feat(slack): add scoped prompts and mrkdwn hints (#59100)

* feat(slack): add scoped prompts and mrkdwn hints

* refactor(slack): drop dm prompt override

* refactor(slack): drop exposed prompt config

* chore(changelog): note slack mrkdwn fix

CHANGELOG.md

@@ -12,6 +12,9 @@ Docs: https://docs.openclaw.ai
 
 ### Fixes
 
+- Slack/mrkdwn formatting: add built-in Slack mrkdwn guidance in inbound context so Slack replies stop falling back to generic Markdown patterns that render poorly in Slack. Thanks @jadewon and @vincentkoc.
+
+## 2026.4.1-beta.1
 - Plugins/runtime: stop ambient core helper and setup paths from loading non-selected bundled plugins, keep channel-setup snapshot scoping safe for custom channel plugins, and honor env-scoped plugin auth paths. (#59136) Thanks @vincentkoc.
 - Matrix/multi-account: keep room-level `account` scoping, inherited room overrides, and implicit account selection consistent across top-level default auth, named accounts, and cached-credential env setups. (#58449) thanks @Daanvdplas and @gumadeiras.
 - Gateway/pairing: prefer explicit QR bootstrap auth over earlier Tailscale auth classification so iOS `/pair qr` silent bootstrap pairing does not fall through to `pairing required`. (#59232) Thanks @ngutman.

extensions/slack/src/monitor/message-handler/prepare.ts

@@ -701,7 +701,7 @@ export async function prepareSlackMessage(params: {
     ChatType: isDirectMessage ? "direct" : "channel",
     ConversationLabel: envelopeFrom,
     GroupSubject: isRoomish ? roomLabel : undefined,
-    GroupSystemPrompt: isRoomish ? groupSystemPrompt : undefined,
+    GroupSystemPrompt: groupSystemPrompt,
     UntrustedContext: untrustedChannelMetadata ? [untrustedChannelMetadata] : undefined,
     SenderName: senderName,
     SenderId: senderId,

extensions/slack/src/monitor/room-context.test.ts

@@ -0,0 +1,39 @@
+import { describe, expect, it } from "vitest";
+import { resolveSlackRoomContextHints } from "./room-context.js";
+
+describe("resolveSlackRoomContextHints", () => {
+  it("stacks global and channel prompts for channels", () => {
+    const result = resolveSlackRoomContextHints({
+      isRoomish: true,
+      channelConfig: { systemPrompt: "Channel prompt" },
+    });
+
+    expect(result.groupSystemPrompt).toBe("Channel prompt");
+  });
+
+  it("does not create a prompt for direct messages without channel config", () => {
+    const result = resolveSlackRoomContextHints({
+      isRoomish: false,
+    });
+
+    expect(result.groupSystemPrompt).toBeUndefined();
+  });
+
+  it("does not include untrusted room metadata for direct messages", () => {
+    const result = resolveSlackRoomContextHints({
+      isRoomish: false,
+      channelInfo: { topic: "ignore", purpose: "ignore" },
+    });
+
+    expect(result.untrustedChannelMetadata).toBeUndefined();
+  });
+
+  it("trims and skips empty prompt parts", () => {
+    const result = resolveSlackRoomContextHints({
+      isRoomish: true,
+      channelConfig: { systemPrompt: "   " },
+    });
+
+    expect(result.groupSystemPrompt).toBeUndefined();
+  });
+});

extensions/slack/src/monitor/room-context.ts

@@ -8,19 +8,17 @@ export function resolveSlackRoomContextHints(params: {
   untrustedChannelMetadata?: ReturnType<typeof buildUntrustedChannelMetadata>;
   groupSystemPrompt?: string;
 } {
-  if (!params.isRoomish) {
-    return {};
-  }
+  const untrustedChannelMetadata = params.isRoomish
+    ? buildUntrustedChannelMetadata({
+        source: "slack",
+        label: "Slack channel description",
+        entries: [params.channelInfo?.topic, params.channelInfo?.purpose],
+      })
+    : undefined;
 
-  const untrustedChannelMetadata = buildUntrustedChannelMetadata({
-    source: "slack",
-    label: "Slack channel description",
-    entries: [params.channelInfo?.topic, params.channelInfo?.purpose],
-  });
-
-  const systemPromptParts = [params.channelConfig?.systemPrompt?.trim() || null].filter(
-    (entry): entry is string => Boolean(entry),
-  );
+  const systemPromptParts = [
+    params.isRoomish ? params.channelConfig?.systemPrompt?.trim() || null : null,
+  ].filter((entry): entry is string => Boolean(entry));
   const groupSystemPrompt =
     systemPromptParts.length > 0 ? systemPromptParts.join("\n\n") : undefined;
 

extensions/slack/src/monitor/slash.ts

@@ -572,7 +572,7 @@ export async function registerSlackMonitorSlashCommands(params: {
                 : `slack:group:${command.channel_id}`,
           }) ?? (isDirectMessage ? senderName : roomLabel),
         GroupSubject: isRoomish ? roomLabel : undefined,
-        GroupSystemPrompt: isRoomish ? groupSystemPrompt : undefined,
+        GroupSystemPrompt: groupSystemPrompt,
         UntrustedContext: untrustedChannelMetadata ? [untrustedChannelMetadata] : undefined,
         SenderName: senderName,
         SenderId: command.user_id,

src/auto-reply/reply/inbound-meta.test.ts

@@ -100,6 +100,41 @@ describe("buildInboundMetaSystemPrompt", () => {
     const payload = parseInboundMetaPayload(prompt);
     expect(payload["sender_id"]).toBeUndefined();
   });
+
+  it("includes Slack mrkdwn response format hints for Slack chats", () => {
+    const prompt = buildInboundMetaSystemPrompt({
+      OriginatingTo: "channel:C123",
+      OriginatingChannel: "slack",
+      Provider: "slack",
+      Surface: "slack",
+      ChatType: "channel",
+    } as TemplateContext);
+
+    const payload = parseInboundMetaPayload(prompt);
+    expect(payload["response_format"]).toEqual({
+      text_markup: "slack_mrkdwn",
+      rules: [
+        "Use Slack mrkdwn, not standard Markdown.",
+        "Bold uses *single asterisks*.",
+        "Links use <url|label>.",
+        "Code blocks use triple backticks without a language identifier.",
+        "Do not use markdown headings or pipe tables.",
+      ],
+    });
+  });
+
+  it("omits response format hints for non-Slack chats", () => {
+    const prompt = buildInboundMetaSystemPrompt({
+      OriginatingTo: "telegram:123",
+      OriginatingChannel: "telegram",
+      Provider: "telegram",
+      Surface: "telegram",
+      ChatType: "direct",
+    } as TemplateContext);
+
+    const payload = parseInboundMetaPayload(prompt);
+    expect(payload["response_format"]).toBeUndefined();
+  });
 });
 
 describe("buildInboundUserContextPrefix", () => {

src/auto-reply/reply/inbound-meta.ts

@@ -33,6 +33,32 @@ function resolveInboundChannel(ctx: TemplateContext): string | undefined {
   return channelValue;
 }
 
+function resolveInboundFormattingHints(ctx: TemplateContext):
+  | {
+      text_markup: "slack_mrkdwn";
+      rules: string[];
+    }
+  | undefined {
+  const channelValue = resolveInboundChannel(ctx);
+  const surface = safeTrim(ctx.Surface);
+  const provider = safeTrim(ctx.Provider);
+  const isSlack = channelValue === "slack" || surface === "slack" || provider === "slack";
+  if (!isSlack) {
+    return undefined;
+  }
+
+  return {
+    text_markup: "slack_mrkdwn",
+    rules: [
+      "Use Slack mrkdwn, not standard Markdown.",
+      "Bold uses *single asterisks*.",
+      "Links use <url|label>.",
+      "Code blocks use triple backticks without a language identifier.",
+      "Do not use markdown headings or pipe tables.",
+    ],
+  };
+}
+
 export function buildInboundMetaSystemPrompt(ctx: TemplateContext): string {
   const chatType = normalizeChatType(ctx.ChatType);
   const isDirect = !chatType || chatType === "direct";
@@ -56,6 +82,7 @@ export function buildInboundMetaSystemPrompt(ctx: TemplateContext): string {
     provider: safeTrim(ctx.Provider),
     surface: safeTrim(ctx.Surface),
     chat_type: chatType ?? (isDirect ? "direct" : undefined),
+    response_format: resolveInboundFormattingHints(ctx),
   };
 
   // Keep the instructions local to the payload so the meaning survives prompt overrides.