fix: arbiter session collision — separate session folder + always fresh session

- resolveSessionFolder now always returns unique folder for arbiter
  (prevents sharing session with owner when both use same agent type)
- Arbiter sessionId forced to undefined to prevent resume attempts

src/db.ts

@@ -1137,6 +1137,18 @@ export function getLastHumanMessageTimestamp(chatJid: string): string | null {
   return row?.timestamp ?? null;
 }
 
+export function getLastHumanMessageSender(chatJid: string): string | null {
+  const row = db
+    .prepare(
+      `SELECT sender FROM messages
+       WHERE chat_jid = ? AND is_bot_message = 0 AND is_from_me = 0
+         AND content != '' AND content IS NOT NULL
+       ORDER BY timestamp DESC, seq DESC LIMIT 1`,
+    )
+    .get(chatJid) as { sender: string } | undefined;
+  return row?.sender ?? null;
+}
+
 export function getLastHumanMessageContent(chatJid: string): string | null {
   const row = db
     .prepare(

src/message-agent-executor.ts

@@ -14,8 +14,10 @@ import { listAvailableGroups } from './available-groups.js';
 import {
   createServiceHandoff,
   getAllTasks,
+  getLastHumanMessageSender,
   getLatestOpenPairedTaskForChat,
   getLatestTurnNumber,
+  getPairedTaskById,
   insertPairedTurnOutput,
 } from './db.js';
 import { GroupQueue } from './group-queue.js';
@@ -128,7 +130,8 @@ export async function runAgentForGroup(
     activeRole,
     group.agentType,
   );
-  const sessionId = sessions[sessionFolder];
+  // Arbiter always starts fresh — never resume a previous session
+  const sessionId = activeRole === 'arbiter' ? undefined : sessions[sessionFolder];
   const memoryBriefing = sessionId
     ? undefined
     : await buildRoomMemoryBriefing({

src/message-runtime-rules.ts

@@ -89,6 +89,8 @@ export function resolveSessionFolder(
   role: 'owner' | 'reviewer' | 'arbiter',
   groupAgentType: AgentType | undefined,
 ): string {
+  // Arbiter always gets a separate session — must never share with owner/reviewer
+  if (role === 'arbiter') return `${groupFolder}:arbiter`;
   const effectiveType = resolveEffectiveAgentType(role, groupAgentType);
   const groupDefault: AgentType = groupAgentType || 'claude-code';
   if (effectiveType === groupDefault) return groupFolder;