mom: fix duplicate logging

- Remove user message logging from agent.ts (Slack handler already logs it)
- Add excludeTimestamp param to syncFromLog to skip current @mention
- Sync happens once before each prompt with current message excluded

packages/mom/src/agent.ts

@@ -337,11 +337,12 @@ export function createAgentRunner(sandboxConfig: SandboxConfig): AgentRunner {
 
 				// Update system prompt for existing session (memory may have changed)
 				session.agent.setSystemPrompt(systemPrompt);
-
-				// Sync any new messages from log.jsonl (e.g., messages that arrived while processing)
-				sessionManager.syncFromLog();
 			}
 
+			// Sync messages from log.jsonl to context.jsonl
+			// Exclude the current message - it will be added via prompt()
+			sessionManager.syncFromLog(ctx.message.ts);
+
 			currentSession = session;
 
 			// Create logging context
@@ -551,19 +552,9 @@ export function createAgentRunner(sandboxConfig: SandboxConfig): AgentRunner {
 
 			try {
 				// Build user message from Slack context
+				// Note: User message is already logged to log.jsonl by Slack event handler
 				const userMessage = ctx.message.text;
 
-				// Log user message to log.jsonl (human-readable history)
-				await store.logMessage(ctx.message.channel, {
-					date: new Date().toISOString(),
-					ts: toSlackTs(),
-					user: ctx.message.user,
-					userName: ctx.message.userName,
-					text: userMessage,
-					attachments: ctx.message.attachments || [],
-					isBot: false,
-				});
-
 				// Send prompt to agent session
 				await session.prompt(userMessage);
 

packages/mom/src/context.ts

@@ -70,9 +70,7 @@ export class MomSessionManager {
 		} else {
 			this.sessionId = uuidv4();
 		}
-
-		// Sync missing messages from log.jsonl to context.jsonl
-		this.syncFromLog();
+		// Note: syncFromLog() is called explicitly from agent.ts with excludeTimestamp
 	}
 
 	/**
@@ -87,8 +85,10 @@ export class MomSessionManager {
 	 * Channel chatter is formatted as "[username]: message" to distinguish from direct @mentions.
 	 *
 	 * Called automatically on construction and should be called before each agent run.
+	 *
+	 * @param excludeTimestamp Optional timestamp to exclude (for the current @mention being processed)
 	 */
-	syncFromLog(): void {
+	syncFromLog(excludeTimestamp?: string): void {
 		if (!existsSync(this.logFile)) return;
 
 		// Get timestamps of messages already in context
@@ -118,12 +118,17 @@ export class MomSessionManager {
 			try {
 				const logMsg: LogMessage = JSON.parse(line);
 
+				// Use date for context timestamp (consistent key)
 				const ts = logMsg.date || logMsg.ts;
 				if (!ts) continue;
 
 				// Skip if already in context
 				if (contextTimestamps.has(ts)) continue;
 
+				// Skip the current message being processed (will be added via prompt())
+				// Compare against Slack ts since that's what ctx.message.ts provides
+				if (excludeTimestamp && logMsg.ts === excludeTimestamp) continue;
+
 				// Skip bot messages - added through agent flow
 				if (logMsg.isBot) continue;