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>

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