diff --git a/src/lib/client/cache/thumbnailCache.svelte.ts b/src/lib/client/cache/thumbnailCache.svelte.ts
index fc68558..5a36e3d 100644
--- a/src/lib/client/cache/thumbnailCache.svelte.ts
+++ b/src/lib/client/cache/thumbnailCache.svelte.ts
@@ -1,6 +1,7 @@
+/* eslint-disable svelte/prefer-svelte-reactivity -- Lookup tables of reactive entries */
 import { LRUCache } from "lru-cache";
 import { deleteDirectory, deleteFile, readFile, writeFile } from "#lib/client/storage/opfs.js";
-import type { SummarizedFileInfo } from "#lib/modules/filesystem/index.js";
+import type { SummarizedFileInfo } from "#lib/features/filesystem/index.js";
 import { decryptChunk, encodeToBase64 } from "#lib/shared/crypto/index.js";
 
 export interface Thumbnail {
diff --git a/src/lib/client/keys/sync.ts b/src/lib/client/keys/sync.ts
index dfb68d4..c16c14c 100644
--- a/src/lib/client/keys/sync.ts
+++ b/src/lib/client/keys/sync.ts
@@ -63,8 +63,8 @@ export const requestClientRegistration = async () => {
       answerSig: await answerChallenge(challenge, clientKeys),
     });
     return true;
-  } catch {
-    // TODO: Error Handling
+  } catch (e) {
+    console.error(e);
     return false;
   }
 };
@@ -95,9 +95,9 @@ export const registerInitialMasterKeyAndHmacSecret = async (
     });
   } catch (e) {
     if (isTRPCClientError(e) && (e.data?.code === "FORBIDDEN" || e.data?.code === "CONFLICT")) {
-      return true;
+      return true; // Already registered by another client
     }
-    // TODO: Error Handling
+    console.error(e);
     return false;
   }
 
@@ -107,8 +107,8 @@ export const registerInitialMasterKeyAndHmacSecret = async (
       hsk: hmacSecretWrapped,
     });
     return true;
-  } catch {
-    // TODO: Error Handling
+  } catch (e) {
+    console.error(e);
     return false;
   }
 };
@@ -117,8 +117,8 @@ export const downloadHmacSecrets = async () => {
   let hmacSecretsWrapped;
   try {
     hmacSecretsWrapped = await trpc.hsk.list.query();
-  } catch {
-    // TODO: Error Handling
+  } catch (e) {
+    console.error(e);
     return false;
   }
 
@@ -143,8 +143,8 @@ export const downloadMasterKeys = async () => {
   let masterKeysWrapped;
   try {
     masterKeysWrapped = await trpc.mek.list.query();
-  } catch {
-    // TODO: Error Handling
+  } catch (e) {
+    console.error(e);
     return false;
   }
 
diff --git a/src/lib/client/toast.svelte.ts b/src/lib/client/toast.svelte.ts
new file mode 100644
index 0000000..0b147ce
--- /dev/null
+++ b/src/lib/client/toast.svelte.ts
@@ -0,0 +1,49 @@
+import { isTRPCClientError } from "#trpc/client.js";
+
+export interface Toast {
+  id: number;
+  message: string;
+}
+
+const TOAST_DURATION = 3000;
+
+let toasts: Toast[] = $state([]);
+let nextId = 0;
+
+export const getToasts = () => toasts;
+
+export const showToast = (message: string) => {
+  const toast = { id: nextId++, message };
+  toasts.push(toast);
+  setTimeout(() => {
+    toasts = toasts.filter(({ id }) => id !== toast.id);
+  }, TOAST_DURATION);
+};
+
+const getErrorMessage = (e: unknown, fallbackMessage: string) => {
+  if (isTRPCClientError(e)) {
+    switch (e.data?.code) {
+      case "NOT_FOUND":
+        return "대상을 찾을 수 없어요. 이미 삭제되었을 수 있어요.";
+      case undefined:
+        return "서버에 연결할 수 없어요.";
+    }
+  }
+  return fallbackMessage;
+};
+
+export const showErrorToast = (e: unknown, fallbackMessage: string) => {
+  console.error(e);
+  showToast(getErrorMessage(e, fallbackMessage));
+};
+
+// Runs the action and shows the error to the user if it fails. Returns whether it succeeded.
+export const tryAction = async (action: () => Promise<unknown>, errorMessage: string) => {
+  try {
+    await action();
+    return true;
+  } catch (e) {
+    showErrorToast(e, errorMessage);
+    return false;
+  }
+};
diff --git a/src/lib/components/atoms/Toasts.svelte b/src/lib/components/atoms/Toasts.svelte
new file mode 100644
index 0000000..66c28a4
--- /dev/null
+++ b/src/lib/components/atoms/Toasts.svelte
@@ -0,0 +1,16 @@
+<script lang="ts">
+  import { fly } from "svelte/transition";
+  import { getToasts } from "#lib/client/toast.svelte.js";
+</script>
+
+<div class="pointer-events-none fixed inset-x-0 top-4 z-50 flex flex-col items-center gap-y-2 px-4">
+  {#each getToasts() as toast (toast.id)}
+    <div
+      role="alert"
+      transition:fly={{ y: -8, duration: 200 }}
+      class="max-w-md rounded-xl bg-gray-800 px-4 py-3 text-sm break-keep text-white shadow-lg"
+    >
+      {toast.message}
+    </div>
+  {/each}
+</div>
diff --git a/src/lib/components/atoms/buttons/FileThumbnailButton.svelte b/src/lib/components/atoms/buttons/FileThumbnailButton.svelte
index b8dfdb1..098be9b 100644
--- a/src/lib/components/atoms/buttons/FileThumbnailButton.svelte
+++ b/src/lib/components/atoms/buttons/FileThumbnailButton.svelte
@@ -1,6 +1,6 @@
 <script lang="ts">
   import { getFileThumbnail } from "#lib/client/cache/index.js";
-  import type { SummarizedFileInfo } from "#lib/modules/filesystem/index.js";
+  import type { SummarizedFileInfo } from "#lib/features/filesystem/index.js";
 
   import IconFavorite from "~icons/material-symbols/favorite";
 
diff --git a/src/lib/components/atoms/index.ts b/src/lib/components/atoms/index.ts
index 5ab8892..1ba53f7 100644
--- a/src/lib/components/atoms/index.ts
+++ b/src/lib/components/atoms/index.ts
@@ -5,3 +5,4 @@ export * from "./divs";
 export * from "./inputs";
 export { default as Modal } from "./Modal.svelte";
 export { default as RowVirtualizer } from "./RowVirtualizer.svelte";
+export { default as Toasts } from "./Toasts.svelte";
diff --git a/src/lib/components/molecules/Categories.svelte b/src/lib/components/molecules/Categories.svelte
index feceedb..1aa791c 100644
--- a/src/lib/components/molecules/Categories.svelte
+++ b/src/lib/components/molecules/Categories.svelte
@@ -1,5 +1,5 @@
 <script module lang="ts">
-  import type { DataKey } from "#lib/modules/filesystem/index.js";
+  import type { DataKey } from "#lib/features/filesystem/index.js";
 
   export interface SelectedCategory {
     id: number;
@@ -13,7 +13,7 @@
   import type { SvelteHTMLElements } from "svelte/elements";
   import { ActionEntryButton } from "#lib/components/atoms/index.js";
   import { CategoryLabel } from "#lib/components/molecules/index.js";
-  import type { SubCategoryInfo } from "#lib/modules/filesystem/index.js";
+  import type { SubCategoryInfo } from "#lib/features/filesystem/index.js";
   import { sortEntries } from "#lib/utils/index.js";
 
   interface Props {
diff --git a/src/lib/components/molecules/SubCategories.svelte b/src/lib/components/molecules/SubCategories.svelte
index 1248b17..820f960 100644
--- a/src/lib/components/molecules/SubCategories.svelte
+++ b/src/lib/components/molecules/SubCategories.svelte
@@ -6,7 +6,7 @@
     IconEntryButton,
     type SelectedCategory,
   } from "#lib/components/molecules/index.js";
-  import type { CategoryInfo } from "#lib/modules/filesystem/index.js";
+  import type { CategoryInfo } from "#lib/features/filesystem/index.js";
 
   import IconAddCircle from "~icons/material-symbols/add-circle";
 
diff --git a/src/lib/features/auth/index.ts b/src/lib/features/auth/index.ts
new file mode 100644
index 0000000..1b0f9be
--- /dev/null
+++ b/src/lib/features/auth/index.ts
@@ -0,0 +1,13 @@
+import { trpc } from "#trpc/client.js";
+
+export const login = async (email: string, password: string) => {
+  await trpc.auth.login.mutate({ email, password });
+};
+
+export const logout = async () => {
+  await trpc.auth.logout.mutate();
+};
+
+export const changePassword = async (oldPassword: string, newPassword: string) => {
+  await trpc.auth.changePassword.mutate({ oldPassword, newPassword });
+};
diff --git a/src/lib/features/favorites/index.ts b/src/lib/features/favorites/index.ts
new file mode 100644
index 0000000..893085d
--- /dev/null
+++ b/src/lib/features/favorites/index.ts
@@ -0,0 +1,54 @@
+import {
+  getDirectoryInfo,
+  getFileInfo,
+  setDirectoryFavorite,
+  setFileFavorite,
+  type LocalDirectoryInfo,
+  type SummarizedFileInfo,
+} from "#lib/features/filesystem/index.js";
+import { sortEntries } from "#lib/utils/index.js";
+import { trpc } from "#trpc/client.js";
+
+export type FavoriteEntry =
+  | { type: "directory"; name: string; details: LocalDirectoryInfo }
+  | { type: "file"; name: string; details: SummarizedFileInfo };
+
+export const getFavoriteEntries = async () => {
+  const favorites = await trpc.favorites.get.query();
+  const [directories, files] = await Promise.all([
+    Promise.all(
+      favorites.directories.map((directory) =>
+        getDirectoryInfo(directory.id, { serverResponse: { ...directory, isFavorite: true } }),
+      ),
+    ),
+    Promise.all(
+      favorites.files.map((file) =>
+        getFileInfo(file.id, { serverResponse: { ...file, isFavorite: true } }),
+      ),
+    ),
+  ]);
+  return [
+    ...sortEntries(
+      directories.map((directory): FavoriteEntry => ({
+        type: "directory",
+        name: directory.name!,
+        details: directory as LocalDirectoryInfo,
+      })),
+    ),
+    ...sortEntries(
+      files.map((file): FavoriteEntry => ({
+        type: "file",
+        name: file.name!,
+        details: file as SummarizedFileInfo,
+      })),
+    ),
+  ];
+};
+
+export const removeFavorite = async ({ type, details }: FavoriteEntry) => {
+  if (type === "directory") {
+    await setDirectoryFavorite(details, false);
+  } else {
+    await setFileFavorite(details, false);
+  }
+};
diff --git a/src/lib/features/filesystem/cache.svelte.ts b/src/lib/features/filesystem/cache.svelte.ts
new file mode 100644
index 0000000..bb2585d
--- /dev/null
+++ b/src/lib/features/filesystem/cache.svelte.ts
@@ -0,0 +1,139 @@
+/* eslint-disable svelte/prefer-svelte-reactivity -- Lookup tables of reactive entries */
+import { untrack } from "svelte";
+
+interface FilesystemCacheOptions<K, V> {
+  fetchFromIndexedDB: (key: K) => Promise<V | undefined>;
+  fetchFromServer: (key: K, cachedValue: V | undefined) => Promise<V>;
+  bulkFetchFromIndexedDB?: (keys: Set<K>) => Promise<Map<K, V>>;
+  bulkFetchFromServer?: (keys: Map<K, { cachedValue: V | undefined }>) => Promise<Map<K, V>>;
+}
+
+interface Entry<V> {
+  value?: V;
+  promise?: Promise<V>;
+}
+
+// Caches filesystem entries as reactive objects which are updated in place, so that every view
+// of an entry reflects its latest state. Values are first loaded from IndexedDB (if any) and then
+// revalidated against the server.
+export class FilesystemCache<K, V extends object> {
+  private map = new Map<K, Entry<V>>();
+
+  constructor(private readonly options: FilesystemCacheOptions<K, V>) {}
+
+  private getOrCreateEntry(key: K) {
+    let entry = this.map.get(key);
+    if (!entry) {
+      const newEntry: Entry<V> = $state({});
+      entry = newEntry;
+      this.map.set(key, entry);
+    }
+    return entry;
+  }
+
+  private settle(entry: Entry<V>, value: V) {
+    if (entry.value) {
+      Object.assign(entry.value, value);
+    } else {
+      entry.value = value;
+    }
+    return entry.value!;
+  }
+
+  // Returns the cached value synchronously if available, and revalidates it in the background
+  get(key: K, options?: { fetchFromServer?: (cachedValue: V | undefined) => Promise<V> }) {
+    return untrack(() => {
+      const entry = this.getOrCreateEntry(key);
+      if (entry.promise) return entry.value ?? entry.promise;
+
+      const { promise, resolve, reject } = Promise.withResolvers<V>();
+      promise.catch(() => {}); // Rejections are handled by callers waiting for the promise
+      entry.promise = promise;
+
+      (async () => {
+        let cachedValue = entry.value && ($state.snapshot(entry.value) as V);
+        if (!cachedValue) {
+          cachedValue = await this.options.fetchFromIndexedDB(key);
+          if (cachedValue) {
+            resolve(this.settle(entry, cachedValue));
+          }
+        }
+
+        const loadedValue = await (options?.fetchFromServer?.(cachedValue) ??
+          this.options.fetchFromServer(key, cachedValue));
+        resolve(this.settle(entry, loadedValue));
+      })()
+        .catch((e) => {
+          console.error(e);
+          reject(e);
+        })
+        .finally(() => {
+          entry.promise = undefined;
+        });
+
+      return entry.value ?? promise;
+    });
+  }
+
+  bulkGet(keys: Set<K>) {
+    return untrack(() => {
+      const pending = new Map<K, PromiseWithResolvers<V>>();
+      for (const key of keys) {
+        const entry = this.getOrCreateEntry(key);
+        if (entry.promise) continue;
+
+        const resolvers = Promise.withResolvers<V>();
+        resolvers.promise.catch(() => {});
+        entry.promise = resolvers.promise;
+        pending.set(key, resolvers);
+      }
+
+      const settleAll = (values: Map<K, V>) => {
+        values.forEach((value, key) => {
+          pending.get(key)?.resolve(this.settle(this.map.get(key)!, value));
+        });
+      };
+
+      (async () => {
+        const pendingKeys = [...pending.keys()];
+        settleAll(
+          await this.options.bulkFetchFromIndexedDB!(
+            new Set(pendingKeys.filter((key) => !this.map.get(key)!.value)),
+          ),
+        );
+        settleAll(
+          await this.options.bulkFetchFromServer!(
+            new Map(pendingKeys.map((key) => [key, { cachedValue: this.map.get(key)!.value }])),
+          ),
+        );
+      })()
+        .catch((e) => {
+          console.error(e);
+          pending.forEach(({ reject }) => reject(e));
+        })
+        .finally(() => {
+          pending.forEach((_, key) => {
+            this.map.get(key)!.promise = undefined;
+          });
+        });
+
+      const makeResult = () => new Map([...keys].map((key) => [key, this.map.get(key)!.value!]));
+      const waiting = [...keys]
+        .map((key) => this.map.get(key)!)
+        .filter((entry) => !entry.value)
+        .map((entry) => entry.promise!);
+      return waiting.length > 0 ? Promise.all(waiting).then(makeResult) : makeResult();
+    });
+  }
+
+  // Revalidates the entry if it has been loaded
+  invalidate(key: K) {
+    if (this.map.has(key)) {
+      void Promise.resolve(this.get(key)).catch(() => {});
+    }
+  }
+
+  evict(key: K) {
+    this.map.delete(key);
+  }
+}
diff --git a/src/lib/modules/filesystem/category.ts b/src/lib/features/filesystem/category.ts
similarity index 61%
rename from src/lib/modules/filesystem/category.ts
rename to src/lib/features/filesystem/category.ts
index 3d1afac..25db60e 100644
--- a/src/lib/modules/filesystem/category.ts
+++ b/src/lib/features/filesystem/category.ts
@@ -1,7 +1,15 @@
 import * as IndexedDB from "#lib/client/storage/indexedDB/index.js";
-import { trpc, isTRPCClientError } from "#trpc/client.js";
-import { FilesystemCache, decryptFileMetadata, decryptCategoryMetadata } from "./internal.svelte";
-import type { CategoryInfo, MaybeCategoryInfo } from "./types";
+import { isTRPCClientError, trpc } from "#trpc/client.js";
+import { FilesystemCache } from "./cache.svelte";
+import { invalidateFile } from "./file";
+import {
+  decryptCategoryMetadata,
+  decryptFileMetadata,
+  encryptName,
+  generateEntryKeys,
+} from "./metadata";
+import { useResource } from "./resource.svelte";
+import type { CategoryInfo, DataKey, LocalCategoryInfo, MaybeCategoryInfo } from "./types";
 
 const cache = new FilesystemCache<CategoryId, MaybeCategoryInfo>({
   async fetchFromIndexedDB(id) {
@@ -121,3 +129,57 @@ const storeToIndexedDB = (info: CategoryInfo) => {
 export const getCategoryInfo = (id: CategoryId) => {
   return cache.get(id);
 };
+
+export const useCategory = (getId: () => CategoryId) => {
+  return useResource(getId, (id) => getCategoryInfo(id));
+};
+
+export const invalidateCategory = (id: CategoryId) => {
+  cache.invalidate(id);
+};
+
+export const createCategory = async (parentId: CategoryId, name: string) => {
+  await trpc.category.create.mutate({ parent: parentId, ...(await generateEntryKeys(name)) });
+  invalidateCategory(parentId);
+};
+
+export const renameCategory = async (
+  category: { id: number; parentId: CategoryId; dataKey?: DataKey },
+  newName: string,
+) => {
+  if (!category.dataKey) {
+    throw new Error("Data key not loaded");
+  }
+
+  await trpc.category.rename.mutate({
+    id: category.id,
+    dekVersion: category.dataKey.version,
+    ...(await encryptName(newName, category.dataKey.key)),
+  });
+  invalidateCategory(category.parentId);
+  invalidateCategory(category.id);
+};
+
+export const deleteCategory = async (category: { id: number; parentId: CategoryId }) => {
+  await trpc.category.delete.mutate({ id: category.id });
+  cache.evict(category.id);
+  invalidateCategory(category.parentId);
+};
+
+export const addFileToCategory = async (fileId: number, categoryId: number) => {
+  await trpc.category.addFile.mutate({ id: categoryId, file: fileId });
+  invalidateFile(fileId);
+  invalidateCategory(categoryId);
+};
+
+export const removeFileFromCategory = async (fileId: number, categoryId: number) => {
+  await trpc.category.removeFile.mutate({ id: categoryId, file: fileId });
+  invalidateFile(fileId);
+  invalidateCategory(categoryId);
+};
+
+// Whether to show the files of subcategories is a local preference
+export const setCategoryFileRecursive = async (category: LocalCategoryInfo, value: boolean) => {
+  category.isFileRecursive = value;
+  await IndexedDB.updateCategoryInfo(category.id, { isFileRecursive: value });
+};
diff --git a/src/lib/features/filesystem/content.ts b/src/lib/features/filesystem/content.ts
new file mode 100644
index 0000000..decc283
--- /dev/null
+++ b/src/lib/features/filesystem/content.ts
@@ -0,0 +1,62 @@
+import {
+  deleteFileCache,
+  deleteFileThumbnailCache,
+  getFileCache,
+  storeFileCache,
+  storeFileThumbnailCache,
+} from "#lib/client/cache/index.js";
+import { getDecryptedFileUrl, prepareFileDecryption } from "#lib/client/serviceWorker.js";
+import { getAllFileInfos } from "#lib/client/storage/indexedDB/index.js";
+import { uploadBlob } from "#lib/client/transfer/chunkedUpload.js";
+import { downloadFile } from "#lib/client/transfer/index.js";
+import { trpc } from "#trpc/client.js";
+import type { DataKey } from "./types";
+
+// Returns the decrypted content of the file, from the cache if available
+export const getFileContent = async (fileId: number, dataKey: CryptoKey, isLegacy: boolean) => {
+  const cache = await getFileCache(fileId);
+  if (cache) return cache;
+
+  const fileBuffer = await downloadFile(fileId, dataKey, isLegacy);
+  void storeFileCache(fileId, fileBuffer);
+  return fileBuffer;
+};
+
+// Returns a URL from which the service worker streams the decrypted file
+export const getFileStreamUrl = async (fileId: number, dataKey: CryptoKey, contentType: string) => {
+  const res = await fetch(`/api/file/${fileId}/download`, { method: "HEAD" });
+  if (!res.ok) {
+    throw new Error("Failed to get the file size");
+  }
+
+  const encContentSize = parseInt(res.headers.get("Content-Length") ?? "0", 10);
+  if (encContentSize <= 0) {
+    throw new Error("Invalid file size");
+  }
+
+  await prepareFileDecryption(fileId, { isLegacy: false, dataKey, encContentSize, contentType });
+  return getDecryptedFileUrl(fileId);
+};
+
+export const uploadFileThumbnail = async (fileId: number, thumbnail: Blob, dataKey: DataKey) => {
+  const { uploadId } = await trpc.upload.startFileThumbnailUpload.mutate({
+    file: fileId,
+    dekVersion: dataKey.version,
+  });
+  await uploadBlob(uploadId, thumbnail, dataKey.key);
+  await trpc.upload.completeFileThumbnailUpload.mutate({ uploadId });
+
+  await storeFileThumbnailCache(fileId, await thumbnail.arrayBuffer());
+};
+
+// Deletes local caches of files deleted on other devices
+export const cleanupDeletedFileCaches = async () => {
+  const liveFiles = new Set(await trpc.file.list.query());
+  const maybeCachedFiles = await getAllFileInfos();
+
+  await Promise.all(
+    maybeCachedFiles
+      .filter(({ id }) => !liveFiles.has(id))
+      .flatMap(({ id }) => [deleteFileCache(id), deleteFileThumbnailCache(id)]),
+  );
+};
diff --git a/src/lib/modules/filesystem/directory.ts b/src/lib/features/filesystem/directory.ts
similarity index 62%
rename from src/lib/modules/filesystem/directory.ts
rename to src/lib/features/filesystem/directory.ts
index 47e2979..9027743 100644
--- a/src/lib/modules/filesystem/directory.ts
+++ b/src/lib/features/filesystem/directory.ts
@@ -1,7 +1,15 @@
+import { deleteFileCache, deleteFileThumbnailCache } from "#lib/client/cache/index.js";
 import * as IndexedDB from "#lib/client/storage/indexedDB/index.js";
-import { trpc, isTRPCClientError } from "#trpc/client.js";
-import { FilesystemCache, decryptDirectoryMetadata, decryptFileMetadata } from "./internal.svelte";
-import type { DirectoryInfo, MaybeDirectoryInfo } from "./types";
+import { isTRPCClientError, trpc } from "#trpc/client.js";
+import { FilesystemCache } from "./cache.svelte";
+import {
+  decryptDirectoryMetadata,
+  decryptFileMetadata,
+  encryptName,
+  generateEntryKeys,
+} from "./metadata";
+import { useResource } from "./resource.svelte";
+import type { DataKey, DirectoryInfo, MaybeDirectoryInfo } from "./types";
 
 const cache = new FilesystemCache<DirectoryId, MaybeDirectoryInfo>({
   async fetchFromIndexedDB(id) {
@@ -31,7 +39,7 @@ const cache = new FilesystemCache<DirectoryId, MaybeDirectoryInfo>({
     }
   },
 
-  async fetchFromServer(id, _cachedInfo) {
+  async fetchFromServer(id) {
     try {
       const directory = await trpc.directory.get.query({ id });
       const [subDirectories, files, metadata] = await Promise.all([
@@ -132,3 +140,56 @@ export const getDirectoryInfo = (
       }),
   });
 };
+
+export const useDirectory = (getId: () => DirectoryId) => {
+  return useResource(getId, (id) => getDirectoryInfo(id));
+};
+
+export const invalidateDirectory = (id: DirectoryId) => {
+  cache.invalidate(id);
+};
+
+export const createDirectory = async (parentId: DirectoryId, name: string) => {
+  await trpc.directory.create.mutate({ parent: parentId, ...(await generateEntryKeys(name)) });
+  invalidateDirectory(parentId);
+};
+
+export const renameDirectory = async (
+  directory: { id: number; parentId: DirectoryId; dataKey?: DataKey },
+  newName: string,
+) => {
+  if (!directory.dataKey) {
+    throw new Error("Data key not loaded");
+  }
+
+  await trpc.directory.rename.mutate({
+    id: directory.id,
+    dekVersion: directory.dataKey.version,
+    ...(await encryptName(newName, directory.dataKey.key)),
+  });
+  invalidateDirectory(directory.parentId);
+  invalidateDirectory(directory.id);
+};
+
+export const deleteDirectory = async (directory: { id: number; parentId: DirectoryId }) => {
+  const { deletedFiles } = await trpc.directory.delete.mutate({ id: directory.id });
+  cache.evict(directory.id);
+  invalidateDirectory(directory.parentId);
+
+  await Promise.all(
+    deletedFiles.flatMap((fileId) => [deleteFileCache(fileId), deleteFileThumbnailCache(fileId)]),
+  );
+};
+
+export const setDirectoryFavorite = async (
+  directory: { id: number; parentId: DirectoryId },
+  isFavorite: boolean,
+) => {
+  if (isFavorite) {
+    await trpc.favorites.addDirectory.mutate({ id: directory.id });
+  } else {
+    await trpc.favorites.removeDirectory.mutate({ id: directory.id });
+  }
+  invalidateDirectory(directory.parentId);
+  invalidateDirectory(directory.id);
+};
diff --git a/src/lib/modules/filesystem/file.ts b/src/lib/features/filesystem/file.ts
similarity index 77%
rename from src/lib/modules/filesystem/file.ts
rename to src/lib/features/filesystem/file.ts
index 81892ff..5eda130 100644
--- a/src/lib/modules/filesystem/file.ts
+++ b/src/lib/features/filesystem/file.ts
@@ -1,7 +1,11 @@
+import { deleteFileCache, deleteFileThumbnailCache } from "#lib/client/cache/index.js";
 import * as IndexedDB from "#lib/client/storage/indexedDB/index.js";
-import { trpc, isTRPCClientError } from "#trpc/client.js";
-import { FilesystemCache, decryptFileMetadata, decryptCategoryMetadata } from "./internal.svelte";
-import type { FileInfo, MaybeFileInfo } from "./types";
+import { isTRPCClientError, trpc } from "#trpc/client.js";
+import { FilesystemCache } from "./cache.svelte";
+import { invalidateDirectory } from "./directory";
+import { decryptCategoryMetadata, decryptFileMetadata, encryptName } from "./metadata";
+import { useResource } from "./resource.svelte";
+import type { DataKey, FileInfo, MaybeFileInfo } from "./types";
 
 const cache = new FilesystemCache<number, MaybeFileInfo>({
   async fetchFromIndexedDB(id) {
@@ -32,7 +36,7 @@ const cache = new FilesystemCache<number, MaybeFileInfo>({
     }
   },
 
-  async fetchFromServer(id, _cachedInfo) {
+  async fetchFromServer(id) {
     try {
       const file = await trpc.file.get.query({ id });
       const [categories, metadata] = await Promise.all([
@@ -211,3 +215,49 @@ export const getFileInfo = (
 export const bulkGetFileInfo = (ids: number[]) => {
   return cache.bulkGet(new Set(ids));
 };
+
+export const useFile = (getId: () => number) => {
+  return useResource(getId, (id) => getFileInfo(id));
+};
+
+export const invalidateFile = (id: number) => {
+  cache.invalidate(id);
+};
+
+export const renameFile = async (
+  file: { id: number; parentId: DirectoryId; dataKey?: DataKey },
+  newName: string,
+) => {
+  if (!file.dataKey) {
+    throw new Error("Data key not loaded");
+  }
+
+  await trpc.file.rename.mutate({
+    id: file.id,
+    dekVersion: file.dataKey.version,
+    ...(await encryptName(newName, file.dataKey.key)),
+  });
+  invalidateDirectory(file.parentId);
+  invalidateFile(file.id);
+};
+
+export const deleteFile = async (file: { id: number; parentId: DirectoryId }) => {
+  await trpc.file.delete.mutate({ id: file.id });
+  cache.evict(file.id);
+  invalidateDirectory(file.parentId);
+
+  await Promise.all([deleteFileCache(file.id), deleteFileThumbnailCache(file.id)]);
+};
+
+export const setFileFavorite = async (
+  file: { id: number; parentId: DirectoryId },
+  isFavorite: boolean,
+) => {
+  if (isFavorite) {
+    await trpc.favorites.addFile.mutate({ id: file.id });
+  } else {
+    await trpc.favorites.removeFile.mutate({ id: file.id });
+  }
+  invalidateDirectory(file.parentId);
+  invalidateFile(file.id);
+};
diff --git a/src/lib/modules/filesystem/index.ts b/src/lib/features/filesystem/index.ts
similarity index 66%
rename from src/lib/modules/filesystem/index.ts
rename to src/lib/features/filesystem/index.ts
index cb9e0f4..949717f 100644
--- a/src/lib/modules/filesystem/index.ts
+++ b/src/lib/features/filesystem/index.ts
@@ -1,4 +1,6 @@
 export * from "./category";
+export * from "./content";
 export * from "./directory";
 export * from "./file";
 export * from "./types";
+export * from "./upload";
diff --git a/src/lib/features/filesystem/metadata.ts b/src/lib/features/filesystem/metadata.ts
new file mode 100644
index 0000000..1ae3a30
--- /dev/null
+++ b/src/lib/features/filesystem/metadata.ts
@@ -0,0 +1,83 @@
+import { keyring } from "#lib/client/keys/index.js";
+import {
+  decryptString,
+  encryptString,
+  generateDataKey,
+  unwrapDataKey,
+  wrapDataKey,
+} from "#lib/shared/crypto/index.js";
+
+const unwrapEntryDataKey = async (metadata: { mekVersion: number; dek: string }) => {
+  const { dataKey } = await unwrapDataKey(
+    metadata.dek,
+    keyring.getMasterKey(metadata.mekVersion).key,
+  );
+  return dataKey;
+};
+
+export const decryptDirectoryMetadata = async (metadata: {
+  mekVersion: number;
+  dek: string;
+  dekVersion: Date;
+  name: string;
+  nameIv: string;
+}) => {
+  const dataKey = await unwrapEntryDataKey(metadata);
+  const name = await decryptString(metadata.name, metadata.nameIv, dataKey);
+
+  return {
+    dataKey: { key: dataKey, version: metadata.dekVersion },
+    name,
+  };
+};
+
+const decryptDate = async (ciphertext: string, iv: string, dataKey: CryptoKey) => {
+  return new Date(parseInt(await decryptString(ciphertext, iv, dataKey), 10));
+};
+
+export const decryptFileMetadata = async (metadata: {
+  mekVersion: number;
+  dek: string;
+  dekVersion: Date;
+  name: string;
+  nameIv: string;
+  createdAt?: string;
+  createdAtIv?: string;
+  lastModifiedAt: string;
+  lastModifiedAtIv: string;
+}) => {
+  const dataKey = await unwrapEntryDataKey(metadata);
+  const [name, createdAt, lastModifiedAt] = await Promise.all([
+    decryptString(metadata.name, metadata.nameIv, dataKey),
+    metadata.createdAt
+      ? decryptDate(metadata.createdAt, metadata.createdAtIv!, dataKey)
+      : undefined,
+    decryptDate(metadata.lastModifiedAt, metadata.lastModifiedAtIv, dataKey),
+  ]);
+
+  return {
+    dataKey: { key: dataKey, version: metadata.dekVersion },
+    name,
+    createdAt,
+    lastModifiedAt,
+  };
+};
+
+export const decryptCategoryMetadata = decryptDirectoryMetadata;
+
+export const encryptName = async (name: string, dataKey: CryptoKey) => {
+  const { ciphertext, iv } = await encryptString(name, dataKey);
+  return { name: ciphertext, nameIv: iv };
+};
+
+// Generates the keys of a new directory or category encrypted with the active master key
+export const generateEntryKeys = async (name: string) => {
+  const masterKey = keyring.activeMasterKey;
+  const { dataKey, dataKeyVersion } = await generateDataKey();
+  return {
+    mekVersion: masterKey.version,
+    dek: await wrapDataKey(dataKey, masterKey.key),
+    dekVersion: dataKeyVersion,
+    ...(await encryptName(name, dataKey)),
+  };
+};
diff --git a/src/lib/features/filesystem/resource.svelte.ts b/src/lib/features/filesystem/resource.svelte.ts
new file mode 100644
index 0000000..5cefe81
--- /dev/null
+++ b/src/lib/features/filesystem/resource.svelte.ts
@@ -0,0 +1,33 @@
+import { untrack } from "svelte";
+
+// Exposes the value of a cache entry identified by a reactive key. Cached values are available
+// synchronously, so that views don't flicker while revalidating.
+export const useResource = <K, V>(getKey: () => K, load: (key: K) => V | Promise<V>) => {
+  let current: V | undefined = $state();
+
+  $effect.pre(() => {
+    const key = getKey();
+    let isStale = false;
+
+    const result = untrack(() => load(key));
+    if (result instanceof Promise) {
+      result
+        .then((value) => {
+          if (!isStale) current = value;
+        })
+        .catch(() => {}); // Logged by the cache
+    } else {
+      current = result;
+    }
+
+    return () => {
+      isStale = true;
+    };
+  });
+
+  return {
+    get current() {
+      return current;
+    },
+  };
+};
diff --git a/src/lib/modules/filesystem/types.ts b/src/lib/features/filesystem/types.ts
similarity index 98%
rename from src/lib/modules/filesystem/types.ts
rename to src/lib/features/filesystem/types.ts
index 254d4c7..5d2b46f 100644
--- a/src/lib/modules/filesystem/types.ts
+++ b/src/lib/features/filesystem/types.ts
@@ -49,7 +49,7 @@ export type CategoryFileInfo = SummarizedFileInfo & { isRecursive: boolean };
 
 export interface LocalCategoryInfo {
   id: number;
-  parentId: DirectoryId;
+  parentId: CategoryId;
   dataKey?: DataKey;
   name: string;
   subCategories: SubCategoryInfo[];
diff --git a/src/lib/features/filesystem/upload.ts b/src/lib/features/filesystem/upload.ts
new file mode 100644
index 0000000..abfb7b2
--- /dev/null
+++ b/src/lib/features/filesystem/upload.ts
@@ -0,0 +1,22 @@
+import { storeFileCache, storeFileThumbnailCache } from "#lib/client/cache/index.js";
+import { uploadFile as doUploadFile } from "#lib/client/transfer/index.js";
+import { invalidateDirectory } from "./directory";
+
+// Uploads the file and caches it locally. Returns `false` if the upload is canceled.
+export const uploadFile = async (
+  file: File,
+  parentId: DirectoryId,
+  onDuplicate: () => Promise<boolean>,
+) => {
+  const res = await doUploadFile(file, parentId, onDuplicate);
+  if (!res) return false;
+
+  invalidateDirectory(parentId);
+  if (res.fileBuffer) {
+    void storeFileCache(res.fileId, res.fileBuffer);
+  }
+  if (res.thumbnailBuffer) {
+    void storeFileThumbnailCache(res.fileId, res.thumbnailBuffer);
+  }
+  return true;
+};
diff --git a/src/routes/(fullscreen)/search/service.ts b/src/lib/features/search/index.ts
similarity index 56%
rename from src/routes/(fullscreen)/search/service.ts
rename to src/lib/features/search/index.ts
index b714cc8..b87f299 100644
--- a/src/routes/(fullscreen)/search/service.ts
+++ b/src/lib/features/search/index.ts
@@ -1,11 +1,10 @@
 import {
   getDirectoryInfo,
   getFileInfo,
-  type LocalDirectoryInfo,
   type FileInfo,
   type LocalCategoryInfo,
-} from "#lib/modules/filesystem/index.js";
-import { HybridPromise } from "#lib/utils/index.js";
+  type LocalDirectoryInfo,
+} from "#lib/features/filesystem/index.js";
 import { trpc } from "#trpc/client.js";
 
 export interface SearchFilter {
@@ -19,24 +18,24 @@ export interface SearchResult {
   files: FileInfo[];
 }
 
-export const requestSearch = async (filter: SearchFilter) => {
+const getCategoryIds = (filter: SearchFilter, type: "include" | "exclude") => {
+  return filter.categories.filter((category) => category.type === type).map(({ info }) => info.id);
+};
+
+export const search = async (filter: SearchFilter) => {
   const { directories: directoriesRaw, files: filesRaw } = await trpc.search.search.query({
     ancestor: filter.ancestorId,
     inFavorites: filter.inFavorites,
-    includeCategories: filter.categories
-      .filter(({ type }) => type === "include")
-      .map(({ info }) => info.id),
-    excludeCategories: filter.categories
-      .filter(({ type }) => type === "exclude")
-      .map(({ info }) => info.id),
+    includeCategories: getCategoryIds(filter, "include"),
+    excludeCategories: getCategoryIds(filter, "exclude"),
   });
-  const [directories, files] = await HybridPromise.all([
-    HybridPromise.all(
+  const [directories, files] = await Promise.all([
+    Promise.all(
       directoriesRaw.map((directory) =>
         getDirectoryInfo(directory.id, { serverResponse: directory }),
       ),
     ),
-    HybridPromise.all(filesRaw.map((file) => getFileInfo(file.id, { serverResponse: file }))),
+    Promise.all(filesRaw.map((file) => getFileInfo(file.id, { serverResponse: file }))),
   ]);
   return { directories, files } as SearchResult;
 };
diff --git a/src/lib/modules/filesystem/internal.svelte.ts b/src/lib/modules/filesystem/internal.svelte.ts
deleted file mode 100644
index ef96aaf..0000000
--- a/src/lib/modules/filesystem/internal.svelte.ts
+++ /dev/null
@@ -1,181 +0,0 @@
-import { untrack } from "svelte";
-import { keyring } from "#lib/client/keys/index.js";
-import { unwrapDataKey, decryptString } from "#lib/shared/crypto/index.js";
-
-interface FilesystemCacheOptions<K, V> {
-  fetchFromIndexedDB: (key: K) => Promise<V | undefined>;
-  fetchFromServer: (key: K, cachedValue: V | undefined) => Promise<V>;
-  bulkFetchFromIndexedDB?: (keys: Set<K>) => Promise<Map<K, V>>;
-  bulkFetchFromServer?: (keys: Map<K, { cachedValue: V | undefined }>) => Promise<Map<K, V>>;
-}
-
-export class FilesystemCache<K, V extends object> {
-  private map = new Map<K, { value?: V; promise?: Promise<V> }>();
-
-  constructor(private readonly options: FilesystemCacheOptions<K, V>) {}
-
-  get(key: K, options?: { fetchFromServer?: (cachedValue: V | undefined) => Promise<V> }) {
-    return untrack(() => {
-      let state = this.map.get(key);
-      if (state?.promise) return state.value ?? state.promise;
-
-      const { promise: newPromise, resolve } = Promise.withResolvers<V>();
-
-      if (!state) {
-        const newState = $state({});
-        state = newState;
-        this.map.set(key, newState);
-      }
-
-      (state.value
-        ? Promise.resolve($state.snapshot(state.value) as V)
-        : this.options.fetchFromIndexedDB(key).then((loadedInfo) => {
-            if (loadedInfo) {
-              state.value = loadedInfo;
-              resolve(state.value);
-            }
-            return loadedInfo;
-          })
-      )
-        .then(
-          (cachedInfo) =>
-            options?.fetchFromServer?.(cachedInfo) ?? this.options.fetchFromServer(key, cachedInfo),
-        )
-        .then((loadedInfo) => {
-          if (state.value) {
-            Object.assign(state.value, loadedInfo);
-          } else {
-            state.value = loadedInfo;
-          }
-          resolve(state.value);
-        })
-        .finally(() => {
-          state.promise = undefined;
-        });
-
-      state.promise = newPromise;
-      return state.value ?? newPromise;
-    });
-  }
-
-  bulkGet(keys: Set<K>) {
-    return untrack(() => {
-      const newPromises = new Map(
-        keys
-          .keys()
-          .filter((key) => this.map.get(key)?.promise === undefined)
-          .map((key) => [key, Promise.withResolvers<V>()]),
-      );
-      newPromises.forEach(({ promise }, key) => {
-        const state = this.map.get(key);
-        if (state) {
-          state.promise = promise;
-        } else {
-          const newState = $state({ promise });
-          this.map.set(key, newState);
-        }
-      });
-
-      const resolve = (loadedInfos: Map<K, V>) => {
-        loadedInfos.forEach((loadedInfo, key) => {
-          const state = this.map.get(key)!;
-          if (state.value) {
-            Object.assign(state.value, loadedInfo);
-          } else {
-            state.value = loadedInfo;
-          }
-          newPromises.get(key)!.resolve(state.value);
-        });
-        return loadedInfos;
-      };
-
-      this.options.bulkFetchFromIndexedDB!(
-        new Set(newPromises.keys().filter((key) => this.map.get(key)!.value === undefined)),
-      )
-        .then(resolve)
-        .then(() =>
-          this.options.bulkFetchFromServer!(
-            new Map(
-              newPromises.keys().map((key) => [key, { cachedValue: this.map.get(key)!.value }]),
-            ),
-          ),
-        )
-        .then(resolve)
-        .finally(() => {
-          newPromises.forEach((_, key) => {
-            this.map.get(key)!.promise = undefined;
-          });
-        });
-
-      const bottleneckPromises = Array.from(
-        keys
-          .keys()
-          .filter((key) => this.map.get(key)!.value === undefined)
-          .map((key) => this.map.get(key)!.promise!),
-      );
-      const makeResult = () =>
-        new Map(keys.keys().map((key) => [key, this.map.get(key)!.value!] as const));
-      return bottleneckPromises.length > 0
-        ? Promise.all(bottleneckPromises).then(makeResult)
-        : makeResult();
-    });
-  }
-}
-
-const unwrapEntryDataKey = async (metadata: { mekVersion: number; dek: string }) => {
-  const { dataKey } = await unwrapDataKey(
-    metadata.dek,
-    keyring.getMasterKey(metadata.mekVersion).key,
-  );
-  return dataKey;
-};
-
-export const decryptDirectoryMetadata = async (metadata: {
-  mekVersion: number;
-  dek: string;
-  dekVersion: Date;
-  name: string;
-  nameIv: string;
-}) => {
-  const dataKey = await unwrapEntryDataKey(metadata);
-  const name = await decryptString(metadata.name, metadata.nameIv, dataKey);
-
-  return {
-    dataKey: { key: dataKey, version: metadata.dekVersion },
-    name,
-  };
-};
-
-const decryptDate = async (ciphertext: string, iv: string, dataKey: CryptoKey) => {
-  return new Date(parseInt(await decryptString(ciphertext, iv, dataKey), 10));
-};
-
-export const decryptFileMetadata = async (metadata: {
-  mekVersion: number;
-  dek: string;
-  dekVersion: Date;
-  name: string;
-  nameIv: string;
-  createdAt?: string;
-  createdAtIv?: string;
-  lastModifiedAt: string;
-  lastModifiedAtIv: string;
-}) => {
-  const dataKey = await unwrapEntryDataKey(metadata);
-  const [name, createdAt, lastModifiedAt] = await Promise.all([
-    decryptString(metadata.name, metadata.nameIv, dataKey),
-    metadata.createdAt
-      ? decryptDate(metadata.createdAt, metadata.createdAtIv!, dataKey)
-      : undefined,
-    decryptDate(metadata.lastModifiedAt, metadata.lastModifiedAtIv, dataKey),
-  ]);
-
-  return {
-    dataKey: { key: dataKey, version: metadata.dekVersion },
-    name,
-    createdAt,
-    lastModifiedAt,
-  };
-};
-
-export const decryptCategoryMetadata = decryptDirectoryMetadata;
diff --git a/src/lib/services/auth.ts b/src/lib/services/auth.ts
deleted file mode 100644
index 80ea2b6..0000000
--- a/src/lib/services/auth.ts
+++ /dev/null
@@ -1,11 +0,0 @@
-import { trpc } from "#trpc/client.js";
-
-export const requestLogout = async () => {
-  try {
-    await trpc.auth.logout.mutate();
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
-  }
-};
diff --git a/src/lib/services/category.ts b/src/lib/services/category.ts
deleted file mode 100644
index 270c5b3..0000000
--- a/src/lib/services/category.ts
+++ /dev/null
@@ -1,34 +0,0 @@
-import { keyring } from "#lib/client/keys/index.js";
-import { generateDataKey, wrapDataKey, encryptString } from "#lib/shared/crypto/index.js";
-import { trpc } from "#trpc/client.js";
-
-export const requestCategoryCreation = async (name: string, parentId: "root" | number) => {
-  const masterKey = keyring.activeMasterKey;
-  const { dataKey, dataKeyVersion } = await generateDataKey();
-  const nameEncrypted = await encryptString(name, dataKey);
-
-  try {
-    await trpc.category.create.mutate({
-      parent: parentId,
-      mekVersion: masterKey.version,
-      dek: await wrapDataKey(dataKey, masterKey.key),
-      dekVersion: dataKeyVersion,
-      name: nameEncrypted.ciphertext,
-      nameIv: nameEncrypted.iv,
-    });
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
-  }
-};
-
-export const requestFileRemovalFromCategory = async (fileId: number, categoryId: number) => {
-  try {
-    await trpc.category.removeFile.mutate({ id: categoryId, file: fileId });
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
-  }
-};
diff --git a/src/lib/services/file.ts b/src/lib/services/file.ts
deleted file mode 100644
index 6ffddb5..0000000
--- a/src/lib/services/file.ts
+++ /dev/null
@@ -1,64 +0,0 @@
-import {
-  getFileCache,
-  storeFileCache,
-  deleteFileCache,
-  deleteFileThumbnailCache,
-} from "#lib/client/cache/index.js";
-import { getAllFileInfos } from "#lib/client/storage/indexedDB/filesystem.js";
-import { uploadBlob } from "#lib/client/transfer/chunkedUpload.js";
-import { downloadFile } from "#lib/client/transfer/index.js";
-import { trpc } from "#trpc/client.js";
-
-export const requestFileDownload = async (
-  fileId: number,
-  dataKey: CryptoKey,
-  isLegacy: boolean,
-) => {
-  const cache = await getFileCache(fileId);
-  if (cache) return cache;
-
-  const fileBuffer = await downloadFile(fileId, dataKey, isLegacy);
-  storeFileCache(fileId, fileBuffer); // Intended
-  return fileBuffer;
-};
-
-export const requestFileThumbnailUpload = async (
-  fileId: number,
-  thumbnail: Blob,
-  dataKey: CryptoKey,
-  dataKeyVersion: Date,
-) => {
-  try {
-    const { uploadId } = await trpc.upload.startFileThumbnailUpload.mutate({
-      file: fileId,
-      dekVersion: dataKeyVersion,
-    });
-
-    await uploadBlob(uploadId, thumbnail, dataKey);
-
-    await trpc.upload.completeFileThumbnailUpload.mutate({ uploadId });
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
-  }
-};
-
-export const requestDeletedFilesCleanup = async () => {
-  let liveFiles;
-  try {
-    liveFiles = await trpc.file.list.query();
-  } catch {
-    // TODO: Error Handling
-    return;
-  }
-
-  const liveFilesSet = new Set(liveFiles);
-  const maybeCachedFiles = await getAllFileInfos();
-
-  await Promise.all(
-    maybeCachedFiles
-      .filter(({ id }) => !liveFilesSet.has(id))
-      .flatMap(({ id }) => [deleteFileCache(id), deleteFileThumbnailCache(id)]),
-  );
-};
diff --git a/src/lib/utils/concurrency/HybridPromise.ts b/src/lib/utils/concurrency/HybridPromise.ts
deleted file mode 100644
index 912a54c..0000000
--- a/src/lib/utils/concurrency/HybridPromise.ts
+++ /dev/null
@@ -1,131 +0,0 @@
-type MaybePromise<T> = T | Promise<T> | HybridPromise<T>;
-
-type HybridPromiseState<T> =
-  | { mode: "sync"; status: "fulfilled"; value: T }
-  | { mode: "sync"; status: "rejected"; reason: unknown }
-  | { mode: "async"; promise: Promise<T> };
-
-export class HybridPromise<T> implements PromiseLike<T> {
-  private isConsumed = false;
-
-  private constructor(private readonly state: HybridPromiseState<T>) {
-    if (state.mode === "sync" && state.status === "rejected") {
-      queueMicrotask(() => {
-        if (!this.isConsumed) {
-          throw state.reason;
-        }
-      });
-    }
-  }
-
-  isSync(): boolean {
-    return this.state.mode === "sync";
-  }
-
-  toPromise(): Promise<T> {
-    this.isConsumed = true;
-
-    if (this.state.mode === "async") return this.state.promise;
-    return this.state.status === "fulfilled"
-      ? Promise.resolve(this.state.value)
-      : Promise.reject(this.state.reason);
-  }
-
-  static resolve<T>(value: MaybePromise<T>): HybridPromise<T> {
-    if (value instanceof HybridPromise) return value;
-    return new HybridPromise(
-      value instanceof Promise
-        ? { mode: "async", promise: value }
-        : { mode: "sync", status: "fulfilled", value },
-    );
-  }
-
-  static reject<T = never>(reason?: unknown): HybridPromise<T> {
-    return new HybridPromise({ mode: "sync", status: "rejected", reason });
-  }
-
-  then<TResult1 = T, TResult2 = never>(
-    onfulfilled?: ((value: T) => MaybePromise<TResult1>) | null | undefined,
-    onrejected?: ((reason: unknown) => MaybePromise<TResult2>) | null | undefined,
-  ): HybridPromise<TResult1 | TResult2> {
-    this.isConsumed = true;
-
-    if (this.state.mode === "async") {
-      return new HybridPromise({
-        mode: "async",
-        promise: this.state.promise.then(onfulfilled, onrejected) as any,
-      });
-    }
-
-    try {
-      if (this.state.status === "fulfilled") {
-        if (!onfulfilled) return HybridPromise.resolve(this.state.value as any);
-        return HybridPromise.resolve(onfulfilled(this.state.value));
-      } else {
-        if (!onrejected) return HybridPromise.reject(this.state.reason);
-        return HybridPromise.resolve(onrejected(this.state.reason));
-      }
-    } catch (e) {
-      return HybridPromise.reject(e);
-    }
-  }
-
-  catch<TResult = never>(
-    onrejected?: ((reason: unknown) => MaybePromise<TResult>) | null | undefined,
-  ): HybridPromise<T | TResult> {
-    return this.then<T, TResult>(null, onrejected);
-  }
-
-  finally(onfinally?: (() => void) | null | undefined): HybridPromise<T> {
-    this.isConsumed = true;
-
-    if (this.state.mode === "async") {
-      return new HybridPromise({ mode: "async", promise: this.state.promise.finally(onfinally) });
-    }
-
-    try {
-      onfinally?.();
-      return new HybridPromise(this.state);
-    } catch (e) {
-      return HybridPromise.reject(e);
-    }
-  }
-
-  static all<T extends readonly unknown[] | []>(
-    maybePromises: T,
-  ): HybridPromise<{ -readonly [P in keyof T]: HybridAwaited<T[P]> }> {
-    const length = maybePromises.length;
-    if (length === 0) {
-      return HybridPromise.resolve([] as any);
-    }
-
-    const hps = Array.from(maybePromises).map((p) => HybridPromise.resolve(p));
-    if (hps.some((hp) => !hp.isSync())) {
-      return new HybridPromise({
-        mode: "async",
-        promise: Promise.all(hps.map((hp) => hp.toPromise())) as any,
-      });
-    }
-
-    try {
-      return HybridPromise.resolve(
-        Array.from(
-          hps.map((hp) => {
-            if (hp.state.mode === "sync") {
-              if (hp.state.status === "fulfilled") {
-                return hp.state.value;
-              } else {
-                throw hp.state.reason;
-              }
-            }
-          }),
-        ) as any,
-      );
-    } catch (e) {
-      return HybridPromise.reject(e);
-    }
-  }
-}
-
-export type HybridAwaited<T> =
-  T extends HybridPromise<infer U> ? U : T extends Promise<infer U> ? U : T;
diff --git a/src/lib/utils/concurrency/index.ts b/src/lib/utils/concurrency/index.ts
index 59fe81d..31b055c 100644
--- a/src/lib/utils/concurrency/index.ts
+++ b/src/lib/utils/concurrency/index.ts
@@ -1,3 +1,2 @@
 export * from "./BoundedQueue";
-export * from "./HybridPromise";
 export * from "./Scheduler";
diff --git a/src/routes/(fullscreen)/auth/changePassword/+page.svelte b/src/routes/(fullscreen)/auth/changePassword/+page.svelte
index e4668be..bd5e43f 100644
--- a/src/routes/(fullscreen)/auth/changePassword/+page.svelte
+++ b/src/routes/(fullscreen)/auth/changePassword/+page.svelte
@@ -2,7 +2,8 @@
   import { goto } from "$app/navigation";
   import { BottomDiv, Button, FullscreenDiv, TextInput } from "#lib/components/atoms/index.js";
   import { TitledDiv, TopBar } from "#lib/components/molecules/index.js";
-  import { requestPasswordChange } from "./service";
+  import { showToast, tryAction } from "#lib/client/toast.svelte.js";
+  import { changePassword as requestPasswordChange } from "#lib/features/auth/index.js";
 
   let oldPassword = $state("");
   let newPassword = $state("");
@@ -10,11 +11,16 @@
 
   const changePassword = async () => {
     if (newPassword !== confirmPassword) {
-      // TODO: Alert
+      showToast("새 비밀번호가 일치하지 않아요.");
       return;
     }
 
-    if (await requestPasswordChange(oldPassword, newPassword)) {
+    if (
+      await tryAction(
+        () => requestPasswordChange(oldPassword, newPassword),
+        "비밀번호를 바꾸지 못했어요. 기존 비밀번호를 확인해 주세요.",
+      )
+    ) {
       await goto("/menu");
     }
   };
diff --git a/src/routes/(fullscreen)/auth/changePassword/service.ts b/src/routes/(fullscreen)/auth/changePassword/service.ts
deleted file mode 100644
index 86c96f9..0000000
--- a/src/routes/(fullscreen)/auth/changePassword/service.ts
+++ /dev/null
@@ -1,11 +0,0 @@
-import { trpc } from "#trpc/client.js";
-
-export const requestPasswordChange = async (oldPassword: string, newPassword: string) => {
-  try {
-    await trpc.auth.changePassword.mutate({ oldPassword, newPassword });
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
-  }
-};
diff --git a/src/routes/(fullscreen)/auth/login/+page.svelte b/src/routes/(fullscreen)/auth/login/+page.svelte
index 59abf5a..98dbfc4 100644
--- a/src/routes/(fullscreen)/auth/login/+page.svelte
+++ b/src/routes/(fullscreen)/auth/login/+page.svelte
@@ -14,9 +14,10 @@
     keyring,
     requestClientRegistrationAndSessionUpgrade,
   } from "#lib/client/keys/index.js";
-  import { requestLogout } from "#lib/services/auth.js";
-  import { requestDeletedFilesCleanup } from "#lib/services/file.js";
-  import { requestLogin } from "./service";
+  import { showErrorToast, showToast } from "#lib/client/toast.svelte.js";
+  import { login as requestLogin, logout as requestLogout } from "#lib/features/auth/index.js";
+  import { cleanupDeletedFileCaches } from "#lib/features/filesystem/index.js";
+  import { isTRPCClientError } from "#trpc/client.js";
 
   let { data } = $props();
 
@@ -30,42 +31,45 @@
   };
 
   const upgradeSession = async (force: boolean) => {
-    try {
-      const [upgradeRes, upgradeError] = await requestClientRegistrationAndSessionUpgrade(force);
-      if (!force && upgradeError === "Already logged in") {
-        isForceLoginModalOpen = true;
-        return;
-      } else if (!upgradeRes) {
-        throw new Error("Failed to upgrade session");
-      }
+    const [upgradeRes, upgradeError] = await requestClientRegistrationAndSessionUpgrade(force);
+    if (!force && upgradeError === "Already logged in") {
+      isForceLoginModalOpen = true;
+      return;
+    } else if (!upgradeRes) {
+      showToast("로그인하지 못했어요.");
+      return;
+    }
 
-      // TODO: Multi-user support
+    // TODO: Multi-user support
 
-      if (keyring.hasMasterKeys || (await downloadMasterKeys())) {
-        await requestDeletedFilesCleanup();
-        await goto(data.redirectPath);
-      } else {
-        await redirect("/client/pending");
-      }
-    } catch (e) {
-      // TODO
-      throw e;
+    if (keyring.hasMasterKeys || (await downloadMasterKeys())) {
+      await cleanupDeletedFileCaches().catch(console.error);
+      await goto(data.redirectPath);
+    } else {
+      await redirect("/client/pending");
     }
   };
 
   const login = async () => {
-    // TODO: Validation
+    if (!email || !password) {
+      showToast("이메일과 비밀번호를 입력해 주세요.");
+      return;
+    }
 
     try {
-      if (!(await requestLogin(email, password))) throw new Error("Failed to login");
-
-      if (!keyring.clientKeys) return await redirect("/key/generate");
-
-      await upgradeSession(false);
+      await requestLogin(email, password);
     } catch (e) {
-      // TODO: Alert
-      throw e;
+      if (isTRPCClientError(e) && e.data?.code === "UNAUTHORIZED") {
+        showToast("이메일 또는 비밀번호가 올바르지 않아요.");
+      } else {
+        showErrorToast(e, "로그인하지 못했어요.");
+      }
+      return;
     }
+
+    if (!keyring.clientKeys) return await redirect("/key/generate");
+
+    await upgradeSession(false);
   };
 </script>
 
@@ -93,6 +97,6 @@
 
 <ForceLoginModal
   bind:isOpen={isForceLoginModalOpen}
-  oncancel={requestLogout}
+  oncancel={() => requestLogout().catch(console.error)}
   onLoginClick={() => upgradeSession(true)}
 />
diff --git a/src/routes/(fullscreen)/auth/login/service.ts b/src/routes/(fullscreen)/auth/login/service.ts
deleted file mode 100644
index 620e90b..0000000
--- a/src/routes/(fullscreen)/auth/login/service.ts
+++ /dev/null
@@ -1,11 +0,0 @@
-import { trpc } from "#trpc/client.js";
-
-export const requestLogin = async (email: string, password: string) => {
-  try {
-    await trpc.auth.login.mutate({ email, password });
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
-  }
-};
diff --git a/src/routes/(fullscreen)/file/[id]/+page.svelte b/src/routes/(fullscreen)/file/[id]/+page.svelte
index 59b5bcf..3562b0b 100644
--- a/src/routes/(fullscreen)/file/[id]/+page.svelte
+++ b/src/routes/(fullscreen)/file/[id]/+page.svelte
@@ -5,20 +5,22 @@
   import { page } from "$app/state";
   import { FullscreenDiv } from "#lib/components/atoms/index.js";
   import { Categories, IconEntryButton, TopBar } from "#lib/components/molecules/index.js";
-  import { getFileInfo, type MaybeFileInfo } from "#lib/modules/filesystem/index.js";
   import { captureVideoThumbnail } from "#lib/client/media/thumbnail.js";
   import { getFileDownloadState } from "#lib/client/transfer/index.js";
-  import { HybridPromise } from "#lib/utils/index.js";
+  import { showErrorToast, tryAction } from "#lib/client/toast.svelte.js";
+  import {
+    addFileToCategory,
+    getFileContent,
+    getFileStreamUrl,
+    removeFileFromCategory,
+    setFileFavorite,
+    uploadFileThumbnail,
+    useFile,
+    type DataKey,
+    type FileInfo,
+  } from "#lib/features/filesystem/index.js";
   import AddToCategoryBottomSheet from "./AddToCategoryBottomSheet.svelte";
   import DownloadStatus from "./DownloadStatus.svelte";
-  import {
-    requestFileRemovalFromCategory,
-    requestFileDownload,
-    requestThumbnailUpload,
-    requestFileAdditionToCategory,
-    requestVideoStream,
-    requestFavoriteToggle,
-  } from "./service";
   import TopBarMenu from "./TopBarMenu.svelte";
 
   import IconMoreVert from "~icons/material-symbols/more-vert";
@@ -28,7 +30,8 @@
 
   let { data } = $props();
 
-  let info: MaybeFileInfo | undefined = $state();
+  const file = useFile(() => data.id);
+  let info = $derived(file.current);
   let downloadState = $derived(getFileDownloadState(data.id));
 
   let isMenuOpen = $state(false);
@@ -59,33 +62,43 @@
     );
   };
 
-  const updateThumbnail = async (dataKey: CryptoKey, dataKeyVersion: Date) => {
-    const thumbnail = await captureVideoThumbnail(videoElement!);
-    await requestThumbnailUpload(data.id, thumbnail, dataKey, dataKeyVersion);
-  };
+  const updateThumbnail = (dataKey: DataKey) =>
+    tryAction(async () => {
+      const thumbnail = await captureVideoThumbnail(videoElement!);
+      await uploadFileThumbnail(data.id, thumbnail, dataKey);
+    }, "썸네일을 설정하지 못했어요.");
 
   const addToCategory = async (categoryId: number) => {
-    await requestFileAdditionToCategory(data.id, categoryId);
-    isAddToCategoryBottomSheetOpen = false;
-    void getFileInfo(data.id); // TODO: FIXME
+    if (
+      await tryAction(
+        () => addFileToCategory(data.id, categoryId),
+        "카테고리에 파일을 추가하지 못했어요.",
+      )
+    ) {
+      isAddToCategoryBottomSheetOpen = false;
+    }
   };
 
-  const removeFromCategory = async (categoryId: number) => {
-    await requestFileRemovalFromCategory(data.id, categoryId);
-    void getFileInfo(data.id); // TODO: FIXME
-  };
+  const removeFromCategory = (categoryId: number) =>
+    tryAction(
+      () => removeFileFromCategory(data.id, categoryId),
+      "카테고리에서 파일을 제거하지 못했어요.",
+    );
 
-  const toggleFavorite = async () => {
-    await requestFavoriteToggle(data.id, !!info?.isFavorite);
-    void getFileInfo(data.id); // TODO: FIXME
-  };
+  const toggleFavorite = () =>
+    tryAction(
+      () => setFileFavorite(info as FileInfo, !info?.isFavorite),
+      "즐겨찾기를 변경하지 못했어요.",
+    );
 
-  $effect(() => {
-    HybridPromise.resolve(getFileInfo(data.id)).then((result) => {
-      if (data.id === result.id) {
-        info = result;
-      }
+  const loadContent = (dataKey: CryptoKey, isLegacy: boolean) =>
+    getFileContent(data.id, dataKey, isLegacy).catch((e) => {
+      showErrorToast(e, "파일을 불러오지 못했어요.");
+      throw e;
     });
+
+  $effect.pre(() => {
+    void data.id; // Reset the viewer when navigating to another file
     isDownloadRequested = false;
     viewerType = undefined;
   });
@@ -103,25 +116,24 @@
         if (!downloadState && !isDownloadRequested) {
           isDownloadRequested = true;
 
-          if (viewerType === "video" && !info!.isLegacy) {
-            requestVideoStream(data.id, info!.dataKey!.key, contentType).then((streamUrl) => {
-              if (streamUrl) {
+          const { key } = info!.dataKey!;
+          const isLegacy = !!info!.isLegacy;
+          if (viewerType === "video" && !isLegacy) {
+            getFileStreamUrl(data.id, key, contentType)
+              .then((streamUrl) => {
                 videoStreamUrl = streamUrl;
-              } else {
-                requestFileDownload(data.id, info!.dataKey!.key, info!.isLegacy!).then((buffer) =>
-                  updateViewer(buffer, contentType),
-                );
+              })
+              .catch(async () => {
+                // Fall back to downloading the whole file
+                await updateViewer(await loadContent(key, isLegacy), contentType);
+              });
+          } else {
+            void loadContent(key, isLegacy).then(async (buffer) => {
+              const blob = await updateViewer(buffer, contentType);
+              if (!viewerType) {
+                FileSaver.saveAs(blob, info!.name);
               }
             });
-          } else {
-            requestFileDownload(data.id, info!.dataKey!.key, info!.isLegacy!).then(
-              async (buffer) => {
-                const blob = await updateViewer(buffer, contentType);
-                if (!viewerType) {
-                  FileSaver.saveAs(blob, info!.name);
-                }
-              },
-            );
           }
         }
       });
@@ -192,7 +204,7 @@
               ></video>
               <IconEntryButton
                 icon={IconCamera}
-                onclick={() => updateThumbnail(info?.dataKey?.key!, info?.dataKey?.version!)}
+                onclick={() => updateThumbnail(info!.dataKey!)}
                 class="w-full"
               >
                 이 장면을 썸네일로 설정하기
diff --git a/src/routes/(fullscreen)/file/[id]/AddToCategoryBottomSheet.svelte b/src/routes/(fullscreen)/file/[id]/AddToCategoryBottomSheet.svelte
index 69ac8cc..b2bb9c0 100644
--- a/src/routes/(fullscreen)/file/[id]/AddToCategoryBottomSheet.svelte
+++ b/src/routes/(fullscreen)/file/[id]/AddToCategoryBottomSheet.svelte
@@ -2,9 +2,8 @@
   import { BottomDiv, BottomSheet, Button, FullscreenDiv } from "#lib/components/atoms/index.js";
   import { SubCategories } from "#lib/components/molecules/index.js";
   import { CategoryCreateModal } from "#lib/components/organisms/index.js";
-  import { getCategoryInfo, type MaybeCategoryInfo } from "#lib/modules/filesystem/index.js";
-  import { HybridPromise } from "#lib/utils/index.js";
-  import { requestCategoryCreation } from "./service";
+  import { tryAction } from "#lib/client/toast.svelte.js";
+  import { createCategory, useCategory } from "#lib/features/filesystem/index.js";
 
   interface Props {
     onAddToCategoryClick: (categoryId: number) => void;
@@ -13,13 +12,15 @@
 
   let { onAddToCategoryClick, isOpen = $bindable() }: Props = $props();
 
-  let categoryInfo: MaybeCategoryInfo | undefined = $state();
+  let categoryId: CategoryId = $state("root");
+  const category = useCategory(() => categoryId);
+  let categoryInfo = $derived(category.current);
 
   let isCategoryCreateModalOpen = $state(false);
 
-  $effect(() => {
+  $effect.pre(() => {
     if (isOpen) {
-      HybridPromise.resolve(getCategoryInfo("root")).then((result) => (categoryInfo = result));
+      categoryId = "root";
     }
   });
 </script>
@@ -30,8 +31,7 @@
       <SubCategories
         class="py-4"
         info={categoryInfo}
-        onSubCategoryClick={({ id }) =>
-          HybridPromise.resolve(getCategoryInfo(id)).then((result) => (categoryInfo = result))}
+        onSubCategoryClick={({ id }) => (categoryId = id)}
         onSubCategoryCreateClick={() => (isCategoryCreateModalOpen = true)}
         subCategoryCreatePosition="top"
       />
@@ -48,11 +48,6 @@
 
 <CategoryCreateModal
   bind:isOpen={isCategoryCreateModalOpen}
-  onCreateClick={async (name: string) => {
-    if (await requestCategoryCreation(name, categoryInfo!.id)) {
-      void getCategoryInfo(categoryInfo!.id); // TODO: FIXME
-      return true;
-    }
-    return false;
-  }}
+  onCreateClick={(name: string) =>
+    tryAction(() => createCategory(categoryId, name), "카테고리를 만들지 못했어요.")}
 />
diff --git a/src/routes/(fullscreen)/file/[id]/service.ts b/src/routes/(fullscreen)/file/[id]/service.ts
deleted file mode 100644
index d562940..0000000
--- a/src/routes/(fullscreen)/file/[id]/service.ts
+++ /dev/null
@@ -1,64 +0,0 @@
-import { storeFileThumbnailCache } from "#lib/client/cache/index.js";
-import { prepareFileDecryption, getDecryptedFileUrl } from "#lib/client/serviceWorker.js";
-import { requestFileThumbnailUpload } from "#lib/services/file.js";
-import { trpc } from "#trpc/client.js";
-
-export { requestCategoryCreation, requestFileRemovalFromCategory } from "#lib/services/category.js";
-export { requestFileDownload } from "#lib/services/file.js";
-
-export const requestVideoStream = async (
-  fileId: number,
-  dataKey: CryptoKey,
-  contentType: string,
-) => {
-  const res = await fetch(`/api/file/${fileId}/download`, { method: "HEAD" });
-  if (!res.ok) return null;
-
-  const encContentSize = parseInt(res.headers.get("Content-Length") ?? "0", 10);
-  if (encContentSize <= 0) return null;
-
-  try {
-    await prepareFileDecryption(fileId, { isLegacy: false, dataKey, encContentSize, contentType });
-    return getDecryptedFileUrl(fileId);
-  } catch {
-    // TODO: Error Handling
-    return null;
-  }
-};
-
-export const requestThumbnailUpload = async (
-  fileId: number,
-  thumbnail: Blob,
-  dataKey: CryptoKey,
-  dataKeyVersion: Date,
-) => {
-  const res = await requestFileThumbnailUpload(fileId, thumbnail, dataKey, dataKeyVersion);
-  if (!res) return false;
-
-  void thumbnail.arrayBuffer().then((buffer) => storeFileThumbnailCache(fileId, buffer));
-  return true;
-};
-
-export const requestFileAdditionToCategory = async (fileId: number, categoryId: number) => {
-  try {
-    await trpc.category.addFile.mutate({ id: categoryId, file: fileId });
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
-  }
-};
-
-export const requestFavoriteToggle = async (fileId: number, isFavorite: boolean) => {
-  try {
-    if (isFavorite) {
-      await trpc.favorites.removeFile.mutate({ id: fileId });
-    } else {
-      await trpc.favorites.addFile.mutate({ id: fileId });
-    }
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
-  }
-};
diff --git a/src/routes/(fullscreen)/file/downloads/+page.svelte b/src/routes/(fullscreen)/file/downloads/+page.svelte
index 0f6c766..4a3833b 100644
--- a/src/routes/(fullscreen)/file/downloads/+page.svelte
+++ b/src/routes/(fullscreen)/file/downloads/+page.svelte
@@ -7,7 +7,7 @@
     clearDownloadedFiles,
     type FileDownloadState,
   } from "#lib/client/transfer/index.js";
-  import { bulkGetFileInfo, type MaybeFileInfo } from "#lib/modules/filesystem/index.js";
+  import { bulkGetFileInfo, type MaybeFileInfo } from "#lib/features/filesystem/index.js";
   import File from "./File.svelte";
 
   let downloadingFiles: { info: MaybeFileInfo; state: FileDownloadState }[] = $state([]);
diff --git a/src/routes/(fullscreen)/file/downloads/File.svelte b/src/routes/(fullscreen)/file/downloads/File.svelte
index d8bc3d4..f5494af 100644
--- a/src/routes/(fullscreen)/file/downloads/File.svelte
+++ b/src/routes/(fullscreen)/file/downloads/File.svelte
@@ -1,6 +1,6 @@
 <script lang="ts">
   import type { FileDownloadState } from "#lib/client/transfer/index.js";
-  import type { SummarizedFileInfo } from "#lib/modules/filesystem/index.js";
+  import type { SummarizedFileInfo } from "#lib/features/filesystem/index.js";
   import { formatNetworkSpeed } from "#lib/utils/index.js";
 
   import IconCloud from "~icons/material-symbols/cloud";
diff --git a/src/routes/(fullscreen)/gallery/+page.svelte b/src/routes/(fullscreen)/gallery/+page.svelte
index 4e7dc04..f654918 100644
--- a/src/routes/(fullscreen)/gallery/+page.svelte
+++ b/src/routes/(fullscreen)/gallery/+page.svelte
@@ -11,7 +11,7 @@
     bulkGetFileInfo,
     type MaybeFileInfo,
     type SummarizedFileInfo,
-  } from "#lib/modules/filesystem/index.js";
+  } from "#lib/features/filesystem/index.js";
   import { formatDate, formatDateSortable, SortBy, sortEntries } from "#lib/utils/index.js";
 
   let { data } = $props();
diff --git a/src/routes/(fullscreen)/key/export/+page.svelte b/src/routes/(fullscreen)/key/export/+page.svelte
index b668ad9..ec357a4 100644
--- a/src/routes/(fullscreen)/key/export/+page.svelte
+++ b/src/routes/(fullscreen)/key/export/+page.svelte
@@ -10,6 +10,7 @@
     requestSessionUpgrade,
     serializeClientKeys,
   } from "#lib/client/keys/index.js";
+  import { showToast } from "#lib/client/toast.svelte.js";
   import BeforeContinueBottomSheet from "./BeforeContinueBottomSheet.svelte";
   import BeforeContinueModal from "./BeforeContinueModal.svelte";
 
@@ -33,26 +34,26 @@
   };
 
   const registerPubKeys = async () => {
-    try {
-      if (!(await requestClientRegistration())) throw new Error("Failed to register client");
-
-      await keyring.persistClientKeys();
-
-      if (!(await requestSessionUpgrade())[0]) throw new Error("Failed to upgrade session");
-
-      if (
-        !(await registerInitialMasterKeyAndHmacSecret(
-          data.masterKeyWrapped,
-          data.hmacSecretWrapped,
-        ))
-      )
-        throw new Error("Failed to register initial MEK and HSK");
-
-      await goto("/client/pending?redirect=" + encodeURIComponent(data.redirectPath));
-    } catch (e) {
-      // TODO: Error handling
-      throw e;
+    if (!(await requestClientRegistration())) {
+      showToast("이 디바이스를 등록하지 못했어요.");
+      return;
     }
+
+    await keyring.persistClientKeys();
+
+    if (!(await requestSessionUpgrade())[0]) {
+      showToast("로그인하지 못했어요.");
+      return;
+    }
+
+    if (
+      !(await registerInitialMasterKeyAndHmacSecret(data.masterKeyWrapped, data.hmacSecretWrapped))
+    ) {
+      showToast("암호 키를 등록하지 못했어요.");
+      return;
+    }
+
+    await goto("/client/pending?redirect=" + encodeURIComponent(data.redirectPath));
   };
 </script>
 
diff --git a/src/routes/(fullscreen)/key/generate/+page.svelte b/src/routes/(fullscreen)/key/generate/+page.svelte
index 3e79117..e7624bf 100644
--- a/src/routes/(fullscreen)/key/generate/+page.svelte
+++ b/src/routes/(fullscreen)/key/generate/+page.svelte
@@ -13,7 +13,8 @@
     registerInitialMasterKeyAndHmacSecret,
     requestClientRegistrationAndSessionUpgrade,
   } from "#lib/client/keys/index.js";
-  import { requestDeletedFilesCleanup } from "#lib/services/file.js";
+  import { showToast } from "#lib/client/toast.svelte.js";
+  import { cleanupDeletedFileCaches } from "#lib/features/filesystem/index.js";
   import { gotoStateful } from "#lib/utils/index.js";
   import Order from "./Order.svelte";
 
@@ -46,8 +47,6 @@
   ];
 
   const generateKeys = async () => {
-    // TODO: Loading indicator
-
     const { encryptKey, ...clientKeys } = await generateClientKeys();
     const { masterKey, masterKeyWrapped } = await generateInitialMasterKey(encryptKey);
     const { hmacSecretWrapped } = await generateInitialHmacSecret(masterKey);
@@ -66,7 +65,7 @@
       isForceLoginModalOpen = true;
       return;
     } else if (!upgradeRes) {
-      // TODO: Error Handling
+      showToast("이 디바이스를 등록하지 못했어요.");
       return;
     }
 
@@ -78,11 +77,11 @@
     await keyring.persistClientKeys();
 
     if (!(await registerInitialMasterKeyAndHmacSecret(masterKeyWrapped, hmacSecretWrapped))) {
-      // TODO: Error Handling
+      showToast("암호 키를 등록하지 못했어요.");
       return;
     }
 
-    await requestDeletedFilesCleanup();
+    await cleanupDeletedFileCaches().catch(console.error);
     await goto("/client/pending?redirect=" + encodeURIComponent(data.redirectPath));
   };
 
@@ -90,10 +89,10 @@
     const file = fileInput?.files?.[0];
     if (!file) return;
 
-    if (await importClientKeys(await file.text())) {
+    if (await importClientKeys(await file.text()).catch(() => false)) {
       await upgradeSession(false);
     } else {
-      // TODO: Error Handling
+      showToast("올바른 암호 키 파일이 아니에요.");
     }
 
     fileInput!.value = "";
diff --git a/src/routes/(fullscreen)/search/+page.svelte b/src/routes/(fullscreen)/search/+page.svelte
index 5d7ab53..e45440a 100644
--- a/src/routes/(fullscreen)/search/+page.svelte
+++ b/src/routes/(fullscreen)/search/+page.svelte
@@ -5,17 +5,18 @@
   import { slide } from "svelte/transition";
   import { goto } from "$app/navigation";
   import { Chip, FullscreenDiv, RowVirtualizer } from "#lib/components/atoms/index.js";
+  import { showErrorToast } from "#lib/client/toast.svelte.js";
   import {
     getDirectoryInfo,
     type LocalCategoryInfo,
     type MaybeDirectoryInfo,
-  } from "#lib/modules/filesystem/index.js";
-  import { HybridPromise, searchString, sortEntries } from "#lib/utils/index.js";
+  } from "#lib/features/filesystem/index.js";
+  import { search, type SearchFilter, type SearchResult } from "#lib/features/search/index.js";
+  import { searchString, sortEntries } from "#lib/utils/index.js";
   import Directory from "./Directory.svelte";
   import File from "./File.svelte";
   import SearchBar from "./SearchBar.svelte";
   import SelectCategoryBottomSheet from "./SelectCategoryBottomSheet.svelte";
-  import { requestSearch, type SearchFilter, type SearchResult } from "./service";
 
   let { data } = $props();
 
@@ -121,10 +122,18 @@
 
   $effect.pre(() => {
     if (data.directoryId) {
-      HybridPromise.resolve(getDirectoryInfo(data.directoryId)).then((res) => {
+      const applyDirectoryInfo = (res: MaybeDirectoryInfo) => {
         directoryInfo = res;
         filters.searchInDirectory = res.exists;
-      });
+      };
+
+      // Apply synchronously if cached so that a restored snapshot isn't overwritten later
+      const res = getDirectoryInfo(data.directoryId);
+      if (res instanceof Promise) {
+        res.then(applyDirectoryInfo).catch(() => {});
+      } else {
+        applyDirectoryInfo(res);
+      }
     } else {
       directoryInfo = undefined;
       filters.searchInDirectory = false;
@@ -148,13 +157,15 @@
     }
 
     if (hasAnyFilter) {
-      requestSearch({
+      search({
         ancestorId: filters.searchInDirectory ? data.directoryId! : "root",
         inFavorites: filters.searchInFavorites,
         categories: filters.categories,
-      }).then((res) => {
-        serverResult = res;
-      });
+      })
+        .then((res) => {
+          serverResult = res;
+        })
+        .catch((e) => showErrorToast(e, "검색하지 못했어요."));
     }
   });
 </script>
diff --git a/src/routes/(fullscreen)/search/Directory.svelte b/src/routes/(fullscreen)/search/Directory.svelte
index 48e3833..09fd876 100644
--- a/src/routes/(fullscreen)/search/Directory.svelte
+++ b/src/routes/(fullscreen)/search/Directory.svelte
@@ -1,7 +1,7 @@
 <script lang="ts">
   import { ActionEntryButton } from "#lib/components/atoms/index.js";
   import { DirectoryEntryLabel } from "#lib/components/molecules/index.js";
-  import type { SubDirectoryInfo } from "#lib/modules/filesystem/index.js";
+  import type { SubDirectoryInfo } from "#lib/features/filesystem/index.js";
 
   interface Props {
     info: SubDirectoryInfo;
diff --git a/src/routes/(fullscreen)/search/File.svelte b/src/routes/(fullscreen)/search/File.svelte
index 1692d78..d87b708 100644
--- a/src/routes/(fullscreen)/search/File.svelte
+++ b/src/routes/(fullscreen)/search/File.svelte
@@ -2,7 +2,7 @@
   import { ActionEntryButton } from "#lib/components/atoms/index.js";
   import { DirectoryEntryLabel } from "#lib/components/molecules/index.js";
   import { getFileThumbnail } from "#lib/client/cache/index.js";
-  import type { SummarizedFileInfo } from "#lib/modules/filesystem/index.js";
+  import type { SummarizedFileInfo } from "#lib/features/filesystem/index.js";
   import { formatDateTime } from "#lib/utils/index.js";
 
   interface Props {
diff --git a/src/routes/(fullscreen)/search/SelectCategoryBottomSheet.svelte b/src/routes/(fullscreen)/search/SelectCategoryBottomSheet.svelte
index 4b17e1d..d07aa84 100644
--- a/src/routes/(fullscreen)/search/SelectCategoryBottomSheet.svelte
+++ b/src/routes/(fullscreen)/search/SelectCategoryBottomSheet.svelte
@@ -1,12 +1,7 @@
 <script lang="ts">
   import { BottomDiv, BottomSheet, Button, FullscreenDiv } from "#lib/components/atoms/index.js";
   import { SubCategories } from "#lib/components/molecules/index.js";
-  import {
-    getCategoryInfo,
-    type LocalCategoryInfo,
-    type MaybeCategoryInfo,
-  } from "#lib/modules/filesystem/index.js";
-  import { HybridPromise } from "#lib/utils/index.js";
+  import { useCategory, type LocalCategoryInfo } from "#lib/features/filesystem/index.js";
 
   interface Props {
     isOpen: boolean;
@@ -16,11 +11,13 @@
 
   let { isOpen = $bindable(), mode, onSelectCategoryClick }: Props = $props();
 
-  let categoryInfo: MaybeCategoryInfo | undefined = $state();
+  let categoryId: CategoryId = $state("root");
+  const category = useCategory(() => categoryId);
+  let categoryInfo = $derived(category.current);
 
-  $effect(() => {
+  $effect.pre(() => {
     if (isOpen) {
-      HybridPromise.resolve(getCategoryInfo("root")).then((result) => (categoryInfo = result));
+      categoryId = "root";
     }
   });
 </script>
@@ -31,8 +28,7 @@
       <SubCategories
         class="py-4"
         info={categoryInfo}
-        onSubCategoryClick={({ id }) =>
-          HybridPromise.resolve(getCategoryInfo(id)).then((result) => (categoryInfo = result))}
+        onSubCategoryClick={({ id }) => (categoryId = id)}
       />
       {#if categoryInfo.id !== "root"}
         <BottomDiv>
diff --git a/src/routes/(fullscreen)/settings/cache/+page.svelte b/src/routes/(fullscreen)/settings/cache/+page.svelte
index 062073f..c24d936 100644
--- a/src/routes/(fullscreen)/settings/cache/+page.svelte
+++ b/src/routes/(fullscreen)/settings/cache/+page.svelte
@@ -7,7 +7,7 @@
     getFileCacheIndex,
     deleteFileCache as doDeleteFileCache,
   } from "#lib/client/cache/index.js";
-  import { bulkGetFileInfo, type MaybeFileInfo } from "#lib/modules/filesystem/index.js";
+  import { bulkGetFileInfo, type MaybeFileInfo } from "#lib/features/filesystem/index.js";
   import { formatFileSize } from "#lib/utils/index.js";
   import File from "./File.svelte";
 
diff --git a/src/routes/(fullscreen)/settings/cache/File.svelte b/src/routes/(fullscreen)/settings/cache/File.svelte
index 1724f5c..501c6db 100644
--- a/src/routes/(fullscreen)/settings/cache/File.svelte
+++ b/src/routes/(fullscreen)/settings/cache/File.svelte
@@ -1,6 +1,6 @@
 <script lang="ts">
   import type { FileCacheIndex } from "#lib/client/storage/indexedDB/index.js";
-  import type { MaybeFileInfo } from "#lib/modules/filesystem/index.js";
+  import type { MaybeFileInfo } from "#lib/features/filesystem/index.js";
   import { formatDate, formatFileSize } from "#lib/utils/index.js";
 
   import IconDraft from "~icons/material-symbols/draft";
diff --git a/src/routes/(fullscreen)/settings/thumbnail/+page.svelte b/src/routes/(fullscreen)/settings/thumbnail/+page.svelte
index fda73eb..5b92194 100644
--- a/src/routes/(fullscreen)/settings/thumbnail/+page.svelte
+++ b/src/routes/(fullscreen)/settings/thumbnail/+page.svelte
@@ -4,7 +4,7 @@
   import { BottomDiv, Button, FullscreenDiv } from "#lib/components/atoms/index.js";
   import { IconEntryButton, TopBar } from "#lib/components/molecules/index.js";
   import { deleteAllFileThumbnailCaches } from "#lib/client/cache/index.js";
-  import type { MaybeFileInfo } from "#lib/modules/filesystem/index.js";
+  import type { MaybeFileInfo } from "#lib/features/filesystem/index.js";
   import { sortEntries } from "#lib/utils/index.js";
   import File from "./File.svelte";
   import {
diff --git a/src/routes/(fullscreen)/settings/thumbnail/File.svelte b/src/routes/(fullscreen)/settings/thumbnail/File.svelte
index d5a6626..0e65d2e 100644
--- a/src/routes/(fullscreen)/settings/thumbnail/File.svelte
+++ b/src/routes/(fullscreen)/settings/thumbnail/File.svelte
@@ -11,7 +11,7 @@
 <script lang="ts">
   import { ActionEntryButton } from "#lib/components/atoms/index.js";
   import { DirectoryEntryLabel } from "#lib/components/molecules/index.js";
-  import type { FileInfo } from "#lib/modules/filesystem/index.js";
+  import type { FileInfo } from "#lib/features/filesystem/index.js";
   import { formatDateTime } from "#lib/utils/index.js";
   import type { GenerationStatus } from "./service";
 
diff --git a/src/routes/(fullscreen)/settings/thumbnail/service.ts b/src/routes/(fullscreen)/settings/thumbnail/service.ts
index 7be80f5..d4393da 100644
--- a/src/routes/(fullscreen)/settings/thumbnail/service.ts
+++ b/src/routes/(fullscreen)/settings/thumbnail/service.ts
@@ -1,10 +1,13 @@
 import { limitFunction } from "p-limit";
 import { SvelteMap } from "svelte/reactivity";
-import { storeFileThumbnailCache } from "#lib/client/cache/index.js";
 import { generateThumbnail } from "#lib/client/media/thumbnail.js";
-import { getFileInfo, type FileInfo } from "#lib/modules/filesystem/index.js";
-import { requestFileDownload, requestFileThumbnailUpload } from "#lib/services/file.js";
-import { HybridPromise, Scheduler } from "#lib/utils/index.js";
+import {
+  getFileContent,
+  getFileInfo,
+  uploadFileThumbnail,
+  type FileInfo,
+} from "#lib/features/filesystem/index.js";
+import { Scheduler } from "#lib/utils/index.js";
 import type { RouterOutputs } from "#trpc/router.server.js";
 
 export type GenerationStatus =
@@ -28,34 +31,26 @@ export const clearThumbnailGenerationStatuses = () => {
 export const requestMissingThumbnailFiles = async (
   filesRaw: RouterOutputs["file"]["listWithoutThumbnail"],
 ) => {
-  const files = await HybridPromise.all(
+  const files = await Promise.all(
     filesRaw.map((file) => getFileInfo(file.id, { serverResponse: file })),
   );
   return files;
 };
 
-const requestThumbnailUpload = limitFunction(
+const generateAndUploadThumbnail = limitFunction(
   async (fileInfo: FileInfo, fileBuffer: ArrayBuffer) => {
     statuses.set(fileInfo.id, "generating");
 
     const thumbnail = await generateThumbnail(
       new Blob([fileBuffer], { type: fileInfo.contentType }),
     );
-    if (!thumbnail) return false;
+    if (!thumbnail) {
+      throw new Error("Failed to generate thumbnail");
+    }
 
     statuses.set(fileInfo.id, "uploading");
-
-    const res = await requestFileThumbnailUpload(
-      fileInfo.id,
-      thumbnail,
-      fileInfo.dataKey?.key!,
-      fileInfo.dataKey?.version!,
-    );
-    if (!res) return false;
-
+    await uploadFileThumbnail(fileInfo.id, thumbnail, fileInfo.dataKey!);
     statuses.set(fileInfo.id, "uploaded");
-    void thumbnail.arrayBuffer().then((buffer) => storeFileThumbnailCache(fileInfo.id, buffer));
-    return true;
   },
   { concurrency: 4 },
 );
@@ -74,17 +69,13 @@ export const requestThumbnailGeneration = async (fileInfo: FileInfo) => {
     await scheduler.schedule(
       async () => {
         statuses.set(fileInfo.id, "generation-pending");
-        file = await requestFileDownload(fileInfo.id, fileInfo.dataKey?.key!, fileInfo.isLegacy!);
+        file = await getFileContent(fileInfo.id, fileInfo.dataKey!.key, !!fileInfo.isLegacy);
         return file.byteLength;
       },
-      async () => {
-        if (!(await requestThumbnailUpload(fileInfo, file!))) {
-          statuses.set(fileInfo.id, "error");
-        }
-      },
+      () => generateAndUploadThumbnail(fileInfo, file!),
     );
   } catch (e) {
+    console.error(e);
     statuses.set(fileInfo.id, "error");
-    throw e;
   }
 };
diff --git a/src/routes/(main)/category/[[id]]/+page.svelte b/src/routes/(main)/category/[[id]]/+page.svelte
index f971dfc..f4c970d 100644
--- a/src/routes/(main)/category/[[id]]/+page.svelte
+++ b/src/routes/(main)/category/[[id]]/+page.svelte
@@ -3,36 +3,36 @@
   import { CheckBox, RowVirtualizer } from "#lib/components/atoms/index.js";
   import { SubCategories, TopBar } from "#lib/components/molecules/index.js";
   import { CategoryCreateModal } from "#lib/components/organisms/index.js";
-  import { updateCategoryInfo } from "#lib/client/storage/indexedDB/index.js";
-  import { getCategoryInfo, type MaybeCategoryInfo } from "#lib/modules/filesystem/index.js";
-  import { HybridPromise, sortEntries } from "#lib/utils/index.js";
+  import { tryAction } from "#lib/client/toast.svelte.js";
+  import {
+    createCategory,
+    deleteCategory,
+    removeFileFromCategory,
+    renameCategory,
+    setCategoryFileRecursive,
+    useCategory,
+    type LocalCategoryInfo,
+  } from "#lib/features/filesystem/index.js";
+  import { sortEntries } from "#lib/utils/index.js";
   import CategoryDeleteModal from "./CategoryDeleteModal.svelte";
   import CategoryMenuBottomSheet from "./CategoryMenuBottomSheet.svelte";
   import CategoryRenameModal from "./CategoryRenameModal.svelte";
   import File from "./File.svelte";
-  import {
-    createContext,
-    requestCategoryCreation,
-    requestFileRemovalFromCategory,
-    requestCategoryRename,
-    requestCategoryDeletion,
-  } from "./service.svelte";
+  import { createContext } from "./service.svelte";
 
   import IconMoreVert from "~icons/material-symbols/more-vert";
 
   let { data } = $props();
   let context = createContext();
 
-  let info: MaybeCategoryInfo | undefined = $state();
+  const category = useCategory(() => data.id);
+  let info = $derived(category.current);
 
   let isCategoryCreateModalOpen = $state(false);
   let isCategoryMenuBottomSheetOpen = $state(false);
   let isCategoryRenameModalOpen = $state(false);
   let isCategoryDeleteModalOpen = $state(false);
 
-  let lastCategoryId: CategoryId | undefined = $state();
-  let lastIsFileRecursive: boolean | undefined = $state();
-
   let files = $derived(
     sortEntries(
       info?.files
@@ -40,27 +40,6 @@
         .filter(({ details }) => info?.isFileRecursive || !details.isRecursive) ?? [],
     ),
   );
-
-  $effect(() => {
-    if (!info || info.id === "root" || info.isFileRecursive === undefined) return;
-    if (lastCategoryId !== info.id) {
-      lastCategoryId = info.id;
-      lastIsFileRecursive = info.isFileRecursive;
-      return;
-    }
-    if (lastIsFileRecursive === info.isFileRecursive) return;
-
-    lastIsFileRecursive = info.isFileRecursive;
-    void updateCategoryInfo(info.id, { isFileRecursive: info.isFileRecursive });
-  });
-
-  $effect(() => {
-    HybridPromise.resolve(getCategoryInfo(data.id)).then((result) => {
-      if (data.id === result.id) {
-        info = result;
-      }
-    });
-  });
 </script>
 
 <svelte:head>
@@ -93,7 +72,12 @@
         <div class="space-y-2 bg-white p-4">
           <div class="flex items-center justify-between">
             <p class="text-lg font-bold text-gray-800">파일</p>
-            <CheckBox bind:checked={info.isFileRecursive}>
+            <CheckBox
+              bind:checked={
+                () => info.isFileRecursive,
+                (value) => setCategoryFileRecursive(info as LocalCategoryInfo, value)
+              }
+            >
               <p class="font-medium">하위 카테고리의 파일</p>
             </CheckBox>
           </div>
@@ -109,10 +93,11 @@
                 info={details}
                 onclick={({ id }) => goto(`/file/${id}?from=category`)}
                 onRemoveClick={!details.isRecursive
-                  ? async ({ id }) => {
-                      await requestFileRemovalFromCategory(id, data.id as number);
-                      void getCategoryInfo(data.id); // TODO: FIXME
-                    }
+                  ? ({ id }) =>
+                      tryAction(
+                        () => removeFileFromCategory(id, data.id as number),
+                        "카테고리에서 파일을 제거하지 못했어요.",
+                      )
                   : undefined}
               />
             {/snippet}
@@ -128,13 +113,8 @@
 
 <CategoryCreateModal
   bind:isOpen={isCategoryCreateModalOpen}
-  onCreateClick={async (name: string) => {
-    if (await requestCategoryCreation(name, data.id)) {
-      void getCategoryInfo(data.id); // TODO: FIXME
-      return true;
-    }
-    return false;
-  }}
+  onCreateClick={(name: string) =>
+    tryAction(() => createCategory(data.id, name), "카테고리를 만들지 못했어요.")}
 />
 
 <CategoryMenuBottomSheet
@@ -150,21 +130,17 @@
 />
 <CategoryRenameModal
   bind:isOpen={isCategoryRenameModalOpen}
-  onRenameClick={async (newName: string) => {
-    if (await requestCategoryRename(context.selectedCategory!, newName)) {
-      void getCategoryInfo(data.id); // TODO: FIXME
-      return true;
-    }
-    return false;
-  }}
+  onRenameClick={(newName: string) =>
+    tryAction(
+      () => renameCategory({ ...context.selectedCategory!, parentId: data.id }, newName),
+      "이름을 바꾸지 못했어요.",
+    )}
 />
 <CategoryDeleteModal
   bind:isOpen={isCategoryDeleteModalOpen}
-  onDeleteClick={async () => {
-    if (await requestCategoryDeletion(context.selectedCategory!)) {
-      void getCategoryInfo(data.id); // TODO: FIXME
-      return true;
-    }
-    return false;
-  }}
+  onDeleteClick={() =>
+    tryAction(
+      () => deleteCategory({ ...context.selectedCategory!, parentId: data.id }),
+      "카테고리를 삭제하지 못했어요.",
+    )}
 />
diff --git a/src/routes/(main)/category/[[id]]/File.svelte b/src/routes/(main)/category/[[id]]/File.svelte
index 363cd6d..02906b8 100644
--- a/src/routes/(main)/category/[[id]]/File.svelte
+++ b/src/routes/(main)/category/[[id]]/File.svelte
@@ -2,7 +2,7 @@
   import { ActionEntryButton } from "#lib/components/atoms/index.js";
   import { DirectoryEntryLabel } from "#lib/components/molecules/index.js";
   import { getFileThumbnail } from "#lib/client/cache/index.js";
-  import type { CategoryFileInfo } from "#lib/modules/filesystem/index.js";
+  import type { CategoryFileInfo } from "#lib/features/filesystem/index.js";
   import { formatDateTime } from "#lib/utils/index.js";
   import type { SelectedFile } from "./service.svelte";
 
diff --git a/src/routes/(main)/category/[[id]]/service.svelte.ts b/src/routes/(main)/category/[[id]]/service.svelte.ts
index 9a89c4f..7b3d105 100644
--- a/src/routes/(main)/category/[[id]]/service.svelte.ts
+++ b/src/routes/(main)/category/[[id]]/service.svelte.ts
@@ -1,9 +1,5 @@
 import { getContext, setContext } from "svelte";
 import type { SelectedCategory } from "#lib/components/molecules/index.js";
-import { encryptString } from "#lib/shared/crypto/index.js";
-import { trpc } from "#trpc/client.js";
-
-export { requestCategoryCreation, requestFileRemovalFromCategory } from "#lib/services/category.js";
 
 export interface SelectedFile {
   id: number;
@@ -20,35 +16,3 @@ export const createContext = () => {
 export const useContext = () => {
   return getContext<ReturnType<typeof createContext>>("context");
 };
-
-export const requestCategoryRename = async (category: SelectedCategory, newName: string) => {
-  if (!category.dataKey) {
-    // TODO: Error Handling
-    return false;
-  }
-
-  const newNameEncrypted = await encryptString(newName, category.dataKey.key);
-
-  try {
-    await trpc.category.rename.mutate({
-      id: category.id,
-      dekVersion: category.dataKey.version,
-      name: newNameEncrypted.ciphertext,
-      nameIv: newNameEncrypted.iv,
-    });
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
-  }
-};
-
-export const requestCategoryDeletion = async (category: SelectedCategory) => {
-  try {
-    await trpc.category.delete.mutate({ id: category.id });
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
-  }
-};
diff --git a/src/routes/(main)/directory/[[id]]/+page.svelte b/src/routes/(main)/directory/[[id]]/+page.svelte
index 3d01ee0..1a0c95a 100644
--- a/src/routes/(main)/directory/[[id]]/+page.svelte
+++ b/src/routes/(main)/directory/[[id]]/+page.svelte
@@ -3,8 +3,8 @@
   import { page } from "$app/state";
   import { FloatingButton } from "#lib/components/atoms/index.js";
   import { TopBar } from "#lib/components/molecules/index.js";
-  import { getDirectoryInfo, type MaybeDirectoryInfo } from "#lib/modules/filesystem/index.js";
-  import { HybridPromise } from "#lib/utils/index.js";
+  import { tryAction } from "#lib/client/toast.svelte.js";
+  import { createDirectory, uploadFile, useDirectory } from "#lib/features/filesystem/index.js";
   import DirectoryCreateModal from "./DirectoryCreateModal.svelte";
   import DirectoryEntries from "./DirectoryEntries";
   import DownloadStatusCard from "./DownloadStatusCard.svelte";
@@ -14,14 +14,7 @@
   import EntryMenuBottomSheet from "./EntryMenuBottomSheet.svelte";
   import EntryRenameModal from "./EntryRenameModal.svelte";
   import UploadStatusCard from "./UploadStatusCard.svelte";
-  import {
-    createContext,
-    requestDirectoryCreation,
-    requestFileUpload,
-    requestEntryRename,
-    requestEntryDeletion,
-    requestFavoriteToggle,
-  } from "./service.svelte";
+  import { createContext, deleteEntry, renameEntry, toggleEntryFavorite } from "./service.svelte";
 
   import IconSearch from "~icons/material-symbols/search";
   import IconAdd from "~icons/material-symbols/add";
@@ -29,7 +22,8 @@
   let { data } = $props();
   let context = createContext();
 
-  let info: MaybeDirectoryInfo | undefined = $state();
+  const directory = useDirectory(() => data.id);
+  let info = $derived(directory.current);
   let fileInput: HTMLInputElement | undefined = $state();
   let duplicatedFile: File | undefined = $state();
   let resolveForDuplicateFileModal: ((res: boolean) => void) | undefined = $state();
@@ -56,46 +50,33 @@
     await goto(`/search${query ? `?${query}` : ""}`);
   };
 
-  const uploadFile = () => {
+  const uploadFiles = () => {
     const files = fileInput?.files;
     if (!files || files.length === 0) return;
 
     for (const file of files) {
-      requestFileUpload(file, data.id, () => {
-        return new Promise((resolve) => {
-          duplicatedFile = file;
-          resolveForDuplicateFileModal = resolve;
-          isDuplicateFileModalOpen = true;
-        });
-      })
-        .then((res) => {
-          if (!res) return;
-          // TODO: FIXME
-          void getDirectoryInfo(data.id);
-        })
-        .catch((e: Error) => {
-          // TODO: FIXME
-          console.error(e);
-        });
+      void tryAction(
+        () =>
+          uploadFile(file, data.id, () => {
+            return new Promise((resolve) => {
+              duplicatedFile = file;
+              resolveForDuplicateFileModal = resolve;
+              isDuplicateFileModalOpen = true;
+            });
+          }),
+        `'${file.name}' 파일을 업로드하지 못했어요.`,
+      );
     }
 
     fileInput!.value = "";
   };
-
-  $effect(() => {
-    HybridPromise.resolve(getDirectoryInfo(data.id)).then((result) => {
-      if (data.id === result.id) {
-        info = result;
-      }
-    });
-  });
 </script>
 
 <svelte:head>
   <title>내 파일</title>
 </svelte:head>
 
-<input bind:this={fileInput} onchange={uploadFile} type="file" multiple class="hidden" />
+<input bind:this={fileInput} onchange={uploadFiles} type="file" multiple class="hidden" />
 
 <div class="flex h-full flex-col">
   <TopBar title={info?.name ?? "내 파일"} {showBackButton} class="shrink-0">
@@ -150,13 +131,8 @@
 />
 <DirectoryCreateModal
   bind:isOpen={isDirectoryCreateModalOpen}
-  onCreateClick={async (name) => {
-    if (await requestDirectoryCreation(name, data.id)) {
-      void getDirectoryInfo(data.id); // TODO: FIXME
-      return true;
-    }
-    return false;
-  }}
+  onCreateClick={(name) =>
+    tryAction(() => createDirectory(data.id, name), "폴더를 만들지 못했어요.")}
 />
 <DuplicateFileModal
   bind:isOpen={isDuplicateFileModalOpen}
@@ -182,29 +158,22 @@
     isEntryDeleteModalOpen = true;
   }}
   onFavoriteClick={async () => {
-    if (await requestFavoriteToggle(context.selectedEntry!)) {
+    if (
+      await tryAction(
+        () => toggleEntryFavorite(context.selectedEntry!),
+        "즐겨찾기를 변경하지 못했어요.",
+      )
+    ) {
       isEntryMenuBottomSheetOpen = false;
-      void getDirectoryInfo(data.id); // TODO: FIXME
     }
   }}
 />
 <EntryRenameModal
   bind:isOpen={isEntryRenameModalOpen}
-  onRenameClick={async (newName: string) => {
-    if (await requestEntryRename(context.selectedEntry!, newName)) {
-      void getDirectoryInfo(data.id); // TODO: FIXME
-      return true;
-    }
-    return false;
-  }}
+  onRenameClick={(newName: string) =>
+    tryAction(() => renameEntry(context.selectedEntry!, newName), "이름을 바꾸지 못했어요.")}
 />
 <EntryDeleteModal
   bind:isOpen={isEntryDeleteModalOpen}
-  onDeleteClick={async () => {
-    if (await requestEntryDeletion(context.selectedEntry!)) {
-      void getDirectoryInfo(data.id); // TODO: FIXME
-      return true;
-    }
-    return false;
-  }}
+  onDeleteClick={() => tryAction(() => deleteEntry(context.selectedEntry!), "삭제하지 못했어요.")}
 />
diff --git a/src/routes/(main)/directory/[[id]]/DirectoryEntries/DirectoryEntries.svelte b/src/routes/(main)/directory/[[id]]/DirectoryEntries/DirectoryEntries.svelte
index e27029d..9f522da 100644
--- a/src/routes/(main)/directory/[[id]]/DirectoryEntries/DirectoryEntries.svelte
+++ b/src/routes/(main)/directory/[[id]]/DirectoryEntries/DirectoryEntries.svelte
@@ -2,7 +2,7 @@
   import { ActionEntryButton, RowVirtualizer } from "#lib/components/atoms/index.js";
   import { DirectoryEntryLabel } from "#lib/components/molecules/index.js";
   import { getUploadingFiles, type LiveFileUploadState } from "#lib/client/transfer/index.js";
-  import type { DirectoryInfo } from "#lib/modules/filesystem/index.js";
+  import type { DirectoryInfo } from "#lib/features/filesystem/index.js";
   import { sortEntries } from "#lib/utils/index.js";
   import File from "./File.svelte";
   import SubDirectory from "./SubDirectory.svelte";
diff --git a/src/routes/(main)/directory/[[id]]/DirectoryEntries/File.svelte b/src/routes/(main)/directory/[[id]]/DirectoryEntries/File.svelte
index 384a703..46f271c 100644
--- a/src/routes/(main)/directory/[[id]]/DirectoryEntries/File.svelte
+++ b/src/routes/(main)/directory/[[id]]/DirectoryEntries/File.svelte
@@ -2,7 +2,7 @@
   import { ActionEntryButton } from "#lib/components/atoms/index.js";
   import { DirectoryEntryLabel } from "#lib/components/molecules/index.js";
   import { getFileThumbnail } from "#lib/client/cache/index.js";
-  import type { SummarizedFileInfo } from "#lib/modules/filesystem/index.js";
+  import type { SummarizedFileInfo } from "#lib/features/filesystem/index.js";
   import { formatDateTime } from "#lib/utils/index.js";
   import type { SelectedEntry } from "../service.svelte";
 
@@ -22,6 +22,7 @@
     callback({
       type: "file",
       id: info.id,
+      parentId: info.parentId,
       dataKey: info.dataKey,
       name: info.name,
       isFavorite: info.isFavorite,
diff --git a/src/routes/(main)/directory/[[id]]/DirectoryEntries/SubDirectory.svelte b/src/routes/(main)/directory/[[id]]/DirectoryEntries/SubDirectory.svelte
index 7f92440..5f5ff0e 100644
--- a/src/routes/(main)/directory/[[id]]/DirectoryEntries/SubDirectory.svelte
+++ b/src/routes/(main)/directory/[[id]]/DirectoryEntries/SubDirectory.svelte
@@ -1,7 +1,7 @@
 <script lang="ts">
   import { ActionEntryButton } from "#lib/components/atoms/index.js";
   import { DirectoryEntryLabel } from "#lib/components/molecules/index.js";
-  import type { SubDirectoryInfo } from "#lib/modules/filesystem/index.js";
+  import type { SubDirectoryInfo } from "#lib/features/filesystem/index.js";
   import type { SelectedEntry } from "../service.svelte";
 
   import IconMoreVert from "~icons/material-symbols/more-vert";
@@ -18,6 +18,7 @@
     callback({
       type: "directory",
       id: info.id,
+      parentId: info.parentId,
       dataKey: info.dataKey,
       name: info.name,
       isFavorite: info.isFavorite,
diff --git a/src/routes/(main)/directory/[[id]]/service.svelte.ts b/src/routes/(main)/directory/[[id]]/service.svelte.ts
index c5bd0e1..e2934e3 100644
--- a/src/routes/(main)/directory/[[id]]/service.svelte.ts
+++ b/src/routes/(main)/directory/[[id]]/service.svelte.ts
@@ -1,19 +1,18 @@
 import { getContext, setContext } from "svelte";
 import {
-  storeFileCache,
-  deleteFileCache,
-  storeFileThumbnailCache,
-  deleteFileThumbnailCache,
-} from "#lib/client/cache/index.js";
-import { keyring } from "#lib/client/keys/index.js";
-import { uploadFile } from "#lib/client/transfer/index.js";
-import type { DataKey } from "#lib/modules/filesystem/index.js";
-import { generateDataKey, wrapDataKey, encryptString } from "#lib/shared/crypto/index.js";
-import { trpc } from "#trpc/client.js";
+  deleteDirectory,
+  deleteFile,
+  renameDirectory,
+  renameFile,
+  setDirectoryFavorite,
+  setFileFavorite,
+  type DataKey,
+} from "#lib/features/filesystem/index.js";
 
 export interface SelectedEntry {
   type: "directory" | "file";
   id: number;
+  parentId: DirectoryId;
   dataKey: DataKey | undefined;
   name: string;
   isFavorite: boolean;
@@ -30,115 +29,26 @@ export const useContext = () => {
   return getContext<ReturnType<typeof createContext>>("context");
 };
 
-export const requestDirectoryCreation = async (name: string, parentId: "root" | number) => {
-  const masterKey = keyring.activeMasterKey;
-  const { dataKey, dataKeyVersion } = await generateDataKey();
-  const nameEncrypted = await encryptString(name, dataKey);
-
-  try {
-    await trpc.directory.create.mutate({
-      parent: parentId,
-      mekVersion: masterKey.version,
-      dek: await wrapDataKey(dataKey, masterKey.key),
-      dekVersion: dataKeyVersion,
-      name: nameEncrypted.ciphertext,
-      nameIv: nameEncrypted.iv,
-    });
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
+export const renameEntry = async (entry: SelectedEntry, newName: string) => {
+  if (entry.type === "directory") {
+    await renameDirectory(entry, newName);
+  } else {
+    await renameFile(entry, newName);
   }
 };
 
-export const requestFileUpload = async (
-  file: File,
-  parentId: "root" | number,
-  onDuplicate: () => Promise<boolean>,
-) => {
-  const res = await uploadFile(file, parentId, onDuplicate);
-  if (!res) return false;
-
-  if (res.fileBuffer) {
-    storeFileCache(res.fileId, res.fileBuffer); // Intended
-  }
-  if (res.thumbnailBuffer) {
-    storeFileThumbnailCache(res.fileId, res.thumbnailBuffer); // Intended
-  }
-
-  return true;
-};
-
-export const requestEntryRename = async (entry: SelectedEntry, newName: string) => {
-  if (!entry.dataKey) {
-    // TODO: Error Handling
-    return false;
-  }
-
-  const newNameEncrypted = await encryptString(newName, entry.dataKey.key);
-
-  try {
-    if (entry.type === "directory") {
-      await trpc.directory.rename.mutate({
-        id: entry.id,
-        dekVersion: entry.dataKey.version,
-        name: newNameEncrypted.ciphertext,
-        nameIv: newNameEncrypted.iv,
-      });
-    } else {
-      await trpc.file.rename.mutate({
-        id: entry.id,
-        dekVersion: entry.dataKey.version,
-        name: newNameEncrypted.ciphertext,
-        nameIv: newNameEncrypted.iv,
-      });
-    }
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
+export const deleteEntry = async (entry: SelectedEntry) => {
+  if (entry.type === "directory") {
+    await deleteDirectory(entry);
+  } else {
+    await deleteFile(entry);
   }
 };
 
-export const requestEntryDeletion = async (entry: SelectedEntry) => {
-  try {
-    if (entry.type === "directory") {
-      const { deletedFiles } = await trpc.directory.delete.mutate({ id: entry.id });
-      await Promise.all(
-        deletedFiles.flatMap((fileId) => [
-          deleteFileCache(fileId),
-          deleteFileThumbnailCache(fileId),
-        ]),
-      );
-    } else {
-      await trpc.file.delete.mutate({ id: entry.id });
-      await Promise.all([deleteFileCache(entry.id), deleteFileThumbnailCache(entry.id)]);
-    }
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
-  }
-};
-
-export const requestFavoriteToggle = async (entry: SelectedEntry) => {
-  try {
-    if (entry.type === "directory") {
-      if (entry.isFavorite) {
-        await trpc.favorites.removeDirectory.mutate({ id: entry.id });
-      } else {
-        await trpc.favorites.addDirectory.mutate({ id: entry.id });
-      }
-    } else {
-      if (entry.isFavorite) {
-        await trpc.favorites.removeFile.mutate({ id: entry.id });
-      } else {
-        await trpc.favorites.addFile.mutate({ id: entry.id });
-      }
-    }
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
+export const toggleEntryFavorite = async (entry: SelectedEntry) => {
+  if (entry.type === "directory") {
+    await setDirectoryFavorite(entry, !entry.isFavorite);
+  } else {
+    await setFileFavorite(entry, !entry.isFavorite);
   }
 };
diff --git a/src/routes/(main)/favorites/+page.svelte b/src/routes/(main)/favorites/+page.svelte
index bf304c4..a219141 100644
--- a/src/routes/(main)/favorites/+page.svelte
+++ b/src/routes/(main)/favorites/+page.svelte
@@ -5,22 +5,30 @@
   import { TopBar } from "#lib/components/molecules/index.js";
   import Directory from "./Directory.svelte";
   import File from "./File.svelte";
-  import { requestFavoriteEntries, requestRemoveFavorite, type FavoriteEntry } from "./service";
+  import { showErrorToast, tryAction } from "#lib/client/toast.svelte.js";
+  import {
+    getFavoriteEntries,
+    removeFavorite,
+    type FavoriteEntry,
+  } from "#lib/features/favorites/index.js";
 
   import IconSearch from "~icons/material-symbols/search";
 
-  let { data } = $props();
-
   let entries: FavoriteEntry[] = $state([]);
   let isLoading = $state(true);
 
   onMount(async () => {
-    entries = await requestFavoriteEntries(data.favorites);
-    isLoading = false;
+    try {
+      entries = await getFavoriteEntries();
+    } catch (e) {
+      showErrorToast(e, "즐겨찾기를 불러오지 못했어요.");
+    } finally {
+      isLoading = false;
+    }
   });
 
   const handleRemove = async (entry: FavoriteEntry) => {
-    if (await requestRemoveFavorite(entry.type, entry.details.id)) {
+    if (await tryAction(() => removeFavorite(entry), "즐겨찾기를 해제하지 못했어요.")) {
       entries = entries.filter(
         (e) => !(e.type === entry.type && e.details.id === entry.details.id),
       );
diff --git a/src/routes/(main)/favorites/+page.ts b/src/routes/(main)/favorites/+page.ts
deleted file mode 100644
index 6c69f44..0000000
--- a/src/routes/(main)/favorites/+page.ts
+++ /dev/null
@@ -1,8 +0,0 @@
-import { trpc } from "#trpc/client.js";
-import type { PageLoad } from "./$types";
-
-export const load: PageLoad = async ({ parent }) => {
-  await parent(); // Wait for the key guard in the root layout
-  const favorites = await trpc.favorites.get.query();
-  return { favorites };
-};
diff --git a/src/routes/(main)/favorites/Directory.svelte b/src/routes/(main)/favorites/Directory.svelte
index 6648def..2ebd51b 100644
--- a/src/routes/(main)/favorites/Directory.svelte
+++ b/src/routes/(main)/favorites/Directory.svelte
@@ -1,7 +1,7 @@
 <script lang="ts">
   import { ActionEntryButton } from "#lib/components/atoms/index.js";
   import { DirectoryEntryLabel } from "#lib/components/molecules/index.js";
-  import type { SubDirectoryInfo } from "#lib/modules/filesystem/index.js";
+  import type { SubDirectoryInfo } from "#lib/features/filesystem/index.js";
 
   import IconClose from "~icons/material-symbols/close";
 
diff --git a/src/routes/(main)/favorites/File.svelte b/src/routes/(main)/favorites/File.svelte
index 943728f..cb4a1e4 100644
--- a/src/routes/(main)/favorites/File.svelte
+++ b/src/routes/(main)/favorites/File.svelte
@@ -2,7 +2,7 @@
   import { ActionEntryButton } from "#lib/components/atoms/index.js";
   import { DirectoryEntryLabel } from "#lib/components/molecules/index.js";
   import { getFileThumbnail } from "#lib/client/cache/index.js";
-  import type { SummarizedFileInfo } from "#lib/modules/filesystem/index.js";
+  import type { SummarizedFileInfo } from "#lib/features/filesystem/index.js";
   import { formatDateTime } from "#lib/utils/index.js";
 
   import IconClose from "~icons/material-symbols/close";
diff --git a/src/routes/(main)/favorites/service.ts b/src/routes/(main)/favorites/service.ts
deleted file mode 100644
index 3046253..0000000
--- a/src/routes/(main)/favorites/service.ts
+++ /dev/null
@@ -1,61 +0,0 @@
-import {
-  getDirectoryInfo,
-  getFileInfo,
-  type SummarizedFileInfo,
-  type SubDirectoryInfo,
-  type LocalDirectoryInfo,
-} from "#lib/modules/filesystem/index.js";
-import { HybridPromise, sortEntries } from "#lib/utils/index.js";
-import { trpc } from "#trpc/client.js";
-import type { RouterOutputs } from "#trpc/router.server.js";
-
-export type FavoriteEntry =
-  | { type: "directory"; name: string; details: SubDirectoryInfo }
-  | { type: "file"; name: string; details: SummarizedFileInfo };
-
-export const requestFavoriteEntries = async (favorites: RouterOutputs["favorites"]["get"]) => {
-  const [directories, files] = await HybridPromise.all([
-    HybridPromise.all(
-      favorites.directories.map((directory) =>
-        getDirectoryInfo(directory.id, {
-          serverResponse: { ...directory, isFavorite: true },
-        }),
-      ),
-    ),
-    HybridPromise.all(
-      favorites.files.map((file) =>
-        getFileInfo(file.id, { serverResponse: { ...file, isFavorite: true } }),
-      ),
-    ),
-  ]);
-  return [
-    ...sortEntries(
-      directories.map((directory): FavoriteEntry => ({
-        type: "directory",
-        name: directory.name!,
-        details: directory as LocalDirectoryInfo,
-      })),
-    ),
-    ...sortEntries(
-      files.map((file): FavoriteEntry => ({
-        type: "file",
-        name: file.name!,
-        details: file as SummarizedFileInfo,
-      })),
-    ),
-  ];
-};
-
-export const requestRemoveFavorite = async (type: "file" | "directory", id: number) => {
-  try {
-    if (type === "directory") {
-      await trpc.favorites.removeDirectory.mutate({ id });
-    } else {
-      await trpc.favorites.removeFile.mutate({ id });
-    }
-    return true;
-  } catch {
-    // TODO: Error Handling
-    return false;
-  }
-};
diff --git a/src/routes/(main)/home/+page.svelte b/src/routes/(main)/home/+page.svelte
index ff83c69..b441377 100644
--- a/src/routes/(main)/home/+page.svelte
+++ b/src/routes/(main)/home/+page.svelte
@@ -2,7 +2,7 @@
   import { onMount } from "svelte";
   import { goto } from "$app/navigation";
   import { EntryButton, FileThumbnailButton } from "#lib/components/atoms/index.js";
-  import { type SummarizedFileInfo } from "#lib/modules/filesystem/index.js";
+  import { type SummarizedFileInfo } from "#lib/features/filesystem/index.js";
   import { requestFreshMediaFilesRetrieval } from "./service";
 
   let mediaFiles: SummarizedFileInfo[] = $state([]);
diff --git a/src/routes/(main)/menu/+page.svelte b/src/routes/(main)/menu/+page.svelte
index 40f4a26..ace7d69 100644
--- a/src/routes/(main)/menu/+page.svelte
+++ b/src/routes/(main)/menu/+page.svelte
@@ -1,7 +1,8 @@
 <script lang="ts">
   import { goto } from "$app/navigation";
   import MenuEntryButton from "./MenuEntryButton.svelte";
-  import { requestLogout } from "./service";
+  import { tryAction } from "#lib/client/toast.svelte.js";
+  import { logout as requestLogout } from "#lib/features/auth/index.js";
 
   import IconStorage from "~icons/material-symbols/storage";
   import IconImage from "~icons/material-symbols/image";
@@ -11,7 +12,7 @@
   let { data } = $props();
 
   const logout = async () => {
-    if (await requestLogout()) {
+    if (await tryAction(requestLogout, "로그아웃하지 못했어요.")) {
       await goto("/auth/login");
     }
   };
diff --git a/src/routes/(main)/menu/service.ts b/src/routes/(main)/menu/service.ts
deleted file mode 100644
index 04a0e58..0000000
--- a/src/routes/(main)/menu/service.ts
+++ /dev/null
@@ -1 +0,0 @@
-export { requestLogout } from "#lib/services/auth.js";
diff --git a/src/routes/+layout.svelte b/src/routes/+layout.svelte
index e04e0ea..5777c83 100644
--- a/src/routes/+layout.svelte
+++ b/src/routes/+layout.svelte
@@ -1,5 +1,6 @@
 <script lang="ts">
   import { getDownloadingFiles, getUploadingFiles } from "#lib/client/transfer/index.js";
+  import { Toasts } from "#lib/components/atoms/index.js";
   import "../app.css";
 
   let { children } = $props();
@@ -14,3 +15,5 @@
 <svelte:window onbeforeunload={protectFileUploadAndDownload} />
 
 {@render children()}
+
+<Toasts />
diff --git a/tests/unit/filesystemCache.test.ts b/tests/unit/filesystemCache.test.ts
new file mode 100644
index 0000000..603b77a
--- /dev/null
+++ b/tests/unit/filesystemCache.test.ts
@@ -0,0 +1,92 @@
+import { describe, expect, it, vi } from "vitest";
+import { FilesystemCache } from "#lib/features/filesystem/cache.svelte.js";
+
+interface Entry {
+  id: number;
+  name: string;
+}
+
+const createCache = (options?: {
+  local?: Record<number, string>;
+  server?: Record<number, string>;
+}) => {
+  const local = options?.local ?? {};
+  const server = options?.server ?? {};
+  const fetchFromServer = vi.fn(async (id: number): Promise<Entry> => {
+    if (!(id in server)) throw new Error("Not found");
+    return { id, name: server[id]! };
+  });
+  const cache = new FilesystemCache<number, Entry>({
+    fetchFromIndexedDB: async (id) => (id in local ? { id, name: local[id]! } : undefined),
+    fetchFromServer,
+    bulkFetchFromIndexedDB: async (ids) =>
+      new Map([...ids].filter((id) => id in local).map((id) => [id, { id, name: local[id]! }])),
+    bulkFetchFromServer: async (ids) =>
+      new Map([...ids.keys()].map((id) => [id, { id, name: server[id]! }])),
+  });
+  return { cache, server, fetchFromServer };
+};
+
+const flush = () => new Promise((resolve) => setTimeout(resolve, 0));
+
+describe("FilesystemCache", () => {
+  it("resolves with the local value first and updates it in place", async () => {
+    const { cache } = createCache({ local: { 1: "local" }, server: { 1: "server" } });
+
+    const entry = await cache.get(1);
+    expect(entry.name).toBe("local");
+
+    await flush();
+    expect(entry.name).toBe("server");
+  });
+
+  it("returns the cached value synchronously", async () => {
+    const { cache } = createCache({ server: { 1: "server" } });
+
+    const entry = await cache.get(1);
+    await flush();
+
+    expect(cache.get(1)).toBe(entry);
+  });
+
+  it("revalidates entries when invalidated", async () => {
+    const { cache, server, fetchFromServer } = createCache({ server: { 1: "old" } });
+    const entry = await cache.get(1);
+    await flush();
+
+    server[1] = "new";
+    cache.invalidate(1);
+    await flush();
+
+    expect(fetchFromServer).toHaveBeenCalledTimes(2);
+    expect(entry.name).toBe("new");
+  });
+
+  it("ignores invalidation of entries that haven't been loaded", () => {
+    const { cache, fetchFromServer } = createCache();
+
+    cache.invalidate(1);
+
+    expect(fetchFromServer).not.toHaveBeenCalled();
+  });
+
+  it("rejects if loading fails without a cached value", async () => {
+    const { cache } = createCache();
+    vi.spyOn(console, "error").mockImplementation(() => {});
+
+    await expect(cache.get(1)).rejects.toThrow("Not found");
+    // Can be retried
+    await expect(cache.get(1)).rejects.toThrow("Not found");
+  });
+
+  it("loads multiple entries at once", async () => {
+    const { cache } = createCache({ local: { 1: "local" }, server: { 1: "a", 2: "b" } });
+
+    const entries = await cache.bulkGet(new Set([1, 2]));
+    await flush();
+
+    expect(entries.get(1)?.name).toBe("a");
+    expect(entries.get(2)?.name).toBe("b");
+    expect(cache.get(2)).toBe(entries.get(2));
+  });
+});
diff --git a/vitest.config.ts b/vitest.config.ts
index a627a7c..91ce458 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -3,7 +3,7 @@ import { defineConfig } from "vitest/config";
 
 export default defineConfig({
   // Compiles runes in `.svelte.ts` files
-  plugins: [svelte()],
+  plugins: [svelte({ configFile: false })],
   test: {
     projects: [
       {