fix: cap slack block fallback text

CHANGELOG.md

@@ -77,6 +77,7 @@ Docs: https://docs.openclaw.ai
 - Slack/commands: cap native command argument-menu fallback rows to Slack's message block limit, so large plugin choice lists no longer make Slack reject the generated menu. Thanks @slackapi.
 - Slack/commands: drop fallback command argument buttons whose encoded values exceed Slack's button-value limit, so one oversized plugin choice no longer makes Slack reject the whole menu. Thanks @slackapi.
 - Slack/messages: merge message-tool presentation and interactive blocks on Slack sends, so buttons and selects are no longer dropped when a structured message body is also present. Thanks @slackapi.
+- Slack/messages: cap Block Kit fallback text to Slack's send limit while preserving the rendered blocks, so long context fallbacks no longer make rich Slack messages fail with `msg_too_long`. Thanks @slackapi.
 - Channels/WhatsApp: require Baileys outbound message ids before marking auto-replies delivered, so transcript text and ack reactions no longer make failed group replies look sent. Fixes #49225. Thanks @TinyTb.
 - CLI/update: scope packaged Node compile caches by OpenClaw version and install metadata, so global installs no longer reuse stale compiled chunks after package updates. Thanks @pashpashpash.
 - Channels/Voice call: keep pre-auth webhook in-flight limiting active when socket remote address metadata is missing, so slow-body requests from stripped-IP proxy paths still share the fallback bucket. (#74453) Thanks @davidangularme.

extensions/slack/src/send.blocks.test.ts

@@ -4,6 +4,7 @@ import { createSlackSendTestClient, installSlackBlockTestMocks } from "./blocks.
 installSlackBlockTestMocks();
 const { sendMessageSlack } = await import("./send.js");
 const SLACK_TEST_CFG = { channels: { slack: { botToken: "xoxb-test" } } };
+const SLACK_TEXT_LIMIT = 8000;
 
 describe("sendMessageSlack NO_REPLY guard", () => {
   it("suppresses NO_REPLY text before any Slack API call", async () => {
@@ -170,6 +171,36 @@ describe("sendMessageSlack blocks", () => {
     );
   });
 
+  it("caps long fallback text while preserving blocks", async () => {
+    const client = createSlackSendTestClient();
+    const longContextText = "a".repeat(3000);
+    const blocks = [
+      {
+        type: "context",
+        elements: [
+          { type: "mrkdwn", text: longContextText },
+          { type: "mrkdwn", text: longContextText },
+          { type: "mrkdwn", text: longContextText },
+        ],
+      },
+    ];
+
+    await sendMessageSlack("channel:C123", "", {
+      token: "xoxb-test",
+      cfg: SLACK_TEST_CFG,
+      client,
+      blocks,
+    });
+
+    expect(client.chat.postMessage).toHaveBeenCalledWith(
+      expect.objectContaining({
+        text: expect.stringMatching(/…$/),
+        blocks,
+      }),
+    );
+    expect(client.chat.postMessage.mock.calls[0]?.[0].text).toHaveLength(SLACK_TEXT_LIMIT);
+  });
+
   it("rejects blocks combined with mediaUrl", async () => {
     const client = createSlackSendTestClient();
     await expect(

extensions/slack/src/send.ts

@@ -26,6 +26,7 @@ import { SLACK_TEXT_LIMIT } from "./limits.js";
 import { loadOutboundMediaFromUrl } from "./runtime-api.js";
 import { parseSlackTarget } from "./targets.js";
 import { resolveSlackBotToken } from "./token.js";
+import { truncateSlackText } from "./truncate.js";
 const SLACK_UPLOAD_SSRF_POLICY = {
   allowedHostnames: ["*.slack.com", "*.slack-edge.com", "*.slack-files.com"],
   allowRfc2544BenchmarkRange: true,
@@ -411,7 +412,10 @@ async function sendMessageSlackQueued(params: {
     if (opts.mediaUrl) {
       throw new Error("Slack send does not support blocks with mediaUrl");
     }
-    const fallbackText = trimmedMessage || buildSlackBlocksFallbackText(blocks);
+    const fallbackText = truncateSlackText(
+      trimmedMessage || buildSlackBlocksFallbackText(blocks),
+      SLACK_TEXT_LIMIT,
+    );
     const response = await postSlackMessageBestEffort({
       client,
       channelId,