fix(skills): apply command description limits per channel (#99593)

* fix(skills): keep command spec descriptions UTF-16 safe at the truncation cut

* chore: fix oxlint no-unnecessary-type-assertion in test

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* chore: fix Skill type completeness in test fixture

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* fix(skills): prove UTF-16-safe command truncation

* fix(skills): apply description limits per channel

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>
Co-authored-by: Peter Steinberger <steipete@gmail.com>

extensions/discord/src/monitor/native-command.options.test.ts

@@ -580,8 +580,8 @@ describe("createDiscordNativeCommand option wiring", () => {
     expect(respond).toHaveBeenCalledWith([]);
   });
 
-  it("truncates Discord command and option descriptions to Discord's limit", () => {
-    const longDescription = "x".repeat(140);
+  it("truncates Discord command and option descriptions on a UTF-16 boundary", () => {
+    const longDescription = `${"x".repeat(99)}😀 trailing`;
     const cfg = {} as OpenClawConfig;
     const discordConfig = {} as NonNullable<OpenClawConfig["channels"]>["discord"];
     const command = createDiscordNativeCommand({
@@ -606,14 +606,12 @@ describe("createDiscordNativeCommand option wiring", () => {
       threadBindings: createNoopThreadBindingManager("default"),
     });
 
-    expect(command.description).toHaveLength(100);
-    expect(command.description).toBe("x".repeat(100));
-    expect(requireOption(command, "input").description).toHaveLength(100);
-    expect(requireOption(command, "input").description).toBe("x".repeat(100));
+    expect(command.description).toBe("x".repeat(99));
+    expect(requireOption(command, "input").description).toBe("x".repeat(99));
   });
 
-  it("serializes localized command descriptions", () => {
-    const longDescription = "k".repeat(140);
+  it("serializes localized command descriptions on a UTF-16 boundary", () => {
+    const longDescription = `${"k".repeat(99)}😀 trailing`;
     const command = createDiscordNativeCommand({
       command: {
         name: "localized",
@@ -634,14 +632,14 @@ describe("createDiscordNativeCommand option wiring", () => {
 
     expect(command.descriptionLocalizations).toEqual({
       ko: "현지화된 설명",
-      "en-GB": "k".repeat(100),
+      "en-GB": "k".repeat(99),
     });
     expect(command.serialize()).toEqual({
       name: "localized",
       description: "Default description",
       description_localizations: {
         ko: "현지화된 설명",
-        "en-GB": "k".repeat(100),
+        "en-GB": "k".repeat(99),
       },
       type: ApplicationCommandType.ChatInput,
       integration_types: [0, 1],

extensions/discord/src/monitor/native-command.options.ts

@@ -8,6 +8,7 @@ import {
 } from "openclaw/plugin-sdk/native-command-registry";
 import { createSubsystemLogger } from "openclaw/plugin-sdk/runtime-env";
 import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/string-coerce-runtime";
+import { truncateUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
 import type { AutocompleteInteraction, CommandOptions } from "../internal/discord.js";
 
 const log = createSubsystemLogger("discord/native-command");
@@ -27,7 +28,7 @@ export function truncateDiscordCommandDescription(params: {
   log.warn(
     `discord: truncating native command description (${label}) from ${value.length} to ${DISCORD_COMMAND_DESCRIPTION_MAX}: ${JSON.stringify(value)}`,
   );
-  return value.slice(0, DISCORD_COMMAND_DESCRIPTION_MAX);
+  return truncateUtf16Safe(value, DISCORD_COMMAND_DESCRIPTION_MAX);
 }
 
 export function truncateDiscordCommandDescriptionLocalizations(params: {

extensions/mattermost/src/mattermost/slash-commands.test.ts

@@ -14,6 +14,7 @@ import {
 describe("slash-commands", () => {
   async function registerSingleStatusCommand(
     requestImpl: (path: string, init?: RequestInit) => Promise<unknown>,
+    description = "status",
   ) {
     const client: MattermostClient = {
       baseUrl: "https://chat.example.com",
@@ -30,7 +31,7 @@ describe("slash-commands", () => {
       commands: [
         {
           trigger: "oc_status",
-          description: "status",
+          description,
           autoComplete: true,
         },
       ],
@@ -162,6 +163,37 @@ describe("slash-commands", () => {
     expect(request).toHaveBeenCalledTimes(1);
   });
 
+  it("truncates command descriptions to Mattermost's UTF-8 byte limit", async () => {
+    const description = `${"x".repeat(127)}😀 trailing`;
+    const request = vi.fn(async (path: string, init?: RequestInit) => {
+      if (path.startsWith("/commands?team_id=")) {
+        return [];
+      }
+      if (path === "/commands" && init?.method === "POST") {
+        const body = JSON.parse(typeof init.body === "string" ? init.body : "{}");
+        expect(body.description).toBe("x".repeat(127));
+        expect(body.auto_complete_desc).toBe("x".repeat(127));
+        expect(Buffer.byteLength(body.description, "utf8")).toBeLessThanOrEqual(128);
+        return {
+          id: "cmd-1",
+          token: "tok-1",
+          team_id: "team-1",
+          creator_id: "bot-user",
+          trigger: "oc_status",
+          method: MATTERMOST_SLASH_POST_METHOD,
+          url: "http://gateway/callback",
+          auto_complete: true,
+        };
+      }
+      throw new Error(`unexpected request path: ${path}`);
+    });
+
+    const result = await registerSingleStatusCommand(request, description);
+
+    expect(result).toHaveLength(1);
+    expect(request).toHaveBeenCalledTimes(2);
+  });
+
   it("skips foreign command trigger collisions instead of mutating non-owned commands", async () => {
     const request = vi.fn(async (path: string, init?: { method?: string }) => {
       if (path.startsWith("/commands?team_id=")) {

extensions/mattermost/src/mattermost/slash-commands.ts

@@ -5,6 +5,26 @@ import type { MattermostClient } from "./client.js";
 // ─── Types ───────────────────────────────────────────────────────────────────
 
 export const MATTERMOST_SLASH_POST_METHOD = "P";
+const MATTERMOST_COMMAND_DESCRIPTION_MAX_BYTES = 128;
+
+// Mattermost rejects command descriptions above 128 UTF-8 bytes. Keep portable
+// descriptions intact until this API boundary so other channels retain their text.
+function truncateMattermostCommandDescription(description: string): string {
+  if (Buffer.byteLength(description, "utf8") <= MATTERMOST_COMMAND_DESCRIPTION_MAX_BYTES) {
+    return description;
+  }
+  let bytes = 0;
+  let end = 0;
+  for (const char of description) {
+    const charBytes = Buffer.byteLength(char, "utf8");
+    if (bytes + charBytes > MATTERMOST_COMMAND_DESCRIPTION_MAX_BYTES) {
+      break;
+    }
+    bytes += charBytes;
+    end += char.length;
+  }
+  return description.slice(0, end);
+}
 
 export type MattermostSlashCommandConfig = {
   /** Enable native slash commands. "auto" resolves to false for now (opt-in). */
@@ -177,7 +197,8 @@ export const DEFAULT_COMMAND_SPECS: MattermostCommandSpec[] = [
     originalName: "queue",
     description: "Adjust active-run queue behavior",
     autoComplete: true,
-    autoCompleteHint: "[steer|followup|collect|interrupt] [debounce:2s] [cap:N] [drop:old|new|summarize]",
+    autoCompleteHint:
+      "[steer|followup|collect|interrupt] [debounce:2s] [cap:N] [drop:old|new|summarize]",
   },
 ];
 
@@ -290,6 +311,7 @@ export async function registerSlashCommands(params: {
   const registered: MattermostRegisteredCommand[] = [];
 
   for (const spec of commands) {
+    const description = truncateMattermostCommandDescription(spec.description);
     const existingForTrigger = existingByTrigger.get(spec.trigger) ?? [];
     const ownedCommands = existingForTrigger.filter(
       (cmd) => cmd.creator_id?.trim() === normalizedCreatorUserId,
@@ -344,9 +366,9 @@ export async function registerSlashCommands(params: {
           trigger: spec.trigger,
           method: MATTERMOST_SLASH_POST_METHOD,
           url: callbackUrl,
-          description: spec.description,
+          description,
           auto_complete: spec.autoComplete,
-          auto_complete_desc: spec.description,
+          auto_complete_desc: description,
           auto_complete_hint: spec.autoCompleteHint,
         });
         registered.push({
@@ -383,9 +405,9 @@ export async function registerSlashCommands(params: {
         trigger: spec.trigger,
         method: MATTERMOST_SLASH_POST_METHOD,
         url: callbackUrl,
-        description: spec.description,
+        description,
         auto_complete: spec.autoComplete,
-        auto_complete_desc: spec.description,
+        auto_complete_desc: description,
         auto_complete_hint: spec.autoCompleteHint,
       });
       log?.(`mattermost: registered command /${spec.trigger} (id=${created.id})`);