Complete Phase C (custom commands & yt-dlp updater) and Phase D (library, UX & notifications)

Phase C had been implemented in the working tree but never committed:
named custom-command templates (CRUD + per-download override), command
preview, and the in-app yt-dlp self-updater.

Phase D adds: history search/kind-filter/multi-select/bulk-delete/
re-download; native OS notifications on completion/failure; a private/
incognito download mode that skips history; settings+template backup/
restore via JSON; and a persistent error log surfaced as a Diagnostics
report in Settings.

See ROADMAP.md for the full per-item breakdown.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/buildArgs.test.ts

@@ -1,5 +1,12 @@
 import { describe, it, expect } from 'vitest'
-import { buildArgs, CROP_SQUARE_PPA, ARIA2C_ARGS, type AccessOptions } from '../src/main/buildArgs'
+import {
+  buildArgs,
+  parseExtraArgs,
+  formatCommandLine,
+  CROP_SQUARE_PPA,
+  ARIA2C_ARGS,
+  type AccessOptions
+} from '../src/main/buildArgs'
 import {
   DEFAULT_DOWNLOAD_OPTIONS,
   type DownloadOptions,
@@ -25,9 +32,10 @@ function dlo(overrides: Partial<DownloadOptions> = {}): DownloadOptions {
 function build(
   o: StartDownloadOptions,
   d: DownloadOptions,
-  access: AccessOptions = NO_ACCESS
+  access: AccessOptions = NO_ACCESS,
+  extraArgs: string[] = []
 ): string[] {
-  return buildArgs(o, OUT, d, BIN, access)
+  return buildArgs(o, OUT, d, BIN, access, extraArgs)
 }
 
 /** True when `seq` appears as a contiguous run inside `argv`. */
@@ -283,3 +291,72 @@ describe('cropThumbnail → --ppa crop', () => {
     expect(argv).not.toContain('--embed-thumbnail')
   })
 })
+
+// --- Custom commands (Phase C): extra args + display formatting ------------
+
+describe('parseExtraArgs', () => {
+  it('splits on whitespace', () => {
+    expect(parseExtraArgs('--write-thumbnail --no-mtime')).toEqual([
+      '--write-thumbnail',
+      '--no-mtime'
+    ])
+  })
+
+  it('keeps a double-quoted span with spaces as one token', () => {
+    expect(parseExtraArgs('--proxy "http://example.com:8080"')).toEqual([
+      '--proxy',
+      'http://example.com:8080'
+    ])
+  })
+
+  it('keeps a single-quoted span with spaces as one token', () => {
+    expect(parseExtraArgs("--output-na 'My Title - %(id)s.%(ext)s'")).toEqual([
+      '--output-na',
+      'My Title - %(id)s.%(ext)s'
+    ])
+  })
+
+  it('returns an empty array for blank input', () => {
+    expect(parseExtraArgs('')).toEqual([])
+    expect(parseExtraArgs('   ')).toEqual([])
+  })
+
+  it('collapses repeated whitespace between tokens', () => {
+    expect(parseExtraArgs('--verbose    --no-progress')).toEqual(['--verbose', '--no-progress'])
+  })
+})
+
+describe('formatCommandLine', () => {
+  it('joins the exe and args with spaces when nothing needs quoting', () => {
+    expect(formatCommandLine('yt-dlp.exe', ['-f', 'best', '--', 'https://x.test/v'])).toBe(
+      'yt-dlp.exe -f best -- https://x.test/v'
+    )
+  })
+
+  it('quotes an arg containing a space', () => {
+    expect(formatCommandLine('yt-dlp.exe', ['--ppa', 'EmbedThumbnail+ffmpeg_o:-c:v mjpeg'])).toBe(
+      'yt-dlp.exe --ppa "EmbedThumbnail+ffmpeg_o:-c:v mjpeg"'
+    )
+  })
+
+  it('escapes embedded double quotes', () => {
+    expect(formatCommandLine('yt-dlp.exe', ['say "hi"'])).toBe('yt-dlp.exe "say \\"hi\\""')
+  })
+
+  it('renders an empty-string arg as ""', () => {
+    expect(formatCommandLine('yt-dlp.exe', [''])).toBe('yt-dlp.exe ""')
+  })
+})
+
+describe('buildArgs extraArgs', () => {
+  it('appends extraArgs after every other option, still before -- url', () => {
+    const argv = build(opts(), dlo(), NO_ACCESS, ['--write-thumbnail', '--no-mtime'])
+    expect(hasSeq(argv, '--write-thumbnail', '--no-mtime', '--', URL)).toBe(true)
+  })
+
+  it('omits nothing extra when extraArgs is empty', () => {
+    const withEmpty = build(opts(), dlo(), NO_ACCESS, [])
+    const withoutParam = build(opts(), dlo())
+    expect(withEmpty).toEqual(withoutParam)
+  })
+})