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

3 files changed, 9 insertions, 6 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
diff --git a/src/client/pages/DeckDetailPage.tsx b/src/client/pages/DeckDetailPage.tsx
index be4dc90..97f8378 100644
--- a/src/client/pages/DeckDetailPage.tsx
+++ b/src/client/pages/DeckDetailPage.tsx
@@ -7,6 +7,7 @@ import { FontAwesomeIcon } from "@fortawesome/react-fontawesome";
 import { useAtomValue } from "jotai";
 import { Suspense } from "react";
 import { Link, useParams } from "wouter";
+import { getEndOfStudyDayBoundary } from "../../shared/date";
 import { cardsByDeckAtomFamily, deckByIdAtomFamily } from "../atoms";
 import { ErrorBoundary } from "../components/ErrorBoundary";
 import { LoadingSpinner } from "../components/LoadingSpinner";
@@ -27,9 +28,9 @@ function DeckHeader({ deckId }: { deckId: string }) {
 function DeckStats({ deckId }: { deckId: string }) {
 	const { data: cards } = useAtomValue(cardsByDeckAtomFamily(deckId));
 
-	// Count cards due today
-	const now = new Date();
-	const dueCards = cards.filter((card) => new Date(card.due) <= now);
+	// Count cards due today (study day boundary is 3:00 AM)
+	const boundary = getEndOfStudyDayBoundary();
+	const dueCards = cards.filter((card) => new Date(card.due) < boundary);
 
 	return (
 		<div className="bg-white rounded-xl border border-border/50 p-6 mb-6">