Failed runs end with one fatal line; failure lines are errors

A command that exits 1 because files or albums failed now ends with one
fatal line saying how many failed and where to look, so -q never leaves
a non-zero exit unexplained: backup points to failures.json, backup-metadata
to mlDataError in each file's JSON, and fix-missing-thumbnails to its
Failed files list. The progress callbacks of the backup, the metadata
backup and the thumbnail helpers take a level, so every line that reports
a failure is logged at error. The library's operation names are shown in
plain words. The README says which lines are error and warning, and which
summary lines --json replaces.

Model: opus-5-5

test/cli/commands.test.ts

@@ -913,6 +913,38 @@ describe("backup", () => {
         );
     });
 
+    // A failed file is an error line both where the backup fails it and in
+    // the list at the end. The last line is fatal, so `-q`, which prints
+    // fatal lines only, still says why the backup exits 1.
+    it("logs a failed file at error, and ends with one fatal line counting the failures", async () => {
+        const dir = join(root, "backup");
+        const last = `quak: 1 file(s) and 0 album(s) failed; see ${join(dir, "failures.json")} and the FAILED lines\n`;
+        const ctx = context(fakeClient({ failID: 101 }));
+        expect(
+            await backupCommand(
+                { ...ctx, log: stderrLog(stderr, "error") },
+                dir,
+                {},
+            ),
+        ).toBe(1);
+        expect(stderr.text).toBe(
+            "FAILED original sunset.jpg: HTTP 500 from server\n" +
+                "\nFailed files:\n" +
+                "  [Vacation] sunset.jpg (id 101): HTTP 500 from server\n" +
+                last,
+        );
+
+        stderr.text = "";
+        expect(
+            await backupCommand(
+                { ...ctx, log: stderrLog(stderr, "fatal") },
+                dir,
+                { json: true },
+            ),
+        ).toBe(1);
+        expect(stderr.text).toBe(last);
+    });
+
     // `--json` shapes stdout only: the log lines stay on stderr, and the JSON
     // takes the place of the summary.
     it("prints the result as JSON with --json, still exiting 1 on a failure", async () => {
@@ -1303,6 +1335,34 @@ describe("helper list-missing-thumbnails", () => {
     });
 });
 
+describe("helper fix-missing-thumbnails", () => {
+    // File 999 is in no album, so fixing it fails. The list of failed files
+    // is at error, and the last line is fatal, so `-q`, which prints fatal
+    // lines only, still says why the command exits 1.
+    it("lists a failed file at error, and ends with one fatal line counting the failures", async () => {
+        const last = `quak: 1 file(s) failed; see the "Failed files:" list, or the JSON with --json\n`;
+        const ctx = { ...context(), log: stderrLog(stderr, "error") };
+        expect(await fixMissingThumbnailsCommand(ctx, { file: ["999"] })).toBe(
+            1,
+        );
+        expect(stderr.text).toBe(
+            "\nFailed files:\n" +
+                "  999\tunknown\tfile not found in any collection\n" +
+                last,
+        );
+
+        stderr.text = "";
+        const quiet = { ...context(), log: stderrLog(stderr, "fatal") };
+        expect(
+            await fixMissingThumbnailsCommand(quiet, {
+                file: ["999"],
+                json: true,
+            }),
+        ).toBe(1);
+        expect(stderr.text).toBe(last);
+    });
+});
+
 describe("backup-metadata --exif", () => {
     // Runs the command and returns what it printed to stderr.
     const backupMetadata = async (opts: { exif?: boolean; all?: boolean }) => {