feat(debug): add dry-run mutations mode

New 'Dry-run mutations' toggle in the Debug settings panel blocks
outgoing list updates (the + button) and skips the post-mutation
refresh so optimistic UI changes persist locally for testing. The
mutation gate sits in incrementMediaProgress; CleanAnimeList only
revalidates when the request actually went out.

7 files changed, 45 insertions, 6 deletions

diff --git a/src/lib/List/Anime/CleanAnimeList.svelte b/src/lib/List/Anime/CleanAnimeList.svelte
index 3f397c25..42f4d933 100644
--- a/src/lib/List/Anime/CleanAnimeList.svelte
+++ b/src/lib/List/Anime/CleanAnimeList.svelte
@@ -224,10 +224,16 @@ const increment = (anime: Media, progress: number) => {
 			? media.filter((m) => m.id !== anime.id)
 			: media;
 
-	incrementMediaProgress(anime.id, anime.mediaListEntry?.progress, user, () => {
-		pendingUpdate = null;
-		$revalidateAnime = $revalidateAnime + 1;
-	});
+	incrementMediaProgress(
+		anime.id,
+		anime.mediaListEntry?.progress,
+		user,
+		(skipped) => {
+			pendingUpdate = null;
+
+			if (!skipped) $revalidateAnime = $revalidateAnime + 1;
+		},
+	);
 };
 </script>
 
diff --git a/src/lib/Locale/english.ts b/src/lib/Locale/english.ts
index 0cfc4035..f0195948 100644
--- a/src/lib/Locale/english.ts
+++ b/src/lib/Locale/english.ts
@@ -284,6 +284,10 @@ const English: Locale = {
 				"If you are having issues with data loading or logging out, it is recommended to clear your site data.",
 		},
 		dummyLists: "Use dummy media lists",
+		dryRunMutations: {
+			title: "Dry-run mutations",
+			hint: "Block outgoing list updates (e.g., the + button) and skip the post-mutation refresh so optimistic UI changes persist locally for testing. No data is sent to AniList.",
+		},
 	},
 	hololive: {
 		live: "LIVE",
diff --git a/src/lib/Locale/japanese.ts b/src/lib/Locale/japanese.ts
index af309a25..8e3744d4 100644
--- a/src/lib/Locale/japanese.ts
+++ b/src/lib/Locale/japanese.ts
@@ -284,6 +284,10 @@ const Japanese: Locale = {
 				"データの読み込みやログアウトに問題がある場合、サイトデータをクリアすることをお勧めします。",
 		},
 		dummyLists: "ダミーメディアリストを使用する",
+		dryRunMutations: {
+			title: "ドライランモード",
+			hint: "リストの更新リクエスト（＋ボタンなど）の送信をブロックし、更新後の再取得もスキップします。楽観的UIの変更をローカルで保持してテストできます。AniListにはデータは送信されません。",
+		},
 	},
 	hololive: {
 		live: "ライブ",
diff --git a/src/lib/Locale/layout.ts b/src/lib/Locale/layout.ts
index f317ab7f..697404f2 100644
--- a/src/lib/Locale/layout.ts
+++ b/src/lib/Locale/layout.ts
@@ -282,6 +282,10 @@ export interface Locale {
 			hint2: LocaleValue;
 		};
 		dummyLists: LocaleValue;
+		dryRunMutations: {
+			title: LocaleValue;
+			hint: LocaleValue;
+		};
 	};
 	hololive: {
 		live: LocaleValue;
diff --git a/src/lib/Media/Anime/cache.ts b/src/lib/Media/Anime/cache.ts
index e988f255..e1a711ca 100644
--- a/src/lib/Media/Anime/cache.ts
+++ b/src/lib/Media/Anime/cache.ts
@@ -2,6 +2,7 @@ import { get } from "svelte/store";
 import anime from "$stores/anime";
 import { mediaListCollection, Type } from "../../Data/AniList/media";
 import lastPruneTimes from "$stores/lastPruneTimes";
+import settings from "$stores/settings";
 import type {
 	AniListAuthorisation,
 	UserIdentity,
@@ -26,8 +27,19 @@ export const incrementMediaProgress = (
 	id: number,
 	progress: number | undefined,
 	user: AniListAuthorisation,
-	callback: () => void,
+	callback: (skipped?: boolean) => void,
 ) => {
+	if (get(settings).debugDryRunMutations) {
+		console.log(
+			`[dry-run] SaveMediaListEntry(mediaId: ${id}, progress: ${
+				(progress || 0) + 1
+			}) skipped`,
+		);
+		callback(true);
+
+		return;
+	}
+
 	fetch("https://graphql.anilist.co", {
 		method: "POST",
 		headers: {
@@ -40,5 +52,5 @@ export const incrementMediaProgress = (
 				(progress || 0) + 1
 			}) { id } }`,
 		}),
-	}).then(callback);
+	}).then(() => callback(false));
 };
diff --git a/src/lib/Settings/Categories/Debug.svelte b/src/lib/Settings/Categories/Debug.svelte
index ad388fee..6da4b6ae 100644
--- a/src/lib/Settings/Categories/Debug.svelte
+++ b/src/lib/Settings/Categories/Debug.svelte
@@ -15,6 +15,13 @@ import { invalidateListCaches } from "$lib/Media/invalidate";
   setting="debugShowListTimings"
   text={$locale().debug.showListTimings}
 />
+<SettingCheckboxToggle
+  setting="debugDryRunMutations"
+  text={$locale().debug.dryRunMutations.title}
+/>
+<SettingHint lineBreak>
+  {$locale().debug.dryRunMutations.hint}
+</SettingHint>
 <br />
 
 <button onclick={invalidateListCaches}>{$locale().debug.clearCaches}</button>
diff --git a/src/stores/settings.ts b/src/stores/settings.ts
index 24d9eef0..1d808a82 100644
--- a/src/stores/settings.ts
+++ b/src/stores/settings.ts
@@ -71,6 +71,7 @@ export interface Settings {
 	displayDataSaver: boolean;
 	debugDummyLists: boolean;
 	debugShowListTimings: boolean;
+	debugDryRunMutations: boolean;
 	displayScheduleFilterList: boolean;
 	displayReverseSort: boolean;
 	displayAnimeSort: "difference" | "start_date" | "end_date" | "time_remaining";
@@ -128,6 +129,7 @@ const defaultSettings: Settings = {
 	// Debug
 	debugDummyLists: false,
 	debugShowListTimings: false,
+	debugDryRunMutations: false,
 
 	// Calculation
 	calculateChaptersRoundedDown: true,