diff --git a/extensions/slack/src/actions.ts b/extensions/slack/src/actions.ts
index f1dbd45b9af..58ca16e9b9f 100644
--- a/extensions/slack/src/actions.ts
+++ b/extensions/slack/src/actions.ts
@@ -3,15 +3,13 @@ import type { OpenClawConfig } from "openclaw/plugin-sdk/config-types";
 import { requireRuntimeConfig } from "openclaw/plugin-sdk/plugin-config-runtime";
 import { logVerbose } from "openclaw/plugin-sdk/runtime-env";
 import { resolveSlackAccount } from "./accounts.js";
-import { buildSlackBlocksFallbackText } from "./blocks-fallback.js";
 import { validateSlackBlocksArray } from "./blocks-input.js";
 import { createSlackWebClient, getSlackWriteClient } from "./client.js";
-import { SLACK_TEXT_LIMIT } from "./limits.js";
+import { buildSlackEditTextPayload } from "./edit-text.js";
 import { resolveSlackMedia } from "./monitor/media.js";
 import type { SlackMediaResult } from "./monitor/media.js";
 import { sendMessageSlack } from "./send.js";
 import { resolveSlackBotToken } from "./token.js";
-import { truncateSlackText } from "./truncate.js";
 
 export type SlackActionClientOpts = {
   cfg?: OpenClawConfig;
@@ -232,13 +230,10 @@ export async function editSlackMessage(
 ) {
   const client = await getClient(opts, "write");
   const blocks = opts.blocks == null ? undefined : validateSlackBlocksArray(opts.blocks);
-  const trimmedContent = content.trim();
   await client.chat.update({
     channel: channelId,
     ts: messageId,
-    text:
-      trimmedContent ||
-      (blocks ? truncateSlackText(buildSlackBlocksFallbackText(blocks), SLACK_TEXT_LIMIT) : " "),
+    text: buildSlackEditTextPayload(content, blocks),
     ...(blocks ? { blocks } : {}),
   });
 }
diff --git a/extensions/slack/src/edit-text.ts b/extensions/slack/src/edit-text.ts
new file mode 100644
index 00000000000..f265047413c
--- /dev/null
+++ b/extensions/slack/src/edit-text.ts
@@ -0,0 +1,18 @@
+import type { Block, KnownBlock } from "@slack/web-api";
+import { buildSlackBlocksFallbackText } from "./blocks-fallback.js";
+import { SLACK_TEXT_LIMIT } from "./limits.js";
+import { truncateSlackText } from "./truncate.js";
+
+export function buildSlackEditTextPayload(
+  content: string,
+  blocks?: (Block | KnownBlock)[],
+): string {
+  const trimmedContent = content.trim();
+  if (trimmedContent) {
+    return trimmedContent;
+  }
+  if (blocks?.length) {
+    return truncateSlackText(buildSlackBlocksFallbackText(blocks), SLACK_TEXT_LIMIT);
+  }
+  return " ";
+}
diff --git a/extensions/slack/src/monitor/message-handler/preview-finalize.test.ts b/extensions/slack/src/monitor/message-handler/preview-finalize.test.ts
index 3a55406ada6..6bdb9365b22 100644
--- a/extensions/slack/src/monitor/message-handler/preview-finalize.test.ts
+++ b/extensions/slack/src/monitor/message-handler/preview-finalize.test.ts
@@ -108,4 +108,41 @@ describe("finalizeSlackPreviewEdit", () => {
       }),
     ).toBe("*Done*");
   });
+
+  it("matches truncated fallback text for long blocks-only edit readback", async () => {
+    const longContextText = "a".repeat(3000);
+    const blocks = [
+      {
+        type: "context",
+        elements: [
+          { type: "mrkdwn", text: longContextText },
+          { type: "mrkdwn", text: longContextText },
+          { type: "mrkdwn", text: longContextText },
+        ],
+      },
+    ] as const;
+    const expectedText = __testing.buildExpectedSlackEditText({
+      text: "",
+      blocks: blocks as unknown as Parameters<
+        typeof __testing.buildExpectedSlackEditText
+      >[0]["blocks"],
+    });
+    const client = createClient({
+      historyMessages: [{ ts: "171234.567", text: expectedText, blocks }],
+    });
+
+    expect(expectedText).toHaveLength(8000);
+    await expect(
+      __testing.didSlackPreviewEditApplyAfterError({
+        client,
+        token: "xoxb-test",
+        channelId: "C123",
+        messageId: "171234.567",
+        text: "",
+        blocks: blocks as unknown as Parameters<
+          typeof __testing.didSlackPreviewEditApplyAfterError
+        >[0]["blocks"],
+      }),
+    ).resolves.toBe(true);
+  });
 });
diff --git a/extensions/slack/src/monitor/message-handler/preview-finalize.ts b/extensions/slack/src/monitor/message-handler/preview-finalize.ts
index b970e67daf3..12576663446 100644
--- a/extensions/slack/src/monitor/message-handler/preview-finalize.ts
+++ b/extensions/slack/src/monitor/message-handler/preview-finalize.ts
@@ -1,7 +1,7 @@
 import type { Block, KnownBlock, WebClient } from "@slack/web-api";
 import { logVerbose } from "openclaw/plugin-sdk/runtime-env";
 import { editSlackMessage } from "../../actions.js";
-import { buildSlackBlocksFallbackText } from "../../blocks-fallback.js";
+import { buildSlackEditTextPayload } from "../../edit-text.js";
 import { normalizeSlackOutboundText } from "../../format.js";
 
 type SlackReadbackMessage = {
@@ -14,14 +14,7 @@ function buildExpectedSlackEditText(params: {
   text: string;
   blocks?: (Block | KnownBlock)[];
 }): string {
-  const trimmed = normalizeSlackOutboundText(params.text.trim());
-  if (trimmed) {
-    return trimmed;
-  }
-  if (params.blocks?.length) {
-    return buildSlackBlocksFallbackText(params.blocks);
-  }
-  return " ";
+  return buildSlackEditTextPayload(params.text, params.blocks);
 }
 
 function blocksMatch(expected?: (Block | KnownBlock)[], actual?: unknown[]): boolean {