H2 (URL half): one canonical youtubeId in urlHelpers

Consolidates the scattered YouTube-URL parsing (the clean, renderer-contained
half of H2):

- Move the complete youtubeId (watch/shorts/embed/live/youtu.be) into
  lib/urlHelpers.ts as the single home.
- thumb.ts, queueStats.ts (sameVideo), and store/downloads.ts (titleFromUrl)
  now import it; the three ad-hoc reimplementations are removed.
- titleFromUrl gains correctness: it previously labeled ANY host with a ?v=
  param as "YouTube video (…)" and missed youtu.be/shorts; it's now host-correct
  and covers every YouTube shape. sameVideo now also dedupes /shorts/ID against
  /watch?v=ID.
- Unit-tested in test/clipboardLink.test.ts (+4 cases, 247 pass).

The formatter half of H2 is deferred to travel with H4: the renderer re-parses
speed/eta strings only because raw numbers aren't carried across the IPC boundary
(H4), and fmtBytes (1024) vs formatSpeed (1000) differ intentionally.

typecheck + 247 tests + eslint + prettier green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CODE-AUDIT.md

@@ -224,7 +224,15 @@ token system + shared primitives (UI/SIMP — high value, larger effort) · i18n
 - [ ] **H1 — Decompose god files.** `SettingsView.tsx` (1104, ~11 cards, ~30 selector subs +
   ~20 useState), `DownloadBar.tsx` (858, ~17 state hooks), `store/downloads.ts` (614).
 - [ ] **H2 — Consolidate scattered utilities.** `youtubeId` ×2; 4 YouTube-URL-parsing variants;
-  byte/speed/eta/duration formatting across 4 modules.
+  byte/speed/eta/duration formatting across 4 modules. *URL half done: one canonical `youtubeId` now
+  lives in [urlHelpers.ts](src/renderer/src/lib/urlHelpers.ts) (the complete watch/shorts/embed/live/
+  youtu.be parse); `thumb.ts`, `queueStats.ts` (`sameVideo`), and `store/downloads.ts` (`titleFromUrl`,
+  which also fixes an old bug where any host with a `?v=` param was mislabeled "YouTube video") all import
+  it — the three ad-hoc reimplementations are gone. Unit-tested in `test/clipboardLink.test.ts` (247 pass).
+  **Formatter half still open** and intentionally deferred to travel with **H4**: the renderer only
+  re-parses `speed`/`eta` strings back to numbers because raw numbers aren't carried across the IPC
+  boundary (that's H4), and `fmtBytes` (1024) vs `formatSpeed` (1000) differ on purpose — so a real
+  merge means solving H4 first, not just extracting a shared module.*
 - [x] **H3 — Fix `probe.ts → download.ts` dependency direction** (`fmtBytes` import); resolves
   with H2's shared formatter.
 - [ ] **H4 — Carry raw numbers across the progress boundary.** `DownloadProgress` ships

src/renderer/src/lib/urlHelpers.ts

@@ -1,3 +1,29 @@
+/**
+ * Pull the video id out of any YouTube watch / shorts / embed / live / youtu.be
+ * URL. Returns null for non-YouTube URLs or anything unparseable, so callers can
+ * cheaply ask "is there a YouTube id derivable from this link?". The single home
+ * for this parse — thumbnails, duplicate detection, and the placeholder title all
+ * use it (H2).
+ */
+export function youtubeId(url: string | undefined): string | null {
+  if (!url) return null
+  let u: URL
+  try {
+    u = new URL(url)
+  } catch {
+    return null
+  }
+  const host = u.hostname.replace(/^www\./i, '').toLowerCase()
+  if (host === 'youtu.be') return u.pathname.slice(1).split('/')[0] || null
+  if (host === 'youtube.com' || host.endsWith('.youtube.com')) {
+    const v = u.searchParams.get('v')
+    if (v) return v
+    const m = u.pathname.match(/^\/(?:embed|shorts|v|live)\/([^/?#]+)/i)
+    if (m?.[1]) return m[1]
+  }
+  return null
+}
+
 /** A quick heuristic for "this clipboard text is a link worth offering". */
 export function looksLikeUrl(text: string): boolean {
   const t = text.trim()

src/renderer/src/store/downloads.ts

@@ -11,6 +11,7 @@ import { useSettings } from './settings'
 import { useHistory } from './history'
 import { emit, on } from './coordinator'
 import { newId } from '../id'
+import { youtubeId } from '../lib/urlHelpers'
 
 // Single-sourced from the IPC contract (L105) and re-exported so existing
 // `import { MediaKind } from '../store/downloads'` sites keep working.
@@ -174,11 +175,11 @@ function buildItem(url: string, kind: MediaKind, quality: string, opts?: AddOpti
 }
 
 function titleFromUrl(url: string): string {
+  const id = youtubeId(url)
+  if (id) return `YouTube video (${id})`
   try {
-    const u = new URL(url)
-    const v = u.searchParams.get('v')
-    if (v) return `YouTube video (${v})`
-    if (u.hostname) return `${u.hostname} download`
+    const host = new URL(url).hostname
+    if (host) return `${host} download`
   } catch {
     /* not a URL */
   }

src/renderer/src/store/queueStats.ts

@@ -5,6 +5,7 @@
  * unit-tested without constructing the Zustand store or its preview ticker.
  */
 import type { DownloadItem } from './downloads'
+import { youtubeId } from '../lib/urlHelpers'
 
 // Parse a human speed string ('4.7 MB/s', '512 KiB/s') into bytes/second. Tolerant
 // of the SI (KB) and binary (KiB) suffixes yt-dlp may emit; the 1000-vs-1024
@@ -107,18 +108,6 @@ export function summarizeQueue(items: DownloadItem[]): QueueSummary {
 
 // --- Duplicate detection ----------------------------------------------------
 
-function youtubeId(url: string): string | null {
-  try {
-    const u = new URL(url)
-    const host = u.hostname.replace(/^www\./, '')
-    if (host === 'youtu.be') return u.pathname.slice(1) || null
-    if (host.endsWith('youtube.com')) return u.searchParams.get('v')
-  } catch {
-    /* not a URL */
-  }
-  return null
-}
-
 function normalizeUrl(url: string): string {
   try {
     const u = new URL(url)

src/renderer/src/thumb.ts

@@ -4,30 +4,7 @@
  * video id with no extra network probe. Anything non-YouTube without a probed
  * thumbnail returns undefined, and the UI falls back to a kind icon.
  */
-
-/**
- * Pull the video id out of any YouTube watch / shorts / embed / live / youtu.be
- * URL. Returns null for non-YouTube URLs or anything unparseable, so callers can
- * cheaply ask "is there a thumbnail derivable from this link?".
- */
-export function youtubeId(url: string | undefined): string | null {
-  if (!url) return null
-  let u: URL
-  try {
-    u = new URL(url)
-  } catch {
-    return null
-  }
-  const host = u.hostname.replace(/^www\./i, '').toLowerCase()
-  if (host === 'youtu.be') return u.pathname.slice(1).split('/')[0] || null
-  if (host === 'youtube.com' || host.endsWith('.youtube.com')) {
-    const v = u.searchParams.get('v')
-    if (v) return v
-    const m = u.pathname.match(/^\/(?:embed|shorts|v|live)\/([^/?#]+)/i)
-    if (m?.[1]) return m[1]
-  }
-  return null
-}
+import { youtubeId } from './lib/urlHelpers'
 
 /**
  * Resolve a preview thumbnail URL for a media item. Prefers an explicit thumbnail

test/clipboardLink.test.ts

@@ -1,6 +1,35 @@
 import { describe, it, expect } from 'vitest'
 // Import from the pure utility module directly — no Zustand store init needed (L40).
-import { looksLikeUrl, looksLikeSingleVideo } from '../src/renderer/src/lib/urlHelpers'
+import { looksLikeUrl, looksLikeSingleVideo, youtubeId } from '../src/renderer/src/lib/urlHelpers'
+
+describe('youtubeId', () => {
+  it('extracts the id from a watch URL', () => {
+    expect(youtubeId('https://www.youtube.com/watch?v=dQw4w9WgXcQ')).toBe('dQw4w9WgXcQ')
+    expect(youtubeId('https://youtube.com/watch?v=abc123&list=xyz')).toBe('abc123')
+    expect(youtubeId('https://music.youtube.com/watch?v=musicId')).toBe('musicId')
+  })
+
+  it('extracts the id from a youtu.be short link', () => {
+    expect(youtubeId('https://youtu.be/dQw4w9WgXcQ')).toBe('dQw4w9WgXcQ')
+    expect(youtubeId('https://youtu.be/abc123?t=42')).toBe('abc123')
+  })
+
+  it('extracts the id from shorts / embed / live / v paths', () => {
+    expect(youtubeId('https://www.youtube.com/shorts/shortId1')).toBe('shortId1')
+    expect(youtubeId('https://youtube.com/embed/embedId2')).toBe('embedId2')
+    expect(youtubeId('https://www.youtube.com/live/liveId3')).toBe('liveId3')
+    expect(youtubeId('https://youtube.com/v/vId4?fs=1')).toBe('vId4')
+  })
+
+  it('returns null for non-YouTube, unparseable, or empty input', () => {
+    expect(youtubeId('https://vimeo.com/12345')).toBeNull()
+    expect(youtubeId('https://notyoutube.com/watch?v=x')).toBeNull()
+    expect(youtubeId('https://www.youtube.com/@somechannel')).toBeNull()
+    expect(youtubeId('not a url')).toBeNull()
+    expect(youtubeId(undefined)).toBeNull()
+    expect(youtubeId('')).toBeNull()
+  })
+})
 
 describe('looksLikeUrl', () => {
   it('accepts http(s) URLs', () => {