quak files COLLECTION fetches that collection's files alone (closes #217)

`quak files COLLECTION` used to wait for a full refresh, which on an
empty cache fetched the files of every collection before it listed one.
It now reads the collection list, then calls the new
`Library.refreshCollection()`, which brings that one collection up to
date in the store as a refresh would, and saves it. It sends no request
for the files when the stored copy is current, and it keeps a newer copy
that a refresh stores while it fetches. It leaves the refresh cursor
alone, so the next refresh still fetches every other collection that
changed. `quak files` with no argument still waits for a refresh.

Model: opus-5-5

README.md

@@ -685,17 +685,20 @@ library. The read commands — `collections`, `files`, `get`, `get-thumb`,
 `helper fix-missing-thumbnails` — force a fresh server round-trip before they
 answer, so they report current account state rather than whatever the cache last
 held. `collections` asks the server for the collection list alone, in one
-request, and neither fetches any collection's files nor changes the cache. The
-others wait for a refresh. With an empty cache, as on a first run, that refresh
-fetches the files of every collection, one collection after another, and stores
-nothing until it has them all, which on a large account takes a while. Meanwhile
-the command logs a line on stderr for each collection whose files it has
-fetched, such as `Fetched the files of 3 of 120 collections`, with `--json` too;
-`backup` does the same while the refresh it starts with runs. stdout holds only
-the command's output. If that round-trip fails, the command prints the error on
-one line and exits 1, or 3 when the server no longer accepts the saved session
-(see "Session handling"). An album or file quak cannot decrypt does not fail it;
-the command answers from what did decrypt (see "Default reads vs. fresh reads").
+request, and neither fetches any collection's files nor changes the cache.
+`files` with a collection ID asks for the collection list the same way, then for
+the files of that collection alone, and stores them in the cache. It asks for
+none of them when the cache's copy of that collection is current. The others
+wait for a refresh. With an empty cache, as on a first run, that refresh fetches
+the files of every collection, one collection after another, and stores nothing
+until it has them all, which on a large account takes a while. Meanwhile the
+command logs a line on stderr for each collection whose files it has fetched,
+such as `Fetched the files of 3 of 120 collections`, with `--json` too; `backup`
+does the same while the refresh it starts with runs. stdout holds only the
+command's output. If that round-trip fails, the command prints the error on one
+line and exits 1, or 3 when the server no longer accepts the saved session (see
+"Session handling"). An album or file quak cannot decrypt does not fail it; the
+command answers from what did decrypt (see "Default reads vs. fresh reads").
 `--cache-dir` overrides where the cache lives; without it each account gets its
 own directory under the per-user cache path.
 
@@ -1180,6 +1183,15 @@ since the stored copy, so a collection stored without its files would never get
 them. `quak collections` uses it (issue
 https://git.eeqj.de/sneak/quak/issues/210).
 
+`await lib.refreshCollection(collection)` brings one collection up to date in
+the cache, given its `Collection` from `freshCollections()`. It does for that
+collection what a refresh does for a changed one, and fetches no other
+collection's files. It sends no request when the cache's copy has the same
+`updationTime`. Otherwise it fetches the collection's files changed since that
+copy, or all of them when there is none, then stores and saves them. The refresh
+cursor stays where it was, so the next refresh still fetches the files of every
+other collection that changed. `quak files` with a collection ID uses it.
+
 An album or file in the server's answer that quak cannot decrypt, or whose
 metadata is not JSON, does not fail the refresh. The refresh leaves it out, an
 album with all its files, and drops any older copy the cache held, so reads

TODO.md

@@ -26,6 +26,15 @@ declares one.
 
 # Completed Steps
 
+- 2026-10-25: `quak files COLLECTION` fetches the files of that collection alone
+  (https://git.eeqj.de/sneak/quak/issues/217). It used to wait for a refresh,
+  which on an empty cache fetched the files of every collection first. It now
+  reads the collection list through `lib.freshCollections()`, then brings that
+  one collection up to date through the new `lib.refreshCollection()`. That
+  stores and saves its files as a refresh would, and leaves the refresh cursor
+  where it was. When the stored copy is current, it asks for none of the files.
+  `quak files` with no argument still waits for a refresh.
+
 - 2026-10-22: The JSON `quak backup` and `quak backup-metadata` write for a file
   holds `keywords` in place of the CLIP embedding in its ML data
   (https://git.eeqj.de/sneak/quak/issues/218). The keywords are the titles of

src/cli-commands.ts

@@ -131,9 +131,10 @@ const readLibraryClient = (client: Client): LibraryClient => ({
 // Open a library for a single point command: the aggressive background precache
 // (issue #48) is off — a one-shot `collections` or `get` must not start
 // downloading the whole account — and no refresh starts as it opens or on a
-// timer: each command asks for the one it needs, and `collections` needs none
-// (issue #210). While a refresh runs, each collection whose files it has
-// fetched is logged, so a large account shows progress rather than nothing.
+// timer: each command asks for the one it needs, and `collections` and
+// `files COLLECTION` need none (issues #210 and #217). While a refresh runs,
+// each collection whose files it has fetched is logged, so a large account
+// shows progress rather than nothing.
 const openReadLibrary = (ctx: CliContext, client: Client): Promise<Library> =>
     Library.open({
         client: readLibraryClient(client),

src/cli-read.ts

@@ -2,13 +2,17 @@
 //
 // `collections`, `files`, `get`, and `get-thumb` must answer for
 // the account's state at the moment the command runs, not for whatever the
-// local cache last happened to hold (owner amendment, issue #36). `files`,
-// `get` and `get-thumb` therefore force a server round-trip through
-// `Library.fresh()` and only then read — so a collection, file, or metadata
-// change made elsewhere is visible. `collections` asks the library for the
-// collection list alone through `Library.freshCollections()` (issue #210): a
-// refresh would also fetch the files of every collection, which on a large
-// account takes long and which `collections` does not print.
+// local cache last happened to hold (owner amendment, issue #36). `files`
+// without a collection ID, `get` and `get-thumb` therefore force a server
+// round-trip through `Library.fresh()` and only then read — so a collection,
+// file, or metadata change made elsewhere is visible. `collections` asks the
+// library for the collection list alone through `Library.freshCollections()`
+// (issue #210): a refresh would also fetch the files of every collection, which
+// on a large account takes long and which `collections` does not print. For the
+// same reason, `files COLLECTION` reads the collection list the same way and
+// then brings that one collection up to date through
+// `Library.refreshCollection()` (issue #217), fetching no other collection's
+// files.
 //
 // `collections` lists in the server's order and `files` in the library's own
 // enumeration order (`listFiles()`), the orders the pre-library CLI printed,
@@ -24,12 +28,12 @@ import type { Photo, PhotosAPI } from "./library/index.js";
 
 // The slice of `Library` these helpers read. `Library` satisfies it
 // structurally; a test can drive them with a stand-in that records the
-// `fresh()` and `freshCollections()` calls and serves records in a known
-// enumeration order.
+// `fresh()`, `freshCollections()` and `refreshCollection()` calls and serves
+// records in a known enumeration order.
 export interface FreshReadLibrary {
     fresh(): Promise<unknown>;
     freshCollections(): Promise<Collection[]>;
-    getCollection(id: number): Collection | undefined;
+    refreshCollection(collection: Collection): Promise<void>;
     listCollections(): Collection[];
     listFiles(collectionID: number): EnteFile[];
     getFileByID(fileID: number): EnteFile | undefined;
@@ -42,21 +46,24 @@ export const freshCollections = (
     lib: FreshReadLibrary,
 ): Promise<Collection[]> => lib.freshCollections();
 
-// The files of one collection, current as of a forced refresh, in enumeration
-// order. `undefined` (not an empty list) when the collection does not exist, so
+// The files of one collection, in enumeration order, current as of one
+// collections request and the requests that bring that collection alone up to
+// date. `undefined` (not an empty list) when the collection does not exist, so
 // the caller can tell "no such collection" from "an empty collection". Without
-// a collection ID, every file in the account, each once, as held by the first
-// collection that holds it.
+// a collection ID, every file in the account, current as of a forced refresh,
+// each once, as held by the first collection that holds it.
 export const freshFiles = async (
     lib: FreshReadLibrary,
     collectionID?: number,
 ): Promise<EnteFile[] | undefined> => {
-    await lib.fresh();
     if (collectionID !== undefined) {
-        return lib.getCollection(collectionID)
-            ? lib.listFiles(collectionID)
-            : undefined;
+        const collections = await lib.freshCollections();
+        const collection = collections.find((c) => c.id === collectionID);
+        if (!collection) return undefined;
+        await lib.refreshCollection(collection);
+        return lib.listFiles(collectionID);
     }
+    await lib.fresh();
     const listed = new Set<number>();
     const files: EnteFile[] = [];
     for (const collection of lib.listCollections()) {

src/library/index.ts

@@ -20,9 +20,12 @@
 //
 // `freshCollections()` is the fresh read of the collection list alone (issue
 // #210): one collections request, no collection's files, and nothing stored,
-// for a caller such as `quak collections` that needs no more. A caller that
-// asks for each refresh it needs can also open the library with
-// `refreshOnOpen: false`, so that `open()` starts none.
+// for a caller such as `quak collections` that needs no more.
+// `refreshCollection()` brings one collection from that list up to date in the
+// store (issue #217): it fetches that collection's files alone, as a refresh
+// would, for a caller such as `quak files COLLECTION`. A caller that asks for
+// each refresh it needs can also open the library with `refreshOnOpen: false`,
+// so that `open()` starts none.
 //
 // A refresh reports through `onProgress` each collection whose files it has
 // fetched, so a large account, whose first refresh fetches the files of every
@@ -625,6 +628,39 @@ export class Library {
         return collections;
     }
 
+    // Bring one collection up to date in the store (issue #217), given its
+    // record from `freshCollections()`. It does for that collection what a
+    // refresh does for a changed one, and fetches no other collection's files.
+    // It sends no request when the stored copy's `updationTime` is as new.
+    // Otherwise it fetches the files changed since the stored copy, or all of
+    // them when none is stored, then commits and saves them. A refresh already
+    // running is waited for first.
+    async refreshCollection(collection: Collection): Promise<void> {
+        if (this.closed) throw new Error("the library is closed");
+        await this.cycle?.catch(() => {});
+        const known = this.store.getCollection(collection.id);
+        if (known && collection.updationTime <= known.updationTime) return;
+        const filePage = await this.client.filesSince({
+            collectionID: collection.id,
+            collectionKey: collection.key,
+            sinceTime: known ? known.updationTime : 0,
+        });
+        // A refresh that ran during the fetch may have stored a copy as new as
+        // `collection` or newer. Committing this result would replace it.
+        const stored = this.store.getCollection(collection.id);
+        if (stored && collection.updationTime <= stored.updationTime) return;
+        // The stored cursor stays where it is, so the next refresh still
+        // fetches the files of every other collection that changed.
+        await this.commit(
+            {
+                collections: [collection],
+                deleted: [],
+                cursor: this.store.collectionsSinceTime,
+            },
+            [{ collectionID: collection.id, page: filePage }],
+        );
+    }
+
     // Back up every in-scope file to `opts.downloadDirectory`, or else the
     // library's, each original at its save path, with a durable failure
     // ledger (issue #51). Takes the lock in that directory first, unless the
@@ -766,10 +802,7 @@ export class Library {
 
     // Fetch every change since the stored cursor, then commit. All network
     // reads happen before any store mutation, so a fetch that throws leaves the
-    // store untouched and the previous snapshot intact. A collection or file
-    // that does not decrypt is left out instead, as if deleted, with the reason
-    // kept in the store: the cursor moves past it, so no later refresh sees it
-    // again until the server's copy changes.
+    // store untouched and the previous snapshot intact.
     private async refreshOnce(): Promise<void> {
         const page = await this.client.collectionsSince({
             sinceTime: this.store.collectionsSinceTime,
@@ -802,6 +835,17 @@ export class Library {
             });
         }
 
+        await this.commit(page, filePages);
+    }
+
+    // Commit a collections page and the file pages fetched for its collections
+    // to the store, then save. A collection or file that does not decrypt is
+    // left out, as if deleted, with the reason kept in the store, and no later
+    // refresh sees it again until the server's copy changes.
+    private async commit(
+        page: CollectionsPage,
+        filePages: { collectionID: number; page: FilesPage }[],
+    ): Promise<void> {
         // Network work done; commit to the store and persist only if something
         // actually changed.
         let changed = false;

test/cli/commands.test.ts

@@ -535,9 +535,7 @@ describe("files", () => {
 
     it("exits 1 for an unknown collection", async () => {
         expect(await filesCommand(context(), "9", {})).toBe(1);
-        expect(stderr.text).toBe(
-            FETCHED_BOTH_ALBUMS + "Collection 9 not found\n",
-        );
+        expect(stderr.text).toBe("Collection 9 not found\n");
     });
 
     // Without a collection ID it lists every file in the account once (issue
@@ -1389,9 +1387,9 @@ describe("backup-metadata --exif", () => {
     });
 });
 
-// Each test first runs `files` so the cache holds the account as it was, then
-// changes the server under it. (`collections` would not do: it reads the
-// collection list alone and stores nothing.)
+// Each test first runs `files 1` so the cache holds Vacation as it was, then
+// adds a file to Vacation on the server. (`collections` would not do: it reads
+// the collection list alone and stores nothing.)
 describe("backup-metadata and the thumbnail helpers refresh first", () => {
     beforeEach(async () => {
         expect(await filesCommand(context(), "1", {})).toBe(0);
@@ -1580,10 +1578,11 @@ describe("an ID given on the command line", () => {
 // An account with many albums (issue #210). On an empty cache `collections`
 // used to wait for a refresh that fetched and decrypted the files of every
 // album, one album after another, before it printed anything, so on such an
-// account it seemed to hang. The account here has 40 albums of one photo each,
-// encrypted as Ente's clients encrypt them, on the fake Ente server of
-// `test/ente-server.ts`, which also records the path of each request quak
-// sends. The session is the one logging in to that server saves.
+// account it seemed to hang. `files` with an album's ID did the same before it
+// listed that album (issue #217). The account here has 40 albums of one photo
+// each, encrypted as Ente's clients encrypt them, on the fake Ente server of
+// `test/ente-server.ts`, which also records the path and query of each request
+// quak sends. The session is the one logging in to that server saves.
 describe("an account with many albums", () => {
     const ALBUMS = 40;
     const PASSWORD = "many-albums";
@@ -1664,7 +1663,8 @@ describe("an account with many albums", () => {
                     : input instanceof URL
                       ? input.href
                       : input.url;
-            paths.push(new URL(url).pathname);
+            const { pathname, search } = new URL(url);
+            paths.push(pathname + search);
             return ente(input, init);
         }) as typeof globalThis.fetch;
         const client = await Client.login({
@@ -1698,7 +1698,7 @@ describe("an account with many albums", () => {
             albums += `${id}\talbum\tAlbum ${id}\n`;
         expect(stdout.text).toBe(albums);
         expect(stderr.text).toBe("");
-        expect(paths).toEqual(["/collections/v2"]);
+        expect(paths).toEqual(["/collections/v2?sinceTime=0"]);
 
         // It stored nothing that would make a refresh skip an album's files:
         // `files` after it still finds the album's photo.
@@ -1707,33 +1707,59 @@ describe("an account with many albums", () => {
         expect(stdout.text).toBe("700\timage\tphoto-7.jpg\n");
     });
 
-    it("files counts on stderr each album whose files its refresh fetched", async () => {
+    it("files fetches the files of the album it lists and of no other", async () => {
         expect(await filesCommand(accountContext(), "7", {})).toBe(0);
 
         expect(stdout.text).toBe("700\timage\tphoto-7.jpg\n");
+        expect(stderr.text).toBe("");
+        expect(paths).toEqual([
+            "/collections/v2?sinceTime=0",
+            "/collections/v2/diff?collectionID=7&sinceTime=0",
+        ]);
+    });
+
+    // The first listing stored the album, so the second finds its stored copy
+    // current and asks for no album's files.
+    it("files run again for the same album sends no request for its files", async () => {
+        const ctx = accountContext();
+        expect(await filesCommand(ctx, "7", {})).toBe(0);
+        stdout.text = "";
+        paths.length = 0;
+
+        expect(await filesCommand(ctx, "7", {})).toBe(0);
+        expect(stdout.text).toBe("700\timage\tphoto-7.jpg\n");
+        expect(paths).toEqual(["/collections/v2?sinceTime=0"]);
+    });
+
+    it("files with no album's ID counts on stderr each album whose files its refresh fetched", async () => {
+        expect(await filesCommand(accountContext(), undefined, {})).toBe(0);
+
+        let photos = "";
         let progress = "";
         for (let n = 1; n <= ALBUMS; n++) {
+            photos += `${n * 100}\timage\tphoto-${n}.jpg\n`;
             progress += `Fetched the files of ${n} of ${ALBUMS} collections\n`;
         }
+        expect(stdout.text).toBe(photos);
         expect(stderr.text).toBe(progress);
     });
 
     // `--json` shapes stdout only, so the refresh's progress is still counted
     // on stderr.
-    it("files --json counts on stderr each album whose files its refresh fetched", async () => {
-        expect(await filesCommand(accountContext(), "7", { json: true })).toBe(
-            0,
-        );
+    it("files --json with no album's ID counts on stderr each album whose files its refresh fetched", async () => {
+        expect(
+            await filesCommand(accountContext(), undefined, { json: true }),
+        ).toBe(0);
 
-        expect(JSON.parse(stdout.text)).toEqual([
-            {
-                id: 700,
-                title: "photo-7.jpg",
-                fileType: "image",
-                creationTime: 1000,
-                collectionID: 7,
-            },
-        ]);
+        const rows = JSON.parse(stdout.text);
+        expect(rows).toHaveLength(ALBUMS);
+        expect(rows[6]).toEqual({
+            id: 700,
+            title: "photo-7.jpg",
+            fileType: "image",
+            creationTime: 1000,
+            collectionID: 7,
+        });
         let progress = "";
         for (let n = 1; n <= ALBUMS; n++) {
             progress += `Fetched the files of ${n} of ${ALBUMS} collections\n`;

test/cli/read.test.ts

@@ -3,13 +3,16 @@
  * issue #36, issue #52).
  *
  * The `collections`, `files`, `get`, and `get-thumb` commands must answer for
- * current server state, not the local cache. `files`, `get` and `get-thumb`
- * force a `Library.fresh()` round-trip before they read; the stand-in library
- * below serves nothing until `fresh()` has been awaited, so a helper that read
- * without refreshing would come back empty and fail here. `collections` asks
- * the library for the collection list alone (`freshCollections()`, issue
- * #210), and must not wait for a refresh, which would fetch the files of every
- * collection.
+ * current server state, not the local cache. `files` without a collection ID,
+ * `get` and `get-thumb` force a `Library.fresh()` round-trip before they read;
+ * the stand-in library below serves nothing until `fresh()` has been awaited,
+ * so a helper that read without refreshing would come back empty and fail
+ * here. `collections` asks the library for the collection list alone
+ * (`freshCollections()`, issue #210), and must not wait for a refresh, which
+ * would fetch the files of every collection. `files COLLECTION` reads that list
+ * too and then brings that one collection up to date
+ * (`refreshCollection()`, issue #217); the stand-in serves a collection's files
+ * once either has run.
  *
  * `collections` and `files` also list in the library's enumeration order
  * (`listCollections`/`listFiles`) — the order the pre-library CLI printed — not
@@ -64,12 +67,14 @@ const file = (
 
 // A library that reveals its records only after `fresh()` has been awaited, and
 // serves them in the enumeration order it was given. `freshCollections()`
-// answers the collection list in that order without a refresh. `photos.byID`
-// returns a stand-in `Photo` carrying just the fileID the helper passes
-// through.
+// answers the collection list in that order without a refresh.
+// `refreshCollection()` reveals the files of that one collection.
+// `photos.byID` returns a stand-in `Photo` carrying just the fileID the helper
+// passes through.
 class FakeLibrary implements FreshReadLibrary {
     freshCalls = 0;
     freshCollectionsCalls = 0;
+    refreshCollectionIDs: number[] = [];
     private refreshed = false;
 
     constructor(
@@ -88,9 +93,8 @@ class FakeLibrary implements FreshReadLibrary {
         return this.collections;
     }
 
-    getCollection(id: number): Collection | undefined {
-        if (!this.refreshed) return undefined;
-        return this.collections.find((c) => c.id === id);
+    async refreshCollection(collection: Collection): Promise<void> {
+        this.refreshCollectionIDs.push(collection.id);
     }
 
     listCollections(): Collection[] {
@@ -98,7 +102,9 @@ class FakeLibrary implements FreshReadLibrary {
     }
 
     listFiles(collectionID: number): EnteFile[] {
-        return this.refreshed
+        const current =
+            this.refreshed || this.refreshCollectionIDs.includes(collectionID);
+        return current
             ? this.files.filter((f) => f.collectionID === collectionID)
             : [];
     }
@@ -138,18 +144,25 @@ describe("CLI read helpers (issue #36 amendment, issue #52)", () => {
         expect(rows.map((c) => c.id)).not.toEqual(newestFirst);
     });
 
-    it("freshFiles refreshes first, lists in enumeration order, keeps raw fields", async () => {
+    it("freshFiles brings the collection alone up to date, lists in enumeration order, keeps raw fields", async () => {
         // Enumeration order by id 10, 11, 12; creationTimes ascending, so a
-        // newest-first sort would reverse them.
+        // newest-first sort would reverse them. Collection 2's file is not
+        // listed.
         const files = [
             file(10, 1, 1_700_000_000_000_000),
             file(11, 1, 1_700_000_000_000_001),
             file(12, 1, 1_700_000_000_000_002),
+            file(20, 2, 1_700_000_000_000_003),
         ];
-        const lib = new FakeLibrary([collection(1, 100)], files);
+        const lib = new FakeLibrary(
+            [collection(1, 100), collection(2, 100)],
+            files,
+        );
 
         const rows = await freshFiles(lib, 1);
-        expect(lib.freshCalls).toBe(1);
+        expect(lib.freshCollectionsCalls).toBe(1);
+        expect(lib.refreshCollectionIDs).toEqual([1]);
+        expect(lib.freshCalls).toBe(0);
         expect(rows?.map((f) => f.id)).toEqual([10, 11, 12]);
 
         // Field values come from raw metadata: microsecond creationTime and the
@@ -206,7 +219,9 @@ describe("CLI read helpers (issue #36 amendment, issue #52)", () => {
     it("freshFiles returns undefined for an unknown collection", async () => {
         const lib = new FakeLibrary([collection(1, 100)], []);
         const rows = await freshFiles(lib, 999);
-        expect(lib.freshCalls).toBe(1);
+        expect(lib.freshCollectionsCalls).toBe(1);
+        expect(lib.refreshCollectionIDs).toEqual([]);
+        expect(lib.freshCalls).toBe(0);
         expect(rows).toBeUndefined();
     });
 

test/library/fresh.test.ts

@@ -17,6 +17,10 @@
  *  4. `freshCollections()` reads the collection list alone, with one request
  *     and no collection's files, and stores nothing, so the next refresh still
  *     fetches the files of every collection (issue #210).
+ *  5. `refreshCollection()` brings one collection up to date in the store and
+ *     leaves the stored cursor where it was, so the next refresh still fetches
+ *     the files of every other collection that changed (issue #217). A newer
+ *     copy that a refresh stores while it fetches the files is kept.
  *
  * The client is the same metadata-only mock the background-refresh tests use:
  * no crypto, no network, scripted pages, and a record of each call. A long
@@ -340,3 +344,132 @@ describe("Library.freshCollections", () => {
         }
     });
 });
+
+describe("Library.refreshCollection", () => {
+    let dir: string;
+    let cacheDirectory: string;
+
+    beforeEach(() => {
+        dir = mkdtempSync(join(tmpdir(), "quak-refresh-collection-"));
+        cacheDirectory = join(dir, "cache");
+    });
+
+    afterEach(() => {
+        rmSync(dir, { recursive: true, force: true });
+    });
+
+    // Collections 1 and 2 are stored at updationTime 100, with a stored cursor
+    // of 100, and then both change on the server.
+    it("fetches the files of one changed collection and leaves the others to the next refresh", async () => {
+        const client = new MockClient();
+        client.collectionsQueue.push({
+            collections: [collection(1, 100), collection(2, 100)],
+            deleted: [],
+            cursor: 100,
+        });
+        client.filesFor(1, {
+            files: [file(1001, 1, 90)],
+            deleted: [],
+            cursor: 90,
+        });
+        client.filesFor(2, {
+            files: [file(2001, 2, 90)],
+            deleted: [],
+            cursor: 90,
+        });
+        const lib = await Library.open({
+            client,
+            cacheDirectory,
+            refreshIntervalSeconds: SLOW_INTERVAL,
+        });
+        try {
+            client.filesCalls.length = 0;
+            client.filesFor(1, {
+                files: [file(1002, 1, 110)],
+                deleted: [],
+                cursor: 110,
+            });
+            client.filesFor(2, {
+                files: [file(2002, 2, 120)],
+                deleted: [],
+                cursor: 120,
+            });
+
+            // Collection 1's files alone, since the stored copy.
+            await lib.refreshCollection(collection(1, 110));
+            expect(client.filesCalls).toEqual([
+                { collectionID: 1, sinceTime: 100 },
+            ]);
+            expect(lib.listFiles(1).map((f) => f.id)).toEqual([1001, 1002]);
+            expect(lib.listFiles(2).map((f) => f.id)).toEqual([2001]);
+
+            // The stored copy is now current, so no request.
+            await lib.refreshCollection(collection(1, 110));
+            expect(client.filesCalls).toHaveLength(1);
+
+            // The next refresh asks from the stored cursor, 100, so it still
+            // sees collection 2 changed and fetches its files.
+            client.collectionsQueue.push({
+                collections: [collection(1, 110), collection(2, 120)],
+                deleted: [],
+                cursor: 120,
+            });
+            await lib.fresh();
+            expect(client.collectionsSinceTimes).toEqual([0, 100]);
+            expect(client.filesCalls).toEqual([
+                { collectionID: 1, sinceTime: 100 },
+                { collectionID: 2, sinceTime: 100 },
+            ]);
+            expect(lib.listFiles(2).map((f) => f.id)).toEqual([2001, 2002]);
+        } finally {
+            await lib.close();
+        }
+    });
+
+    // Collection 1 is stored at 100. `refreshCollection()` asks for it at 110,
+    // which adds file 1002. While that files request waits, a refresh stores
+    // it at 120, where 1002 is deleted again and 1003 added.
+    it("keeps a newer copy that a refresh stores while the files are fetched", async () => {
+        const { client, lib } = await openSeeded(cacheDirectory);
+        let release!: () => void;
+        const held = new Promise<void>((r) => (release = r));
+        try {
+            client.filesFor(
+                1,
+                { files: [file(1002, 1, 110)], deleted: [], cursor: 110 },
+                { files: [file(1003, 1, 120)], deleted: [1002], cursor: 120 },
+            );
+            client.collectionsQueue.push({
+                collections: [collection(1, 120)],
+                deleted: [],
+                cursor: 120,
+            });
+
+            // Hold the next files request, refreshCollection's, until the
+            // test releases it. The refresh's request after it is answered
+            // at once.
+            let fetchStarted!: () => void;
+            const started = new Promise<void>((r) => (fetchStarted = r));
+            const realFilesSince = client.filesSince.bind(client);
+            client.filesSince = async (args) => {
+                client.filesSince = realFilesSince;
+                const page = await realFilesSince(args);
+                fetchStarted();
+                await held;
+                return page;
+            };
+
+            const refreshing = lib.refreshCollection(collection(1, 110));
+            await started;
+            await lib.fresh();
+            release();
+            await refreshing;
+
+            expect(lib.getCollection(1)?.updationTime).toBe(120);
+            expect(lib.listFiles(1).map((f) => f.id)).toEqual([1001, 1003]);
+        } finally {
+            release();
+            await lib.close();
+        }
+    });
+});