quak backup works on up to the content pool's limit of originals at once (closes #182)

The backup awaited each original before starting the next, so it used
one of the content pool's five slots. lib.backup(), and so quak backup,
now runs as many workers as the content pool's limit (5 by default, or
the contentConcurrency of the pools the library was opened with), each
taking the next file from one shared list, so the limit covers the
--verify hashing too. Once a worker has thrown or the lock is lost, no
worker takes another file; the backup waits for the files under way and
checks its lock before the ML data fetch. runBackup rejects a
contentConcurrency that is not a positive integer before it takes the
lock. Failed files are listed in the order they failed.

Model: opus-5-5

TODO.md

@@ -32,8 +32,10 @@ declares one.
   the work for one original, its `--verify` hashing included, so no more
   originals than that are open at once. `BackupLibrary` says the limit as
   `contentConcurrency`. A test holds each download at the fake Ente server to
-  count those in flight. Each worker checks the backup's lock before it takes
-  the next file, so once the lock is lost no further original starts.
+  count those in flight. Once a worker has thrown, as one does when `onProgress`
+  throws, or the lock is lost, no worker takes another file; the backup fails
+  once the originals under way are in place, and a lost lock stops it before it
+  fetches ML data.
 
 - 2026-10-14: Next Step said the cache design, issue 36, waits on sneak's
   review, though that issue closed on 2026-10-03 (issue 194). It now names the

src/backup.ts

@@ -730,16 +730,24 @@ const runLockedBackup = async (
     // Up to the content pool's limit of originals are worked on at once,
     // their `verify` hashing included, so however large the account is, no
     // more than that many are open. Each worker takes the next file from the
-    // iterator they all share until none is left, and throws instead once the
-    // lock is lost. A worker that throws, as one also does when `onProgress`
-    // throws, fails the backup only once every worker has stopped, so none
-    // writes into the backup after it has ended.
+    // iterator they all share until none is left. Once a worker has thrown,
+    // as one does when `onProgress` throws, or the lock is lost, no worker
+    // takes another file. The backup fails only once every worker has
+    // stopped, so none writes into the backup after it has ended. It checks
+    // the lock then too, so it does not go on to the thumbnails or the ML
+    // data fetch without it.
     if (includeOriginals) {
         const pending = distinct.values();
+        let workerThrew = false;
         const worker = async (): Promise<void> => {
             for (const file of pending) {
-                if (lock.lost) throw lock.lost;
-                await storeOriginal(file);
+                if (workerThrew || lock.lost) return;
+                try {
+                    await storeOriginal(file);
+                } catch (err) {
+                    workerThrew = true;
+                    throw err;
+                }
             }
         };
         const workers = await Promise.allSettled(
@@ -748,6 +756,7 @@ const runLockedBackup = async (
         for (const w of workers) {
             if (w.status === "rejected") throw w.reason;
         }
+        if (lock.lost) throw lock.lost;
     }
 
     if (includeThumbnails) {

test/cli/backup-end-to-end.test.ts

@@ -704,8 +704,8 @@ describe("a backup whose lock is lost", () => {
         }
     };
 
-    // The backup downloads up to five originals at once, so all three are
-    // under way when the lock is lost, and beach.jpg is stored. The backup
+    // The backup downloads up to five originals at once, so it has started
+    // all three when the lock is lost, and beach.jpg is stored. The backup
     // then stops before it fetches ML data. `quak backup` prints why as one
     // line, with no stack trace, and exits 1.
     it("stops quak backup before it fetches ML data when backup.lock is removed, and exits 1", async () => {