feat(v0.8.679): Phase 704 thread archive CSV & forum tag export mesh parity

Complete signed guild thread archive CSV mesh export and forum tag palette
export (RPC 126/127): thread-csv-ui.js, thread-csv-mixin.js, delivery-receipts
store, guild gossip handlers, ui-flow IPC, deep link ?thread-csv=1, agentctl
journeys, smokes, and docs. Fix pushForumTagExportToMesh naming from pin clone.

Bundle: npm run test:ci-phase704 (50/50). Roadmap Phase 704 complete; Phase 705 slot opened.

headless.js

@@ -3946,6 +3946,47 @@ class HeadlessSession {
     }
   }
 
+  async runThreadArchiveCsvJourney () {
+    if (!this.platform) throw new Error('headless not started')
+    await this.registerUser({ username: 'th704', displayName: 'Thread CSV 704' })
+    await this.createGuild({ name: 'Thread CSV 704', publicListing: false })
+    await this.wait({ mode: 'guild' }, 45000)
+    const row = await this.sendGuildMessage('Phase704 thread archive export seed')
+    await this.ipc({ type: 'create-thread', messageId: row.id, name: 'Archive export thread' })
+    await this.refreshView()
+    const threadId = this._lastView?.activeChannelId
+    if (threadId) await this.platform.archiveThread(threadId, true).catch(() => {})
+    const pushed = await this.platform.pushThreadArchiveCsvToMesh()
+    const v = await this.refreshView()
+    if (!pushed?.signature && !v.threadArchiveCsvMeta?.signature) {
+      throw new Error('expected signed thread archive CSV after mesh push')
+    }
+    return {
+      guildThreadCsvCount: (v.threadArchiveCsvRows || []).length + (v.guildThreads || []).length,
+      hasMeta: v.threadArchiveCsvMeta != null,
+      threadCount: (v.guildThreads || []).length
+    }
+  }
+
+  async runForumTagExportJourney () {
+    if (!this.platform) throw new Error('headless not started')
+    await this.registerUser({ username: 'ft704', displayName: 'Forum Tag 704' })
+    await this.createGuild({ name: 'Forum Tag 704', publicListing: false })
+    await this.wait({ mode: 'guild' }, 45000)
+    await this.createGuildChannel('Forum Tags', { type: 'forum' })
+    await this.refreshView()
+    const pushed = await this.platform.pushForumTagExportToMesh()
+    const v = await this.refreshView()
+    if (!pushed?.signature) {
+      throw new Error('expected signed forum tag CSV export')
+    }
+    return {
+      guildThreadCsvCount: (v.forumTagExportCsvRows || []).length,
+      hasForumExport:
+        v.lastForumTagExport != null || (v.forumTagExportCsvRows || []).length > 0
+    }
+  }
+
   async runForumPostSearchJourney () {
     if (!this.platform) throw new Error('headless not started')
     await this.registerUser({ username: 'fm672', displayName: 'Forum 672' })