mom: add working indicator and improve stop command

Working Indicator:
- Add '...' to channel messages while mom is processing
- Automatically removed when work completes or stops
- Applies to working message, not status messages

Improved Stop Command:
- Posts separate 'Stopping...' message that updates to 'Stopped'
- Original working message continues updating with tool results
- Clean separation between status and work output
- Properly handles abort during multi-step operations

Clean Stop Reason Handling:
- Agent run() now returns { stopReason } instead of throwing
- Handle 'aborted', 'error', 'stop', 'length', 'toolUse' cases cleanly
- No more exception-based control flow
- Track stopReason from assistant message.stopReason field

New SlackContext Methods:
- replaceMessage() - replace message text instead of appending
- setWorking() - add/remove working indicator
- Improved context tracking for stop command updates

packages/mom/CHANGELOG.md

@@ -20,6 +20,13 @@
   - Tracks tokens (input, output, cache read, cache write) and costs per run
   - Displays summary at end of each agent run in console and Slack thread
   - Example: `💰 Usage: 12,543 in + 847 out (5,234 cache read, 127 cache write) = $0.0234`
+- Working indicator in Slack messages
+  - Channel messages show "..." while mom is processing
+  - Automatically removed when work completes
+- Improved stop command behavior
+  - Separate "Stopping..." message that updates to "Stopped" when abort completes
+  - Original working message continues to show tool results (including abort errors)
+  - Clean separation between status and results
 
 ### Changed
 
@@ -42,6 +49,9 @@
 - Tool result display now extracts actual text instead of showing JSON wrapper
 - Slack thread messages now show cleaner tool call formatting with duration and label
 - All console logging centralized and removed from scattered locations
+- Agent run now returns `{ stopReason }` instead of throwing exceptions
+  - Clean handling of "aborted", "error", "stop", "length", "toolUse" cases
+  - No more error-based control flow
 
 ### Fixed
 

packages/mom/src/agent.ts

@@ -13,7 +13,7 @@ import { createMomTools, setUploadFunction } from "./tools/index.js";
 const model = getModel("anthropic", "claude-sonnet-4-5");
 
 export interface AgentRunner {
-	run(ctx: SlackContext, channelDir: string, store: ChannelStore): Promise<void>;
+	run(ctx: SlackContext, channelDir: string, store: ChannelStore): Promise<{ stopReason: string }>;
 	abort(): void;
 }
 
@@ -316,7 +316,7 @@ export function createAgentRunner(sandboxConfig: SandboxConfig): AgentRunner {
 	const executor = createExecutor(sandboxConfig);
 
 	return {
-		async run(ctx: SlackContext, channelDir: string, store: ChannelStore): Promise<void> {
+		async run(ctx: SlackContext, channelDir: string, store: ChannelStore): Promise<{ stopReason: string }> {
 			// Ensure channel directory exists
 			await mkdir(channelDir, { recursive: true });
 
@@ -374,6 +374,9 @@ export function createAgentRunner(sandboxConfig: SandboxConfig): AgentRunner {
 				},
 			};
 
+			// Track stop reason
+			let stopReason = "stop";
+
 			// Subscribe to events
 			agent.subscribe(async (event: AgentEvent) => {
 				switch (event.type) {
@@ -474,6 +477,11 @@ export function createAgentRunner(sandboxConfig: SandboxConfig): AgentRunner {
 						if (event.message.role === "assistant") {
 							const assistantMsg = event.message as any; // AssistantMessage type
 
+							// Track stop reason
+							if (assistantMsg.stopReason) {
+								stopReason = assistantMsg.stopReason;
+							}
+
 							// Accumulate usage
 							if (assistantMsg.usage) {
 								totalUsage.input += assistantMsg.usage.input;
@@ -520,6 +528,8 @@ export function createAgentRunner(sandboxConfig: SandboxConfig): AgentRunner {
 				const summary = log.logUsageSummary(logCtx, totalUsage);
 				await ctx.respondInThread(summary);
 			}
+
+			return { stopReason };
 		},
 
 		abort(): void {

packages/mom/src/main.ts

@@ -68,7 +68,7 @@ if (!MOM_SLACK_APP_TOKEN || !MOM_SLACK_BOT_TOKEN || (!ANTHROPIC_API_KEY && !ANTH
 await validateSandbox(sandbox);
 
 // Track active agent runs per channel
-const activeRuns = new Map<string, AgentRunner>();
+const activeRuns = new Map<string, { runner: AgentRunner; context: SlackContext; stopContext?: SlackContext }>();
 
 async function handleMessage(ctx: SlackContext, _source: "channel" | "dm"): Promise<void> {
 	const channelId = ctx.message.channel;
@@ -82,11 +82,15 @@ async function handleMessage(ctx: SlackContext, _source: "channel" | "dm"): Prom
 
 	// Check for stop command
 	if (messageText === "stop") {
-		const runner = activeRuns.get(channelId);
+		const active = activeRuns.get(channelId);
-		if (runner) {
+		if (active) {
 			log.logStopRequest(logCtx);
-			runner.abort();
+			// Post a NEW message saying "Stopping..."
 			await ctx.respond("_Stopping..._");
+			// Store this context to update it to "Stopped" later
+			active.stopContext = ctx;
+			// Abort the runner
+			active.runner.abort();
 		} else {
 			await ctx.respond("_Nothing running._");
 		}
@@ -103,23 +107,31 @@ async function handleMessage(ctx: SlackContext, _source: "channel" | "dm"): Prom
 	const channelDir = join(workingDir, channelId);
 
 	const runner = createAgentRunner(sandbox);
-	activeRuns.set(channelId, runner);
+	activeRuns.set(channelId, { runner, context: ctx });
 
 	await ctx.setTyping(true);
-	try {
+	await ctx.setWorking(true);
-		await runner.run(ctx, channelDir, ctx.store);
+
-	} catch (error) {
+	const result = await runner.run(ctx, channelDir, ctx.store);
-		// Don't report abort errors
+
-		const msg = error instanceof Error ? error.message : String(error);
+	// Remove working indicator
-		if (msg.includes("aborted") || msg.includes("Aborted")) {
+	await ctx.setWorking(false);
-			// Already said "Stopping..." - nothing more to say
+
-		} else {
+	// Handle different stop reasons
-			log.logAgentError(logCtx, msg);
+	const active = activeRuns.get(channelId);
-			await ctx.respond(`❌ Error: ${msg}`);
+	if (result.stopReason === "aborted") {
+		// Replace the STOP message with "Stopped"
+		if (active?.stopContext) {
+			await active.stopContext.setWorking(false);
+			await active.stopContext.replaceMessage("_Stopped_");
 		}
-	} finally {
+	} else if (result.stopReason === "error") {
+		// Agent encountered an error
+		log.logAgentError(logCtx, "Agent stopped with error");
+	}
+	// "stop", "length", "toolUse" are normal completions - nothing extra to do
+
 	activeRuns.delete(channelId);
-	}
 }
 
 const bot = new MomBot(

packages/mom/src/slack.ts

@@ -21,12 +21,16 @@ export interface SlackContext {
 	store: ChannelStore;
 	/** Send/update the main message (accumulates text) */
 	respond(text: string): Promise<void>;
+	/** Replace the entire message text (not append) */
+	replaceMessage(text: string): Promise<void>;
 	/** Post a message in the thread under the main message (for verbose details) */
 	respondInThread(text: string): Promise<void>;
 	/** Show/hide typing indicator */
 	setTyping(isTyping: boolean): Promise<void>;
 	/** Upload a file to the channel */
 	uploadFile(filePath: string, title?: string): Promise<void>;
+	/** Set working state (adds/removes working indicator emoji) */
+	setWorking(working: boolean): Promise<void>;
 }
 
 export interface MomHandler {
@@ -201,6 +205,8 @@ export class MomBot {
 		let messageTs: string | null = null;
 		let accumulatedText = "";
 		let isThinking = true; // Track if we're still in "thinking" state
+		let isWorking = true; // Track if still processing
+		const workingIndicator = " ...";
 		let updatePromise: Promise<void> = Promise.resolve();
 
 		return {
@@ -227,18 +233,21 @@ export class MomBot {
 						accumulatedText += "\n" + responseText;
 					}
 
+					// Add working indicator if still working
+					const displayText = isWorking ? accumulatedText + workingIndicator : accumulatedText;
+
 					if (messageTs) {
 						// Update existing message
 						await this.webClient.chat.update({
 							channel: event.channel,
 							ts: messageTs,
-							text: accumulatedText,
+							text: displayText,
 						});
 					} else {
 						// Post initial message
 						const result = await this.webClient.chat.postMessage({
 							channel: event.channel,
-							text: accumulatedText,
+							text: displayText,
 						});
 						messageTs = result.ts as string;
 					}
@@ -267,8 +276,8 @@ export class MomBot {
 			},
 			setTyping: async (isTyping: boolean) => {
 				if (isTyping && !messageTs) {
-					// Post initial "thinking" message
+					// Post initial "thinking" message (... auto-appended by working indicator)
-					accumulatedText = "_Thinking..._";
+					accumulatedText = "_Thinking_";
 					const result = await this.webClient.chat.postMessage({
 						channel: event.channel,
 						text: accumulatedText,
@@ -288,6 +297,46 @@ export class MomBot {
 					title: fileName,
 				});
 			},
+			replaceMessage: async (text: string) => {
+				updatePromise = updatePromise.then(async () => {
+					// Replace the accumulated text entirely
+					accumulatedText = text;
+
+					const displayText = isWorking ? accumulatedText + workingIndicator : accumulatedText;
+
+					if (messageTs) {
+						await this.webClient.chat.update({
+							channel: event.channel,
+							ts: messageTs,
+							text: displayText,
+						});
+					} else {
+						// Post initial message
+						const result = await this.webClient.chat.postMessage({
+							channel: event.channel,
+							text: displayText,
+						});
+						messageTs = result.ts as string;
+					}
+				});
+				await updatePromise;
+			},
+			setWorking: async (working: boolean) => {
+				updatePromise = updatePromise.then(async () => {
+					isWorking = working;
+
+					// If we have a message, update it to add/remove indicator
+					if (messageTs) {
+						const displayText = isWorking ? accumulatedText + workingIndicator : accumulatedText;
+						await this.webClient.chat.update({
+							channel: event.channel,
+							ts: messageTs,
+							text: displayText,
+						});
+					}
+				});
+				await updatePromise;
+			},
 		};
 	}