText("Common Japanese words")).toBeNull();
 	});
 
-	describe("Delete Card", () => {
-		it("shows Delete button for each card", async () => {
+	describe("Delete Note", () => {
+		it("shows Delete button for each note", async () => {
 			mockFetch
 				.mockResolvedValueOnce({
 					ok: true,
@@ -449,7 +446,7 @@ describe("DeckDetailPage", () => {
 			});
 
 			const deleteButtons = screen.getAllByRole("button", {
-				name: "Delete card",
+				name: "Delete note",
 			});
 			expect(deleteButtons.length).toBe(2);
 		});
@@ -474,7 +471,7 @@ describe("DeckDetailPage", () => {
 			});
 
 			const deleteButtons = screen.getAllByRole("button", {
-				name: "Delete card",
+				name: "Delete note",
 			});
 			const firstDeleteButton = deleteButtons[0];
 			if (firstDeleteButton) {
@@ -483,7 +480,7 @@ describe("DeckDetailPage", () => {
 
 			expect(screen.getByRole("dialog")).toBeDefined();
 			expect(
-				screen.getByRole("heading", { name: "Delete Card" }),
+				screen.getByRole("heading", { name: "Delete Note" }),
 			).toBeDefined();
 		});
 
@@ -507,7 +504,7 @@ describe("DeckDetailPage", () => {
 			});
 
 			const deleteButtons = screen.getAllByRole("button", {
-				name: "Delete card",
+				name: "Delete note",
 			});
 			const firstDeleteButton = deleteButtons[0];
 			if (firstDeleteButton) {
@@ -521,7 +518,7 @@ describe("DeckDetailPage", () => {
 			expect(screen.queryByRole("dialog")).toBeNull();
 		});
 
-		it("deletes card and refreshes list on confirmation", async () => {
+		it("deletes note and refreshes list on confirmation", async () => {
 			const user = userEvent.setup();
 
 			mockFetch
@@ -537,7 +534,7 @@ describe("DeckDetailPage", () => {
 				// Delete request
 				.mockResolvedValueOnce({
 					ok: true,
-					json: async () => ({}),
+					json: async () => ({ success: true }),
 				})
 				// Refresh cards after deletion
 				.mockResolvedValueOnce({
@@ -552,7 +549,7 @@ describe("DeckDetailPage", () => {
 			});
 
 			const deleteButtons = screen.getAllByRole("button", {
-				name: "Delete card",
+				name: "Delete note",
 			});
 			const firstDeleteButton = deleteButtons[0];
 			if (firstDeleteButton) {
@@ -575,8 +572,8 @@ describe("DeckDetailPage", () => {
 				expect(screen.queryByRole("dialog")).toBeNull();
 			});
 
-			// Verify DELETE request was made
-			expect(mockFetch).toHaveBeenCalledWith("/api/decks/deck-1/cards/card-1", {
+			// Verify DELETE request was made to notes endpoint
+			expect(mockFetch).toHaveBeenCalledWith("/api/decks/deck-1/notes/note-1", {
 				method: "DELETE",
 				headers: { Authorization: "Bearer access-token" },
 			});
@@ -604,7 +601,7 @@ describe("DeckDetailPage", () => {
 				.mockResolvedValueOnce({
 					ok: false,
 					status: 500,
-					json: async () => ({ error: "Failed to delete card" }),
+					json: async () => ({ error: "Failed to delete note" }),
 				});
 
 			renderWithProviders();
@@ -614,7 +611,7 @@ describe("DeckDetailPage", () => {
 			});
 
 			const deleteButtons = screen.getAllByRole("button", {
-				name: "Delete card",
+				name: "Delete note",
 			});
 			const firstDeleteButton = deleteButtons[0];
 			if (firstDeleteButton) {
@@ -635,7 +632,7 @@ describe("DeckDetailPage", () => {
 			// Error should be displayed in the modal
 			await waitFor(() => {
 				expect(screen.getByRole("alert").textContent).toContain(
-					"Failed to delete card",
+					"Failed to delete note",
 				);
 			});
 		});
@@ -665,32 +662,6 @@ describe("DeckDetailPage", () => {
 			expect(noteCards.length).toBe(2);
 		});
 
-		it("displays legacy cards separately from note groups", async () => {
-			mockFetch
-				.mockResolvedValueOnce({
-					ok: true,
-					json: async () => ({ deck: mockDeck }),
-				})
-				.mockResolvedValueOnce({
-					ok: true,
-					json: async () => ({ cards: mockMixedCards }),
-				});
-
-			renderWithProviders();
-
-			await waitFor(() => {
-				// Should show both note groups and legacy cards
-				expect(screen.getByTestId("note-group")).toBeDefined();
-			});
-
-			const legacyCards = screen.getAllByTestId("legacy-card");
-			expect(legacyCards.length).toBe(2); // 2 legacy cards
-
-			// Should show "Legacy" badge for legacy cards
-			const legacyBadges = screen.getAllByText("Legacy");
-			expect(legacyBadges.length).toBe(2);
-		});
-
 		it("shows Normal and Reversed badges for note-based cards", async () => {
 			mockFetch
 				.mockResolvedValueOnce({
diff --git a/src/client/pages/DeckDetailPage.tsx b/src/client/pages/DeckDetailPage.tsx
index 87f9dc3..d018d1f 100644
--- a/src/client/pages/DeckDetailPage.tsx
+++ b/src/client/pages/DeckDetailPage.tsx
@@ -21,8 +21,8 @@ import { EditNoteModal } from "../components/EditNoteModal";
 interface Card {
 	id: string;
 	deckId: string;
-	noteId: string | null;
-	isReversed: boolean | null;
+	noteId: string;
+	isReversed: boolean;
 	front: string;
 	back: string;
 	state: number;
@@ -33,10 +33,8 @@ interface Card {
 	updatedAt: string;
 }
 
-/** Combined type for display: either a note group or a legacy card */
-type CardDisplayItem =
-	| { type: "note"; noteId: string; cards: Card[] }
-	| { type: "legacy"; card: Card };
+/** Combined type for display: note group */
+type CardDisplayItem = { type: "note"; noteId: string; cards: Card[] };
 
 interface Deck {
 	id: string;
@@ -178,95 +176,6 @@ function NoteGroupCard({
 	);
 }
 
-/** Component for displaying a legacy card (without note association) */
-function LegacyCardItem({
-	card,
-	index,
-	onEdit,
-	onDelete,
-}: {
-	card: Card;
-	index: number;
-	onEdit: () => void;
-	onDelete: () => void;
-}) {
-	return (
-		<div
-			data-testid="legacy-card"
-			className="bg-white rounded-xl border border-border/50 p-5 shadow-card hover:shadow-md transition-all duration-200"
-			style={{ animationDelay: `${index * 30}ms` }}
-		>
-			<div className="flex items-start justify-between gap-4">
-				<div className="flex-1 min-w-0">
-					{/* Front/Back Preview */}
-					<div className="grid grid-cols-2 gap-4 mb-3">
-						<div>
-							<span className="text-xs font-medium text-muted uppercase tracking-wide">
-								Front
-							</span>
-							<p className="mt-1 text-slate text-sm line-clamp-2 whitespace-pre-wrap break-words">
-								{card.front}
-							</p>
-						</div>
-						<div>
-							<span className="text-xs font-medium text-muted uppercase tracking-wide">
-								Back
-							</span>
-							<p className="mt-1 text-slate text-sm line-clamp-2 whitespace-pre-wrap break-words">
-								{card.back}
-							</p>
-						</div>
-					</div>
-
-					{/* Card Stats */}
-					<div className="flex items-center gap-3 text-xs">
-						<span
-							className={`px-2 py-0.5 rounded-full font-medium ${CardStateColors[card.state] || "bg-muted/10 text-muted"}`}
-						>
-							{CardStateLabels[card.state] || "Unknown"}
-						</span>
-						<span className="px-2 py-0.5 rounded-full font-medium bg-amber-100 text-amber-700">
-							Legacy
-						</span>
-						<span className="text-muted">{card.reps} reviews</span>
-						{card.lapses > 0 && (
-							<span className="text-muted">{card.lapses} lapses</span>
-						)}
-					</div>
-				</div>
-
-				{/* Actions */}
-				<div className="flex items-center gap-1 shrink-0">
-					<button
-						type="button"
-						onClick={onEdit}
-						className="p-2 text-muted hover:text-slate hover:bg-ivory rounded-lg transition-colors"
-						title="Edit card"
-					>
-						<FontAwesomeIcon
-							icon={faPen}
-							className="w-4 h-4"
-							aria-hidden="true"
-						/>
-					</button>
-					<button
-						type="button"
-						onClick={onDelete}
-						className="p-2 text-muted hover:text-error hover:bg-error/5 rounded-lg transition-colors"
-						title="Delete card"
-					>
-						<FontAwesomeIcon
-							icon={faTrash}
-							className="w-4 h-4"
-							aria-hidden="true"
-						/>
-					</button>
-				</div>
-			</div>
-		</div>
-	);
-}
-
 export function DeckDetailPage() {
 	const { deckId } = useParams<{ deckId: string }>();
 	const [deck, setDeck] = useState<Deck | null>(null);
@@ -282,24 +191,17 @@ export function DeckDetailPage() {
 	// Group cards by note for display
 	const displayItems = useMemo((): CardDisplayItem[] => {
 		const noteGroups = new Map<string, Card[]>();
-		const legacyCards: Card[] = [];
 
 		for (const card of cards) {
-			if (card.noteId) {
-				const existing = noteGroups.get(card.noteId);
-				if (existing) {
-					existing.push(card);
-				} else {
-					noteGroups.set(card.noteId, [card]);
-				}
+			const existing = noteGroups.get(card.noteId);
+			if (existing) {
+				existing.push(card);
 			} else {
-				legacyCards.push(card);
+				noteGroups.set(card.noteId, [card]);
 			}
 		}
 
-		const items: CardDisplayItem[] = [];
-
-		// Add note groups first, sorted by earliest card creation
+		// Sort note groups by earliest card creation (newest first)
 		const sortedNoteGroups = Array.from(noteGroups.entries()).sort(
 			([, cardsA], [, cardsB]) => {
 				const minA = Math.min(
@@ -312,6 +214,7 @@ export function DeckDetailPage() {
 			},
 		);
 
+		const items: CardDisplayItem[] = [];
 		for (const [noteId, noteCards] of sortedNoteGroups) {
 			// Sort cards within group: normal first, then reversed
 			noteCards.sort((a, b) => {
@@ -321,15 +224,6 @@ export function DeckDetailPage() {
 			items.push({ type: "note", noteId, cards: noteCards });
 		}
 
-		// Add legacy cards, newest first
-		legacyCards.sort(
-			(a, b) =>
-				new Date(b.createdAt).getTime() - new Date(a.createdAt).getTime(),
-		);
-		for (const card of legacyCards) {
-			items.push({ type: "legacy", card });
-		}
-
 		return items;
 	}, [cards]);
 
@@ -551,26 +445,16 @@ export function DeckDetailPage() {
 						{/* Card List - Grouped by Note */}
 						{cards.length > 0 && (
 							<div className="space-y-4">
-								{displayItems.map((item, index) =>
-									item.type === "note" ? (
-										<NoteGroupCard
-											key={item.noteId}
-											noteId={item.noteId}
-											cards={item.cards}
-											index={index}
-											onEditNote={() => setEditingNoteId(item.noteId)}
-											onDeleteNote={() => setDeletingNoteId(item.noteId)}
-										/>
-									) : (
-										<LegacyCardItem
-											key={item.card.id}
-											card={item.card}
-											index={index}
-											onEdit={() => setEditingCard(item.card)}
-											onDelete={() => setDeletingCard(item.card)}
-										/>
-									),
-								)}
+								{displayItems.map((item, index) => (
+									<NoteGroupCard
+										key={item.noteId}
+										noteId={item.noteId}
+										cards={item.cards}
+										index={index}
+										onEditNote={() => setEditingNoteId(item.noteId)}
+										onDeleteNote={() => setDeletingNoteId(item.noteId)}
+									/>
+								))}
 							</div>
 						)}
 					</div>
diff --git a/src/client/pages/StudyPage.tsx b/src/client/pages/StudyPage.tsx
index bdaf7e3..0eb5118 100644
--- a/src/client/pages/StudyPage.tsx
+++ b/src/client/pages/StudyPage.tsx
@@ -13,8 +13,8 @@ import { renderCard } from "../utils/templateRenderer";
 interface Card {
 	id: string;
 	deckId: string;
-	noteId: string | null;
-	isReversed: boolean | null;
+	noteId: string;
+	isReversed: boolean;
 	front: string;
 	back: string;
 	state: number;
@@ -23,11 +23,11 @@ interface Card {
 	difficulty: number;
 	reps: number;
 	lapses: number;
-	/** Note type templates for rendering (null for legacy cards) */
+	/** Note type templates for rendering */
 	noteType: {
 		frontTemplate: string;
 		backTemplate: string;
-	} | null;
+	};
 	/** Field values as a name-value map for template rendering */
 	fieldValuesMap: Record<string, string>;
 }
diff --git a/src/client/sync/conflict.test.ts b/src/client/sync/conflict.test.ts
index 6a10c4f..52362ff 100644
--- a/src/client/sync/conflict.test.ts
+++ b/src/client/sync/conflict.test.ts
@@ -271,6 +271,8 @@ describe("ConflictResolver", () => {
 
 			const localCard = await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Local Question",
 				back: "Local Answer",
 			});
@@ -278,6 +280,8 @@ describe("ConflictResolver", () => {
 			const serverCard = {
 				id: localCard.id,
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Server Question",
 				back: "Server Answer",
 				state: CardState.Review,
@@ -316,6 +320,8 @@ describe("ConflictResolver", () => {
 
 			const localCard = await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Local Question",
 				back: "Local Answer",
 			});
@@ -323,6 +329,8 @@ describe("ConflictResolver", () => {
 			const serverCard = {
 				id: localCard.id,
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Server Question",
 				back: "Server Answer",
 				state: CardState.New,
@@ -435,6 +443,8 @@ describe("ConflictResolver", () => {
 
 			const card = await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Local Question",
 				back: "Local Answer",
 			});
@@ -456,6 +466,8 @@ describe("ConflictResolver", () => {
 					{
 						id: card.id,
 						deckId: deck.id,
+						noteId: "test-note-id",
+						isReversed: false,
 						front: "Server Question",
 						back: "Server Answer",
 						state: CardState.New,
diff --git a/src/client/sync/conflict.ts b/src/client/sync/conflict.ts
index d9c3f55..2451920 100644
--- a/src/client/sync/conflict.ts
+++ b/src/client/sync/conflict.ts
@@ -91,8 +91,8 @@ function serverCardToLocal(card: ServerCard): LocalCard {
 	return {
 		id: card.id,
 		deckId: card.deckId,
-		noteId: card.noteId ?? null,
-		isReversed: card.isReversed ?? null,
+		noteId: card.noteId,
+		isReversed: card.isReversed,
 		front: card.front,
 		back: card.back,
 		state: card.state as LocalCard["state"],
diff --git a/src/client/sync/pull.test.ts b/src/client/sync/pull.test.ts
index 9ba678e..dd562a0 100644
--- a/src/client/sync/pull.test.ts
+++ b/src/client/sync/pull.test.ts
@@ -101,6 +101,8 @@ describe("pullResultToLocalData", () => {
 			{
 				id: "card-1",
 				deckId: "deck-1",
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Question",
 				back: "Answer",
 				state: CardState.Review,
@@ -130,8 +132,8 @@ describe("pullResultToLocalData", () => {
 		expect(result.cards[0]).toEqual({
 			id: "card-1",
 			deckId: "deck-1",
-			noteId: null,
-			isReversed: null,
+			noteId: "test-note-id",
+			isReversed: false,
 			front: "Question",
 			back: "Answer",
 			state: CardState.Review,
@@ -156,6 +158,8 @@ describe("pullResultToLocalData", () => {
 			{
 				id: "card-1",
 				deckId: "deck-1",
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "New Card",
 				back: "Answer",
 				state: CardState.New,
@@ -568,8 +572,8 @@ describe("PullService", () => {
 					{
 						id: "server-card-1",
 						deckId: deck.id,
-						noteId: null,
-						isReversed: null,
+						noteId: "test-note-id",
+						isReversed: false,
 						front: "Server Question",
 						back: "Server Answer",
 						state: CardState.New,
@@ -715,8 +719,8 @@ describe("PullService", () => {
 					{
 						id: "card-1",
 						deckId: "deck-1",
-						noteId: null,
-						isReversed: null,
+						noteId: "test-note-id",
+						isReversed: false,
 						front: "Q",
 						back: "A",
 						state: CardState.New,
diff --git a/src/client/sync/pull.ts b/src/client/sync/pull.ts
index 55c859c..8b55a9b 100644
--- a/src/client/sync/pull.ts
+++ b/src/client/sync/pull.ts
@@ -33,8 +33,8 @@ export interface ServerDeck {
 export interface ServerCard {
 	id: string;
 	deckId: string;
-	noteId?: string | null;
-	isReversed?: boolean | null;
+	noteId: string;
+	isReversed: boolean;
 	front: string;
 	back: string;
 	state: number;
@@ -172,8 +172,8 @@ function serverCardToLocal(card: ServerCard): LocalCard {
 	return {
 		id: card.id,
 		deckId: card.deckId,
-		noteId: card.noteId ?? null,
-		isReversed: card.isReversed ?? null,
+		noteId: card.noteId,
+		isReversed: card.isReversed,
 		front: card.front,
 		back: card.back,
 		state: card.state as CardStateType,
diff --git a/src/client/sync/push.test.ts b/src/client/sync/push.test.ts
index 9a42eff..16198c1 100644
--- a/src/client/sync/push.test.ts
+++ b/src/client/sync/push.test.ts
@@ -131,8 +131,8 @@ describe("pendingChangesToPushData", () => {
 			{
 				id: "card-1",
 				deckId: "deck-1",
-				noteId: null,
-				isReversed: null,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Question",
 				back: "Answer",
 				state: CardState.Review,
@@ -163,8 +163,8 @@ describe("pendingChangesToPushData", () => {
 		expect(result.cards[0]).toEqual({
 			id: "card-1",
 			deckId: "deck-1",
-			noteId: null,
-			isReversed: null,
+			noteId: "test-note-id",
+			isReversed: false,
 			front: "Question",
 			back: "Answer",
 			state: CardState.Review,
@@ -187,8 +187,8 @@ describe("pendingChangesToPushData", () => {
 			{
 				id: "card-1",
 				deckId: "deck-1",
-				noteId: null,
-				isReversed: null,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "New Card",
 				back: "Answer",
 				state: CardState.New,
@@ -566,6 +566,8 @@ describe("PushService", () => {
 
 			const card = await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Question",
 				back: "Answer",
 			});
@@ -611,6 +613,8 @@ describe("PushService", () => {
 
 			const card = await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Q",
 				back: "A",
 			});
@@ -740,6 +744,8 @@ describe("PushService", () => {
 
 			const card = await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Q",
 				back: "A",
 			});
diff --git a/src/client/sync/push.ts b/src/client/sync/push.ts
index f5c9275..b83136e 100644
--- a/src/client/sync/push.ts
+++ b/src/client/sync/push.ts
@@ -35,8 +35,8 @@ export interface SyncDeckData {
 export interface SyncCardData {
 	id: string;
 	deckId: string;
-	noteId: string | null;
-	isReversed: boolean | null;
+	noteId: string;
+	isReversed: boolean;
 	front: string;
 	back: string;
 	state: number;
diff --git a/src/client/sync/queue.test.ts b/src/client/sync/queue.test.ts
index 2038e0d..e815282 100644
--- a/src/client/sync/queue.test.ts
+++ b/src/client/sync/queue.test.ts
@@ -85,6 +85,8 @@ describe("SyncQueue", () => {
 			});
 			await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Question",
 				back: "Answer",
 			});
@@ -103,6 +105,8 @@ describe("SyncQueue", () => {
 			});
 			const card = await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Question",
 				back: "Answer",
 			});
@@ -145,11 +149,15 @@ describe("SyncQueue", () => {
 			});
 			await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id-1",
+				isReversed: false,
 				front: "Q1",
 				back: "A1",
 			});
 			await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id-2",
+				isReversed: false,
 				front: "Q2",
 				back: "A2",
 			});
@@ -323,6 +331,8 @@ describe("SyncQueue", () => {
 			});
 			const card = await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Q",
 				back: "A",
 			});
@@ -351,6 +361,8 @@ describe("SyncQueue", () => {
 			});
 			const card = await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Q",
 				back: "A",
 			});
@@ -440,8 +452,8 @@ describe("SyncQueue", () => {
 			const serverCard = {
 				id: "server-card-1",
 				deckId: deck.id,
-				noteId: null,
-				isReversed: null,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Server Question",
 				back: "Server Answer",
 				state: CardState.New,
@@ -484,6 +496,8 @@ describe("SyncQueue", () => {
 			});
 			const card = await localCardRepository.create({
 				deckId: deck.id,
+				noteId: "test-note-id",
+				isReversed: false,
 				front: "Q",
 				back: "A",
 			});
diff --git a/src/server/db/schema.ts b/src/server/db/schema.ts
index bd3d396..0471a92 100644
--- a/src/server/db/schema.ts
+++ b/src/server/db/schema.ts
@@ -153,8 +153,10 @@ export const cards = pgTable("cards", {
 	deckId: uuid("deck_id")
 		.notNull()
 		.references(() => decks.id),
-	noteId: uuid("note_id").references(() => notes.id),
-	isReversed: boolean("is_reversed"),
+	noteId: uuid("note_id")
+		.notNull()
+		.references(() => notes.id),
+	isReversed: boolean("is_reversed").notNull(),
 	front: text("front").notNull(),
 	back: text("back").notNull(),
 
diff --git a/src/server/repositories/card.test.ts b/src/server/repositories/card.test.ts
index 9d7ffa6..98913e9 100644
--- a/src/server/repositories/card.test.ts
+++ b/src/server/repositories/card.test.ts
@@ -12,8 +12,8 @@ function createMockCard(overrides: Partial<Card> = {}): Card {
 	return {
 		id: "card-uuid-123",
 		deckId: "deck-uuid-123",
-		noteId: null,
-		isReversed: null,
+		noteId: "note-uuid-123",
+		isReversed: false,
 		front: "Front text",
 		back: "Back text",
 		state: 0,
@@ -89,15 +89,14 @@ function createMockCardWithNoteData(
 function createMockCardForStudy(
 	overrides: Partial<CardForStudy> = {},
 ): CardForStudy {
-	const card = createMockCard({
-		noteId: overrides.noteType ? "note-uuid-123" : null,
-		isReversed: overrides.noteType ? false : null,
-		...overrides,
-	});
+	const card = createMockCard(overrides);
 	return {
 		...card,
-		noteType: overrides.noteType ?? null,
-		fieldValuesMap: overrides.fieldValuesMap ?? {},
+		noteType: overrides.noteType ?? {
+			frontTemplate: "{{Front}}",
+			backTemplate: "{{Back}}",
+		},
+		fieldValuesMap: overrides.fieldValuesMap ?? { Front: "Q", Back: "A" },
 	};
 }
 
@@ -125,8 +124,8 @@ describe("CardRepository mock factory", () => {
 
 			expect(card.id).toBe("card-uuid-123");
 			expect(card.deckId).toBe("deck-uuid-123");
-			expect(card.noteId).toBeNull();
-			expect(card.isReversed).toBeNull();
+			expect(card.noteId).toBe("note-uuid-123");
+			expect(card.isReversed).toBe(false);
 			expect(card.front).toBe("Front text");
 			expect(card.back).toBe("Back text");
 			expect(card.state).toBe(0);
@@ -205,17 +204,13 @@ describe("CardRepository mock factory", () => {
 			expect(cardWithNote.fieldValues[0]?.value).toBe("日本語");
 		});
 
-		it("can represent legacy card with null note", () => {
-			// For legacy cards without notes, we explicitly construct the type
-			const legacyCard: CardWithNoteData = {
-				...createMockCard({ noteId: null, isReversed: null }),
-				note: null,
-				fieldValues: [],
-			};
-
-			expect(legacyCard.noteId).toBeNull();
-			expect(legacyCard.note).toBeNull();
-			expect(legacyCard.fieldValues).toHaveLength(0);
+		it("card always has note association", () => {
+			// All cards now require note association
+			const cardWithNote = createMockCardWithNoteData();
+
+			expect(cardWithNote.noteId).toBe("note-uuid-123");
+			expect(cardWithNote.note).not.toBeNull();
+			expect(cardWithNote.fieldValues).toHaveLength(2);
 		});
 	});
 
@@ -392,41 +387,39 @@ describe("Card interface contracts", () => {
 		expect(cardForStudy.fieldValuesMap.Front).toBe("Question");
 	});
 
-	it("CardForStudy can represent legacy card with null noteType", () => {
-		const legacyCard = createMockCardForStudy({
-			front: "Legacy Question",
-			back: "Legacy Answer",
+	it("CardForStudy has required note data", () => {
+		const cardForStudy = createMockCardForStudy({
+			front: "Question",
+			back: "Answer",
 		});
 
-		expect(legacyCard.noteId).toBeNull();
-		expect(legacyCard.noteType).toBeNull();
-		expect(legacyCard.fieldValuesMap).toEqual({});
-		expect(legacyCard.front).toBe("Legacy Question");
-		expect(legacyCard.back).toBe("Legacy Answer");
+		expect(cardForStudy.noteId).toBe("note-uuid-123");
+		expect(cardForStudy.noteType).not.toBeNull();
+		expect(cardForStudy.noteType.frontTemplate).toBe("{{Front}}");
+		expect(cardForStudy.fieldValuesMap).toEqual({ Front: "Q", Back: "A" });
 	});
 });
 
 describe("Card and Note relationship", () => {
-	it("legacy card has null noteId and isReversed", () => {
+	it("card has required noteId and isReversed", () => {
 		const card = createMockCard();
 
-		expect(card.noteId).toBeNull();
-		expect(card.isReversed).toBeNull();
+		expect(card.noteId).toBe("note-uuid-123");
+		expect(card.isReversed).toBe(false);
 	});
 
-	it("note-based card has noteId and isReversed set", () => {
+	it("card with explicit note data", () => {
 		const card = createMockCard({
-			noteId: "note-uuid-123",
+			noteId: "different-note-id",
 			isReversed: false,
 		});
 
-		expect(card.noteId).toBe("note-uuid-123");
+		expect(card.noteId).toBe("different-note-id");
 		expect(card.isReversed).toBe(false);
 	});
 
 	it("reversed card has isReversed true", () => {
 		const card = createMockCard({
-			noteId: "note-uuid-123",
 			isReversed: true,
 		});
 
diff --git a/src/server/repositories/card.ts b/src/server/repositories/card.ts
index 7116642..4c4fc81 100644
--- a/src/server/repositories/card.ts
+++ b/src/server/repositories/card.ts
@@ -47,20 +47,15 @@ export const cardRepository: CardRepository = {
 			return undefined;
 		}
 
-		if (!card.noteId) {
-			return {
-				...card,
-				note: null,
-				fieldValues: [],
-			};
-		}
-
 		const noteResult = await db
 			.select()
 			.from(notes)
 			.where(and(eq(notes.id, card.noteId), isNull(notes.deletedAt)));
 
-		const note = noteResult[0] ?? null;
+		const note = noteResult[0];
+		if (!note) {
+			return undefined;
+		}
 
 		const fieldValuesResult = await db
 			.select()
@@ -85,6 +80,8 @@ export const cardRepository: CardRepository = {
 	async create(
 		deckId: string,
 		data: {
+			noteId: string;
+			isReversed: boolean;
 			front: string;
 			back: string;
 		},
@@ -93,6 +90,8 @@ export const cardRepository: CardRepository = {
 			.insert(cards)
 			.values({
 				deckId,
+				noteId: data.noteId,
+				isReversed: data.isReversed,
 				front: data.front,
 				back: data.back,
 				state: CardState.New,
@@ -200,21 +199,16 @@ export const cardRepository: CardRepository = {
 		const cardsWithNoteData: CardWithNoteData[] = [];
 
 		for (const card of dueCards) {
-			if (!card.noteId) {
-				cardsWithNoteData.push({
-					...card,
-					note: null,
-					fieldValues: [],
-				});
-				continue;
-			}
-
 			const noteResult = await db
 				.select()
 				.from(notes)
 				.where(and(eq(notes.id, card.noteId), isNull(notes.deletedAt)));
 
-			const note = noteResult[0] ?? null;
+			const note = noteResult[0];
+			if (!note) {
+				// Note was deleted, skip this card
+				continue;
+			}
 
 			const fieldValuesResult = await db
 				.select()
@@ -241,16 +235,6 @@ export const cardRepository: CardRepository = {
 		const cardsForStudy: CardForStudy[] = [];
 
 		for (const card of dueCards) {
-			// Legacy card (no note association)
-			if (!card.noteId) {
-				cardsForStudy.push({
-					...card,
-					noteType: null,
-					fieldValuesMap: {},
-				});
-				continue;
-			}
-
 			// Fetch note to get noteTypeId
 			const noteResult = await db
 				.select()
@@ -259,12 +243,7 @@ export const cardRepository: CardRepository = {
 
 			const note = noteResult[0];
 			if (!note) {
-				// Note was deleted, treat as legacy card
-				cardsForStudy.push({
-					...card,
-					noteType: null,
-					fieldValuesMap: {},
-				});
+				// Note was deleted, skip this card
 				continue;
 			}
 
@@ -281,12 +260,7 @@ export const cardRepository: CardRepository = {
 
 			const noteType = noteTypeResult[0];
 			if (!noteType) {
-				// Note type was deleted, treat as legacy card
-				cardsForStudy.push({
-					...card,
-					noteType: null,
-					fieldValuesMap: {},
-				});
+				// Note type was deleted, skip this card
 				continue;
 			}
 
diff --git a/src/server/repositories/note.test.ts b/src/server/repositories/note.test.ts
index 70dcb4a..cc1a9ae 100644
--- a/src/server/repositories/note.test.ts
+++ b/src/server/repositories/note.test.ts
@@ -40,8 +40,8 @@ function createMockCard(overrides: Partial<Card> = {}): Card {
 	return {
 		id: "card-uuid-123",
 		deckId: "deck-uuid-123",
-		noteId: null,
-		isReversed: null,
+		noteId: "note-uuid-123",
+		isReversed: false,
 		front: "Front text",
 		back: "Back text",
 		state: 0,
diff --git a/src/server/repositories/sync.ts b/src/server/repositories/sync.ts
index 8c4fd25..59a195a 100644
--- a/src/server/repositories/sync.ts
+++ b/src/server/repositories/sync.ts
@@ -45,8 +45,8 @@ export interface SyncDeckData {
 export interface SyncCardData {
 	id: string;
 	deckId: string;
-	noteId: string | null;
-	isReversed: boolean | null;
+	noteId: string;
+	isReversed: boolean;
 	front: string;
 	back: string;
 	state: number;
diff --git a/src/server/repositories/types.ts b/src/server/repositories/types.ts
index c864be0..a986cad 100644
--- a/src/server/repositories/types.ts
+++ b/src/server/repositories/types.ts
@@ -81,8 +81,8 @@ export interface DeckRepository {
 export interface Card {
 	id: string;
 	deckId: string;
-	noteId: string | null;
-	isReversed: boolean | null;
+	noteId: string;
+	isReversed: boolean;
 	front: string;
 	back: string;
 
@@ -104,22 +104,20 @@ export interface Card {
 }
 
 export interface CardWithNoteData extends Card {
-	note: Note | null;
+	note: Note;
 	fieldValues: NoteFieldValue[];
 }
 
 /**
  * Card data prepared for study, including all necessary template rendering info.
- * For note-based cards, includes templates and field values as a name-value map.
- * For legacy cards, note and templates are null.
  */
 export interface CardForStudy extends Card {
-	/** Note type templates for rendering (null for legacy cards) */
+	/** Note type templates for rendering */
 	noteType: {
 		frontTemplate: string;
 		backTemplate: string;
-	} | null;
-	/** Field values as a name-value map for template rendering (empty for legacy cards) */
+	};
+	/** Field values as a name-value map for template rendering */
 	fieldValuesMap: Record<string, string>;
 }
 
diff --git a/src/server/routes/cards.test.ts b/src/server/routes/cards.test.ts
index 780ea44..66ba601 100644
--- a/src/server/routes/cards.test.ts
+++ b/src/server/routes/cards.test.ts
@@ -74,8 +74,8 @@ function createMockCard(overrides: Partial<Card> = {}): Card {
 	return {
 		id: "card-uuid-123",
 		deckId: "deck-uuid-123",
-		noteId: null,
-		isReversed: null,
+		noteId: "note-uuid-123",
+		isReversed: false,
 		front: "Question",
 		back: "Answer",
 		state: CardState.New,
@@ -110,7 +110,7 @@ function createMockCardWithNoteData(
 ): CardWithNoteData {
 	return {
 		...createMockCard(overrides),
-		note: overrides.note ?? null,
+		note: overrides.note ?? createMockNote(),
 		fieldValues: overrides.fieldValues ?? [],
 	};
 }
@@ -408,7 +408,6 @@ describe("GET /api/decks/:deckId/cards/:cardId", () => {
 		const mockCardWithNote = createMockCardWithNoteData({
 			id: CARD_ID,
 			deckId: DECK_ID,
-			note: null,
 			fieldValues: [],
 		});
 		vi.mocked(mockDeckRepo.findById).mockResolvedValue(
diff --git a/src/server/routes/study.test.ts b/src/server/routes/study.test.ts
index 41abecd..e2fb457 100644
--- a/src/server/routes/study.test.ts
+++ b/src/server/routes/study.test.ts
@@ -80,8 +80,8 @@ function createMockCard(overrides: Partial<Card> = {}): Card {
 	return {
 		id: "card-uuid-123",
 		deckId: "deck-uuid-123",
-		noteId: null,
-		isReversed: null,
+		noteId: "note-uuid-123",
+		isReversed: false,
 		front: "Question",
 		back: "Answer",
 		state: CardState.New,
@@ -122,7 +122,10 @@ function createMockCardForStudy(
 ): CardForStudy {
 	return {
 		...createMockCard(overrides),
-		noteType: overrides.noteType ?? null,
+		noteType: overrides.noteType ?? {
+			frontTemplate: "{{Front}}",
+			backTemplate: "{{Back}}",
+		},
 		fieldValuesMap: overrides.fieldValuesMap ?? {},
 	};
 }
@@ -187,20 +190,18 @@ describe("GET /api/decks/:deckId/study", () => {
 		);
 	});
 
-	it("returns due cards (legacy cards without note)", async () => {
+	it("returns due cards", async () => {
 		const mockCards = [
 			createMockCardForStudy({
 				id: "card-1",
 				front: "Q1",
 				back: "A1",
-				noteType: null,
 				fieldValuesMap: {},
 			}),
 			createMockCardForStudy({
 				id: "card-2",
 				front: "Q2",
 				back: "A2",
-				noteType: null,
 				fieldValuesMap: {},
 			}),
 		];
@@ -217,7 +218,7 @@ describe("GET /api/decks/:deckId/study", () => {
 		expect(res.status).toBe(200);
 		const body = (await res.json()) as StudyResponse;
 		expect(body.cards).toHaveLength(2);
-		expect(body.cards?.[0]?.noteType).toBeNull();
+		expect(body.cards?.[0]?.noteType).toBeDefined();
 	});
 
 	it("returns due cards with note type and field values when available", async () => {
diff --git a/src/server/routes/sync.test.ts b/src/server/routes/sync.test.ts
index 1107acd..f340af7 100644
--- a/src/server/routes/sync.test.ts
+++ b/src/server/routes/sync.test.ts
@@ -186,8 +186,8 @@ describe("POST /api/sync/push", () => {
 		const cardData = {
 			id: "550e8400-e29b-41d4-a716-446655440001",
 			deckId: "550e8400-e29b-41d4-a716-446655440000",
-			noteId: null,
-			isReversed: null,
+			noteId: "550e8400-e29b-41d4-a716-446655440020",
+			isReversed: false,
 			front: "Question",
 			back: "Answer",
 			state: 0,
@@ -435,8 +435,8 @@ describe("POST /api/sync/push", () => {
 		const cardData = {
 			id: "550e8400-e29b-41d4-a716-446655440005",
 			deckId: "550e8400-e29b-41d4-a716-446655440004",
-			noteId: null,
-			isReversed: null,
+			noteId: "550e8400-e29b-41d4-a716-446655440020",
+			isReversed: false,
 			front: "Q",
 			back: "A",
 			state: 0,
@@ -823,8 +823,8 @@ describe("GET /api/sync/pull", () => {
 		const mockCard: Card = {
 			id: "550e8400-e29b-41d4-a716-446655440001",
 			deckId: "550e8400-e29b-41d4-a716-446655440000",
-			noteId: null,
-			isReversed: null,
+			noteId: "550e8400-e29b-41d4-a716-446655440020",
+			isReversed: false,
 			front: "Question",
 			back: "Answer",
 			state: 2,
@@ -928,8 +928,8 @@ describe("GET /api/sync/pull", () => {
 		const mockCard: Card = {
 			id: "550e8400-e29b-41d4-a716-446655440001",
 			deckId: "550e8400-e29b-41d4-a716-446655440000",
-			noteId: null,
-			isReversed: null,
+			noteId: "550e8400-e29b-41d4-a716-446655440020",
+			isReversed: false,
 			front: "Q",
 			back: "A",
 			state: 0,
diff --git a/src/server/routes/sync.ts b/src/server/routes/sync.ts
index f05a7ba..fca099b 100644
--- a/src/server/routes/sync.ts
+++ b/src/server/routes/sync.ts
@@ -26,8 +26,8 @@ const syncDeckSchema = z.object({
 const syncCardSchema = z.object({
 	id: z.uuid(),
 	deckId: z.uuid(),
-	noteId: z.uuid().nullable(),
-	isReversed: z.boolean().nullable(),
+	noteId: z.uuid(),
+	isReversed: z.boolean(),
 	front: z.string().min(1),
 	back: z.string().min(1),
 	state: z.number().int().min(0).max(3),