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/metadata-backup.test.ts

@@ -47,7 +47,7 @@ import {
     type MetadataBackupOptions,
 } from "../../src/metadata-backup.js";
 import { backupMetadataCommand } from "../../src/cli-commands.js";
-import { stderrLog } from "../../src/cli-log.js";
+import { stderrLog, type LogLevel } from "../../src/cli-log.js";
 import {
     buildAccount,
     buildMetaFetch,
@@ -491,9 +491,12 @@ describe("quak backup-metadata", () => {
 });
 
 describe("quak backup-metadata when a file's ML data cannot be read", () => {
-    // Run the CLI command against `fetch`, the mock unless given, and return
-    // its exit code, stderr and output directory.
-    const runCommand = async (fetch = buildMetaFetch(mock)) => {
+    // Run the CLI command against `fetch`, the mock unless given, logging at
+    // `level`, and return its exit code, stderr and output directory.
+    const runCommand = async (
+        fetch = buildMetaFetch(mock),
+        level: LogLevel = "info",
+    ) => {
         const client = await Client.login({
             email: TEST_EMAIL,
             password: TEST_PASSWORD,
@@ -509,7 +512,7 @@ describe("quak backup-metadata when a file's ML data cannot be read", () => {
                 stdout: { write: () => true },
                 log: stderrLog(
                     { write: (text: string) => (stderr += text) },
-                    "info",
+                    level,
                 ),
                 sessionDir: testDir,
                 cacheDir: mkdtempSync(join(testDir, "cache-")),
@@ -521,13 +524,16 @@ describe("quak backup-metadata when a file's ML data cannot be read", () => {
         return { code, stderr, outDir };
     };
 
+    // The failed request is logged at error, so it is the first line printed
+    // at that level.
     it("writes every file, marks the failed batch's files, and exits 1", async () => {
         const { code, stderr, outDir } = await runCommand(
             buildMetaFetch(mock, 200),
+            "error",
         );
 
         expect(code).toBe(1);
-        expect(stderr).toContain("ML data request for 1 file(s) failed");
+        expect(stderr).toMatch(/^ML data request for 1 file\(s\) failed: /);
 
         const ok = JSON.parse(
             readFileSync(
@@ -550,7 +556,9 @@ describe("quak backup-metadata when a file's ML data cannot be read", () => {
     });
 
     // The server sends ML data for diagram.png encrypted under a key that is
-    // not the file's, so quak cannot decrypt it.
+    // not the file's, so quak cannot decrypt it. That is logged at error, and
+    // the last line is fatal, so `-q`, which prints fatal lines only, still
+    // says why the command exits 1.
     it("writes the reason for ML data that does not decrypt, and exits 1", async () => {
         const otherKey = sodium.crypto_secretstream_xchacha20poly1305_keygen();
         const { header, ciphertext } = encryptBlob(
@@ -568,12 +576,14 @@ describe("quak backup-metadata when a file's ML data cannot be read", () => {
                     },
                 },
             }),
+            "error",
         );
 
         expect(code).toBe(1);
         const reason = "secretstream chunk authentication failed";
-        expect(stderr).toContain(
-            `ML data of file 200 could not be read: ${reason}\n`,
+        expect(stderr).toBe(
+            `ML data of file 200 could not be read: ${reason}\n` +
+                `quak: the ML data of 1 file(s) could not be read; see mlDataError in their JSON in ${outDir}\n`,
         );
         const failed = JSON.parse(
             readFileSync(