feat(audit): Batch 24 — one validate-and-coerce schema layer for settings (CC9)

zod field schemas in settingsSchema.ts replace setSettings' bespoke
per-key switch: parse → skip-on-fail → store, side effects (secret
encryption, launch-at-startup sync) kept in settings.ts. sanitizeOptions
extracted to settingsOptions.ts to break the import cycle; backup import
flows through the same schema. Field-by-field parity pinned in
test/settingsSchema.test.ts (15 tests); full suite unchanged.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/settingsSchema.test.ts

@@ -0,0 +1,110 @@
+/**
+ * CC9: the zod field schemas must be a faithful port of the old setSettings
+ * switch — same accepts, same rejects, same coercions (clamp/trim/sanitize).
+ */
+import { describe, it, expect } from 'vitest'
+import { parseSettingsField } from '../src/main/settingsSchema'
+import { DEFAULT_DOWNLOAD_OPTIONS } from '@shared/ipc'
+
+const ok = <T>(v: T): { ok: true; value: T } => ({ ok: true, value: v })
+const fail = { ok: false }
+
+describe('parseSettingsField (CC9 schema parity)', () => {
+  it('theme: enum only', () => {
+    expect(parseSettingsField('theme', 'dark')).toEqual(ok('dark'))
+    expect(parseSettingsField('theme', 'blue')).toEqual(fail)
+    expect(parseSettingsField('theme', 1)).toEqual(fail)
+  })
+
+  it('maxConcurrent: coerces, rounds, clamps to [1,5]', () => {
+    expect(parseSettingsField('maxConcurrent', 3)).toEqual(ok(3))
+    expect(parseSettingsField('maxConcurrent', '4')).toEqual(ok(4))
+    expect(parseSettingsField('maxConcurrent', 99)).toEqual(ok(5))
+    expect(parseSettingsField('maxConcurrent', -2)).toEqual(ok(1))
+    expect(parseSettingsField('maxConcurrent', 2.6)).toEqual(ok(3))
+    expect(parseSettingsField('maxConcurrent', 'abc')).toEqual(fail)
+  })
+
+  it('aria2cConnections: clamps to [1,16] (L64)', () => {
+    expect(parseSettingsField('aria2cConnections', 64)).toEqual(ok(16))
+    expect(parseSettingsField('aria2cConnections', 0)).toEqual(ok(1))
+  })
+
+  it('syncTime: 24h HH:MM only (L51)', () => {
+    expect(parseSettingsField('syncTime', '09:30')).toEqual(ok('09:30'))
+    expect(parseSettingsField('syncTime', '9:30')).toEqual(fail)
+    expect(parseSettingsField('syncTime', '24:00')).toEqual(fail)
+  })
+
+  it('booleans: strict', () => {
+    expect(parseSettingsField('useAria2c', true)).toEqual(ok(true))
+    expect(parseSettingsField('useAria2c', 'true')).toEqual(fail)
+    expect(parseSettingsField('enableCustomCommands', false)).toEqual(ok(false))
+  })
+
+  it('ytdlpChannel: allowlist (F1)', () => {
+    expect(parseSettingsField('ytdlpChannel', 'nightly')).toEqual(ok('nightly'))
+    expect(parseSettingsField('ytdlpChannel', 'master')).toEqual(fail)
+  })
+
+  it('ytdlpLastUpdateCheck: non-negative finite number, coerced', () => {
+    expect(parseSettingsField('ytdlpLastUpdateCheck', 123)).toEqual(ok(123))
+    expect(parseSettingsField('ytdlpLastUpdateCheck', -1)).toEqual(fail)
+    expect(parseSettingsField('ytdlpLastUpdateCheck', 'NaN')).toEqual(fail)
+  })
+
+  it('defaultTemplateId: string or null', () => {
+    expect(parseSettingsField('defaultTemplateId', null)).toEqual(ok(null))
+    expect(parseSettingsField('defaultTemplateId', 't1')).toEqual(ok('t1'))
+    expect(parseSettingsField('defaultTemplateId', 7)).toEqual(fail)
+  })
+
+  it('downloadOptions: always sanitizes to a full valid object', () => {
+    const r = parseSettingsField('downloadOptions', { embedSubtitles: true, audioFormat: 'nope' })
+    expect(r.ok).toBe(true)
+    if (r.ok) {
+      expect(r.value.embedSubtitles).toBe(true)
+      expect(r.value.audioFormat).toBe(DEFAULT_DOWNLOAD_OPTIONS.audioFormat)
+      expect(Object.keys(r.value).length).toBeGreaterThanOrEqual(
+        Object.keys(DEFAULT_DOWNLOAD_OPTIONS).length - 3 // optional metadata fields may be undefined
+      )
+    }
+  })
+
+  it('folders: trims; empty clears; relative paths rejected (isSafeOutputDir)', () => {
+    expect(parseSettingsField('videoFolder', '  D:\\Media  ')).toEqual(ok('D:\\Media'))
+    expect(parseSettingsField('videoFolder', '')).toEqual(ok(''))
+    expect(parseSettingsField('audioFolder', 'Downloads')).toEqual(fail)
+    expect(parseSettingsField('audioFolder', '..\\elsewhere')).toEqual(fail)
+  })
+
+  it('filenameTemplate: trimmed and safety-checked', () => {
+    expect(parseSettingsField('filenameTemplate', ' %(title)s.%(ext)s ')).toEqual(
+      ok('%(title)s.%(ext)s')
+    )
+    expect(parseSettingsField('filenameTemplate', '../%(title)s.%(ext)s')).toEqual(fail)
+  })
+
+  it('rateLimit: yt-dlp format or empty', () => {
+    expect(parseSettingsField('rateLimit', '2.5M')).toEqual(ok('2.5M'))
+    expect(parseSettingsField('rateLimit', ' 500K ')).toEqual(ok('500K'))
+    expect(parseSettingsField('rateLimit', '')).toEqual(ok(''))
+    expect(parseSettingsField('rateLimit', 'fast')).toEqual(fail)
+  })
+
+  it('quality presets: allowlisted', () => {
+    expect(parseSettingsField('defaultVideoQuality', '720p')).toEqual(ok('720p'))
+    expect(parseSettingsField('defaultVideoQuality', '4K')).toEqual(fail)
+    expect(parseSettingsField('defaultAudioQuality', 'Best')).toEqual(ok('Best'))
+  })
+
+  it('secrets: plain strings pass through (encryption happens in settings.ts)', () => {
+    expect(parseSettingsField('proxy', 'socks5://u:p@h:1')).toEqual(ok('socks5://u:p@h:1'))
+    expect(parseSettingsField('updateToken', ' tok ')).toEqual(ok('tok'))
+    expect(parseSettingsField('proxy', 42)).toEqual(fail)
+  })
+
+  it('unknown keys are skipped', () => {
+    expect(parseSettingsField('nope' as never, true)).toEqual(fail)
+  })
+})