fix(slack): truncate rich text preview on UTF-16 boundary

Leon-SK668 · Leon-SK668 · commit 21450b1fc293 · 2026-06-26T11:48:49.000+08:00
summarizeRichTextPreview truncated the block-action rich text preview
with String.slice(0, 119) on a UTF-16 code-unit index, so an astral
character straddling the 120-char boundary was cut into a lone
surrogate in the interaction summary preview.

Use truncateUtf16Safe so truncation never splits a surrogate pair,
keeping the existing 120-char budget and ellipsis suffix.

Adds tests driving the block_actions handler with a rich_text_input at
the truncation boundary, asserting the preview stays UTF-16 well formed
and that a complete emoji is kept when it fits.
diff --git a/extensions/slack/src/monitor/events/interactions.block-actions.ts b/extensions/slack/src/monitor/events/interactions.block-actions.ts
@@ -21,6 +21,7 @@ import {
   SLACK_REPLY_BUTTON_ACTION_ID,
   SLACK_REPLY_SELECT_ACTION_ID,
 } from "../../reply-action-ids.js";
+import { truncateSlackText } from "../../truncate.js";
 import {
   authorizeSlackSystemEventSender,
   resolveSlackCommandIngress,
@@ -173,7 +174,7 @@ function summarizeRichTextPreview(value: unknown): string | undefined {
     return undefined;
   }
   const max = 120;
-  return joined.length <= max ? joined : `${joined.slice(0, max - 1)}…`;
+  return joined.length <= max ? joined : truncateSlackText(joined, max);
 }
 
 function readInteractionAction(raw: unknown) {
diff --git a/extensions/slack/src/monitor/events/interactions.test.ts b/extensions/slack/src/monitor/events/interactions.test.ts
@@ -346,6 +346,13 @@ function requireRecord(value: unknown, label: string): Record<string, unknown> {
   return value as Record<string, unknown>;
 }
 
+function hasLoneSurrogate(value: string): boolean {
+  return Array.from(value).some((char) => {
+    const codePoint = char.codePointAt(0) ?? 0;
+    return codePoint >= 0xd800 && codePoint <= 0xdfff;
+  });
+}
+
 function expectRecordFields(
   actual: Record<string, unknown>,
   expected: Record<string, unknown>,
@@ -3190,5 +3197,88 @@ describe("registerSlackInteractionEvents", () => {
     expect(Array.isArray(payload.inputs) ? payload.inputs.length : 0).toBeLessThanOrEqual(3);
     expect((payload.inputsOmitted ?? 0) >= 1).toBe(true);
   });
+
+  it("keeps block action rich text previews UTF-16 safe at the truncation boundary", async () => {
+    enqueueSystemEventMock.mockClear();
+    const { ctx, getHandler } = createContext();
+    registerSlackInteractionEvents({ ctx: ctx as never });
+    const handler = getHandler();
+
+    const boundaryText = `${"x".repeat(118)}😀y`;
+    const ack = vi.fn().mockResolvedValue(undefined);
+    await handler({
+      ack,
+      body: {
+        user: { id: "U555" },
+        channel: { id: "C1" },
+        message: {
+          ts: "111.222",
+          text: "fallback",
+          blocks: [{ type: "actions", block_id: "richtext_block", elements: [] }],
+        },
+      },
+      action: {
+        type: "rich_text_input",
+        action_id: "openclaw:richtext",
+        block_id: "richtext_block",
+        rich_text_value: {
+          type: "rich_text",
+          elements: [
+            {
+              type: "rich_text_section",
+              elements: [{ type: "text", text: boundaryText }],
+            },
+          ],
+        },
+      },
+    } as never);
+
+    expect(ack).toHaveBeenCalled();
+    const payload = slackInteractionPayload() as { richTextPreview?: string };
+    expect(payload.richTextPreview).toBe(`${"x".repeat(118)}…`);
+    expect(payload.richTextPreview?.length).toBeLessThanOrEqual(120);
+    expect(hasLoneSurrogate(payload.richTextPreview ?? "")).toBe(false);
+    expect(() => encodeURIComponent(payload.richTextPreview ?? "")).not.toThrow();
+  });
+
+  it("keeps complete emoji in rich text previews when the UTF-16 boundary can include it", async () => {
+    enqueueSystemEventMock.mockClear();
+    const { ctx, getHandler } = createContext();
+    registerSlackInteractionEvents({ ctx: ctx as never });
+    const handler = getHandler();
+
+    const text = `${"x".repeat(117)}😀yy`;
+    await handler({
+      ack: vi.fn().mockResolvedValue(undefined),
+      body: {
+        user: { id: "U555" },
+        channel: { id: "C1" },
+        message: {
+          ts: "111.333",
+          text: "fallback",
+          blocks: [{ type: "actions", block_id: "richtext_block", elements: [] }],
+        },
+      },
+      action: {
+        type: "rich_text_input",
+        action_id: "openclaw:richtext",
+        block_id: "richtext_block",
+        rich_text_value: {
+          type: "rich_text",
+          elements: [
+            {
+              type: "rich_text_section",
+              elements: [{ type: "text", text }],
+            },
+          ],
+        },
+      },
+    } as never);
+
+    const payload = slackInteractionPayload() as { richTextPreview?: string };
+    expect(payload.richTextPreview).toBe(`${"x".repeat(117)}😀…`);
+    expect(payload.richTextPreview?.length).toBeLessThanOrEqual(120);
+    expect(hasLoneSurrogate(payload.richTextPreview ?? "")).toBe(false);
+  });
 });
 const selectedDateTimeEpoch = 1_771_632_300;
