fix(study): use date-based comparison with 3 AM boundary for due cards

Instead of comparing due timestamps exactly (card.due <= now), compare
against the next 3 AM boundary so all cards due within the current
study day appear at once. This prevents new cards from trickling in
throughout the day when FSRS fuzz spreads due times.

https://claude.ai/code/session_01FeDztLcyGofd6nxh8ct7a3

2 files changed, 5 insertions, 3 deletions

diff --git a/src/client/db/repositories.test.ts b/src/client/db/repositories.test.ts
index 448cb9e..38cf3fb 100644
--- a/src/client/db/repositories.test.ts
+++ b/src/client/db/repositories.test.ts
@@ -299,7 +299,8 @@ describe("localCardRepository", () => {
 	describe("findDueCards", () => {
 		it("should return cards that are due", async () => {
 			const pastDue = new Date(Date.now() - 60000);
-			const future = new Date(Date.now() + 60000);
+			// Use a date far enough in the future to be beyond the next 3 AM boundary
+			const future = new Date(Date.now() + 2 * 24 * 60 * 60 * 1000);
 
 			const card1 = await localCardRepository.create({
 				deckId,
diff --git a/src/client/db/repositories.ts b/src/client/db/repositories.ts
index e01254e..5121bae 100644
--- a/src/client/db/repositories.ts
+++ b/src/client/db/repositories.ts
@@ -1,4 +1,5 @@
 import { v4 as uuidv4 } from "uuid";
+import { getEndOfStudyDayBoundary } from "../../shared/date";
 import {
 	CardState,
 	db,
@@ -140,11 +141,11 @@ export const localCardRepository = {
 	 * Get due cards for a deck
 	 */
 	async findDueCards(deckId: string, limit?: number): Promise<LocalCard[]> {
-		const now = new Date();
+		const boundary = getEndOfStudyDayBoundary();
 		const query = db.cards
 			.where("deckId")
 			.equals(deckId)
-			.filter((card) => card.deletedAt === null && card.due <= now);
+			.filter((card) => card.deletedAt === null && card.due < boundary);
 
 		const cards = await query.toArray();
 		// Sort by due date ascending