feat: the extension adds Discord channels to an artist you pick, and its tests gate the XPI (milestone 429)

Server (#4420)
- extension_service gains a Discord pattern (server or channel, jump links,
  ptb/canary; not DMs or threads), mirrored in platforms.js and pinned by
  the shared artist-url-samples.json.
- probe on a Discord URL matches the source by ids under any artist, reports
  a whole-server source as covering the channel, suggests the artist who owns
  another source on the same server, and names server/channel via the stored
  token (best-effort, bounded, no rate-limit waits).
- quick-add takes artist_id / artist_name; Discord URLs are stored canonical.

Extension (#4421, #4422)
- Content script on discord.com; SPA navigation by URL polling (the old
  pushState patch ran in the isolated world and never fired); stale probes
  are dropped.
- Discord chip opens an Add panel: this channel or the whole server, and the
  suggested artist / a search / a new name.
- Popup: sources show artist, platform and state; a Discord token export is
  verified by FC and the result shown. Token capture covers ptb/canary.
- Pure logic in lib/chip.js and lib/popup-format.js, with specs.

CI (#4423)
- extension.yml's lane (web-ext lint, vitest, XPI contents) moves into
  build.yml as extension-test and joins the needs of sign-extension,
  build-web and build-agent. As a separate workflow it gated nothing: a red
  extension suite still signed and shipped the XPI (rule 177).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

extension/test/platforms.spec.js

@@ -7,10 +7,14 @@ import { loadLib } from './helpers/loadLib.js'
 const EXT_DIR = path.join(path.dirname(fileURLToPath(import.meta.url)), '..')
 const manifest = JSON.parse(readFileSync(path.join(EXT_DIR, 'manifest.json'), 'utf8'))
 
-const { getPlatformFromUrl, isArtistPage, PLATFORMS, PLATFORM_ARTIST_PATTERNS } = loadLib(
-  'platforms.js',
-  ['getPlatformFromUrl', 'isArtistPage', 'PLATFORMS', 'PLATFORM_ARTIST_PATTERNS']
-)
+const { getPlatformFromUrl, isArtistPage, parseDiscordUrl, PLATFORMS, PLATFORM_ARTIST_PATTERNS } =
+  loadLib('platforms.js', [
+    'getPlatformFromUrl',
+    'isArtistPage',
+    'parseDiscordUrl',
+    'PLATFORMS',
+    'PLATFORM_ARTIST_PATTERNS'
+  ])
 
 describe('getPlatformFromUrl', () => {
   it('identifies each platform from a domain URL', () => {
@@ -88,8 +92,11 @@ describe('isArtistPage', () => {
     )
   })
 
-  it('returns false for a platform with no artist pattern (discord)', () => {
+  it('matches Discord server and channel pages, not DMs (milestone 429)', () => {
+    expect(isArtistPage('https://discord.com/channels/111/222', 'discord')).toBe(true)
+    expect(isArtistPage('https://discord.com/channels/111', 'discord')).toBe(true)
     expect(isArtistPage('https://discord.com/channels/@me', 'discord')).toBe(false)
+    expect(isArtistPage('https://discord.com/channels/@me/222', 'discord')).toBe(false)
   })
 
   it('returns false for an unknown platform key', () => {
@@ -100,8 +107,8 @@ describe('isArtistPage', () => {
 describe('platform table integrity', () => {
   it('gives every artist pattern a corresponding platform entry', () => {
     // A pattern keyed to a platform that no longer exists is dead code that
-    // silently never fires; the reverse (a platform with no pattern) is the
-    // legitimate discord case, so only this direction is an error.
+    // silently never fires; the reverse (a platform with no pattern) would be
+    // a platform the button never offers, a product choice rather than an error.
     for (const key of Object.keys(PLATFORM_ARTIST_PATTERNS)) {
       expect(Object.keys(PLATFORMS)).toContain(key)
     }
@@ -125,7 +132,8 @@ describe('platform table integrity', () => {
     const samples = {
       patreon: 'https://www.patreon.com/cw/Atole',
       subscribestar: 'https://subscribestar.adult/someone',
-      hentaifoundry: 'https://www.hentai-foundry.com/user/someone'
+      hentaifoundry: 'https://www.hentai-foundry.com/user/someone',
+      discord: 'https://ptb.discord.com/channels/111/222'
     }
     for (const [key, url] of Object.entries(samples)) {
       expect(isArtistPage(url, key), `${key} artist pattern`).toBe(true)
@@ -152,7 +160,7 @@ describe('manifest.json agrees with the platform table', () => {
       )
       expect(owner, `no platform claims content-script match "${m}"`).toBeTruthy()
       // The content script exists to draw the Add-as-source button, so a
-      // platform with no artist pattern (discord) has no business here.
+      // platform with no artist pattern has no business here.
       expect(
         PLATFORM_ARTIST_PATTERNS[owner[0]],
         `"${m}" injects for ${owner[0]}, which has no artist pattern`
@@ -232,9 +240,8 @@ describe('the JS<->Py artist-pattern mirror (#3093)', () => {
 
   it('has samples for every platform that has an artist pattern', () => {
     // The guard's own coverage check: without it, deleting a platform's
-    // samples would make this block pass by testing less. Discord is
-    // deliberately in neither — it is channel-based, with no creator page to
-    // put a button on, so it has no artist pattern on either side.
+    // samples would make this block pass by testing less. Discord joined at
+    // milestone 429 — its slug is server/channel and the artist is chosen.
     expect(Object.keys(samples).sort()).toEqual(Object.keys(PLATFORM_ARTIST_PATTERNS).sort())
   })
 
@@ -247,3 +254,26 @@ describe('the JS<->Py artist-pattern mirror (#3093)', () => {
     }
   })
 })
+
+describe('parseDiscordUrl', () => {
+  it('reads the server and channel ids the Add panel offers', () => {
+    expect(parseDiscordUrl('https://discord.com/channels/111/222')).toEqual({
+      serverId: '111',
+      channelId: '222'
+    })
+    expect(parseDiscordUrl('https://discord.com/channels/111/222/333')).toEqual({
+      serverId: '111',
+      channelId: '222'
+    })
+    expect(parseDiscordUrl('https://discord.com/channels/111')).toEqual({
+      serverId: '111',
+      channelId: null
+    })
+  })
+
+  it('returns null for anything the artist pattern rejects', () => {
+    expect(parseDiscordUrl('https://discord.com/channels/@me/222')).toBe(null)
+    expect(parseDiscordUrl('https://discord.com/app')).toBe(null)
+    expect(parseDiscordUrl('')).toBe(null)
+  })
+})