diff --git a/extensions/msteams/src/attachments/graph.ts b/extensions/msteams/src/attachments/graph.ts
index 221a32fff69..cf346b03615 100644
--- a/extensions/msteams/src/attachments/graph.ts
+++ b/extensions/msteams/src/attachments/graph.ts
@@ -1,3 +1,7 @@
+import {
+  normalizeLowercaseStringOrEmpty,
+  normalizeOptionalLowercaseString,
+} from "openclaw/plugin-sdk/text-runtime";
 import { fetchWithSsrFGuard, type SsrFPolicy } from "../../runtime-api.js";
 import { getMSTeamsRuntime } from "../runtime.js";
 import { ensureUserAgentHeader } from "../user-agent.js";
@@ -46,7 +50,7 @@ export function buildMSTeamsGraphMessageUrls(params: {
   conversationMessageId?: string | null;
   channelData?: unknown;
 }): string[] {
-  const conversationType = params.conversationType?.trim().toLowerCase() ?? "";
+  const conversationType = normalizeLowercaseStringOrEmpty(params.conversationType ?? "");
   const messageIdCandidates = new Set<string>();
   const pushCandidate = (value: string | null | undefined) => {
     const trimmed = typeof value === "string" ? value.trim() : "";
@@ -382,7 +386,7 @@ export async function downloadMSTeamsGraphMedia(params: {
   const filteredAttachments =
     sharePointMedia.length > 0
       ? normalizedAttachments.filter((att) => {
-          const contentType = att.contentType?.toLowerCase();
+          const contentType = normalizeOptionalLowercaseString(att.contentType);
           if (contentType !== "reference") {
             return true;
           }
diff --git a/extensions/msteams/src/attachments/shared.ts b/extensions/msteams/src/attachments/shared.ts
index 7aa257c16a4..c8d1ec288b7 100644
--- a/extensions/msteams/src/attachments/shared.ts
+++ b/extensions/msteams/src/attachments/shared.ts
@@ -7,7 +7,11 @@ import {
   normalizeHostnameSuffixAllowlist,
   type SsrFPolicy,
 } from "openclaw/plugin-sdk/ssrf-policy";
-import { isRecord, normalizeOptionalString } from "openclaw/plugin-sdk/text-runtime";
+import {
+  isRecord,
+  normalizeLowercaseStringOrEmpty,
+  normalizeOptionalString,
+} from "openclaw/plugin-sdk/text-runtime";
 import type { MSTeamsAttachmentLike } from "./types.js";
 
 type InlineImageCandidate =
@@ -119,9 +123,9 @@ export function inferPlaceholder(params: {
   fileName?: string;
   fileType?: string;
 }): string {
-  const mime = params.contentType?.toLowerCase() ?? "";
-  const name = params.fileName?.toLowerCase() ?? "";
-  const fileType = params.fileType?.toLowerCase() ?? "";
+  const mime = normalizeLowercaseStringOrEmpty(params.contentType ?? "");
+  const name = normalizeLowercaseStringOrEmpty(params.fileName ?? "");
+  const fileType = normalizeLowercaseStringOrEmpty(params.fileType ?? "");
 
   const looksLikeImage =
     mime.startsWith("image/") || IMAGE_EXT_RE.test(name) || IMAGE_EXT_RE.test(`x.${fileType}`);
@@ -232,7 +236,7 @@ function decodeDataImageWithLimits(
   if (!match) {
     return { candidate: null, estimatedBytes: 0 };
   }
-  const contentType = match[1]?.toLowerCase();
+  const contentType = normalizeLowercaseStringOrEmpty(match[1] ?? "");
   const isBase64 = Boolean(match[2]);
   if (!isBase64) {
     return { candidate: null, estimatedBytes: 0 };
diff --git a/extensions/msteams/src/feedback-reflection.ts b/extensions/msteams/src/feedback-reflection.ts
index 6e3ce78fae3..605ae402e18 100644
--- a/extensions/msteams/src/feedback-reflection.ts
+++ b/extensions/msteams/src/feedback-reflection.ts
@@ -10,6 +10,7 @@
  * 6. Optionally sends a proactive follow-up to the user
  */
 
+import { normalizeOptionalLowercaseString } from "openclaw/plugin-sdk/text-runtime";
 import {
   dispatchReplyFromConfigWithSettledDispatcher,
   type OpenClawConfig,
@@ -241,7 +242,9 @@ export async function runFeedbackReflection(params: RunFeedbackReflectionParams)
     log.debug?.("failed to store reflection learning", { error: formatUnknownError(err) });
   }
 
-  const conversationType = params.conversationRef.conversation?.conversationType?.toLowerCase();
+  const conversationType = normalizeOptionalLowercaseString(
+    params.conversationRef.conversation?.conversationType,
+  );
   const shouldNotify =
     conversationType === "personal" &&
     parsedReflection.followUp &&
diff --git a/extensions/msteams/src/file-consent-helpers.ts b/extensions/msteams/src/file-consent-helpers.ts
index e8a1bc0c696..2c9a7f932de 100644
--- a/extensions/msteams/src/file-consent-helpers.ts
+++ b/extensions/msteams/src/file-consent-helpers.ts
@@ -9,6 +9,7 @@
  * and messenger.ts (reply path) to avoid duplication.
  */
 
+import { normalizeOptionalLowercaseString } from "openclaw/plugin-sdk/text-runtime";
 import { buildFileConsentCard } from "./file-consent.js";
 import { storePendingUpload } from "./pending-uploads.js";
 
@@ -66,7 +67,7 @@ export function requiresFileConsent(params: {
   bufferSize: number;
   thresholdBytes: number;
 }): boolean {
-  const isPersonal = params.conversationType?.toLowerCase() === "personal";
+  const isPersonal = normalizeOptionalLowercaseString(params.conversationType) === "personal";
   const isImage = params.contentType?.startsWith("image/") ?? false;
   const isLargeFile = params.bufferSize >= params.thresholdBytes;
   return isPersonal && (isLargeFile || !isImage);
diff --git a/extensions/msteams/src/reply-dispatcher.ts b/extensions/msteams/src/reply-dispatcher.ts
index a1b0ca3d0d3..4ada78aab78 100644
--- a/extensions/msteams/src/reply-dispatcher.ts
+++ b/extensions/msteams/src/reply-dispatcher.ts
@@ -1,3 +1,4 @@
+import { normalizeOptionalLowercaseString } from "openclaw/plugin-sdk/text-runtime";
 import {
   createChannelReplyPipeline,
   logTypingFailure,
@@ -47,7 +48,9 @@ export function createMSTeamsReplyDispatcher(params: {
 }) {
   const core = getMSTeamsRuntime();
   const msteamsCfg = params.cfg.channels?.msteams;
-  const conversationType = params.conversationRef.conversation?.conversationType?.toLowerCase();
+  const conversationType = normalizeOptionalLowercaseString(
+    params.conversationRef.conversation?.conversationType,
+  );
   const isTypingSupported = conversationType === "personal" || conversationType === "groupchat";
 
   const sendTypingIndicator = isTypingSupported
diff --git a/extensions/msteams/src/reply-stream-controller.ts b/extensions/msteams/src/reply-stream-controller.ts
index 4539f6a5ae3..13494feab34 100644
--- a/extensions/msteams/src/reply-stream-controller.ts
+++ b/extensions/msteams/src/reply-stream-controller.ts
@@ -1,3 +1,4 @@
+import { normalizeOptionalLowercaseString } from "openclaw/plugin-sdk/text-runtime";
 import type { ReplyPayload } from "../runtime-api.js";
 import { formatUnknownError } from "./errors.js";
 import type { MSTeamsMonitorLogger } from "./monitor-types.js";
@@ -23,7 +24,7 @@ export function createTeamsReplyStreamController(params: {
   log: MSTeamsMonitorLogger;
   random?: () => number;
 }) {
-  const isPersonal = params.conversationType?.toLowerCase() === "personal";
+  const isPersonal = normalizeOptionalLowercaseString(params.conversationType) === "personal";
   const stream = isPersonal
     ? new TeamsHttpStream({
         sendActivity: (activity) => params.context.sendActivity(activity),
diff --git a/extensions/msteams/src/resolve-allowlist.ts b/extensions/msteams/src/resolve-allowlist.ts
index a5145bebf0f..f195130e141 100644
--- a/extensions/msteams/src/resolve-allowlist.ts
+++ b/extensions/msteams/src/resolve-allowlist.ts
@@ -1,4 +1,8 @@
 import { mapAllowlistResolutionInputs } from "openclaw/plugin-sdk/allow-from";
+import {
+  normalizeLowercaseStringOrEmpty,
+  normalizeOptionalLowercaseString,
+} from "openclaw/plugin-sdk/text-runtime";
 import { searchGraphUsers } from "./graph-users.js";
 import {
   listChannelsForTeam,
@@ -135,7 +139,9 @@ export async function resolveMSTeamsChannelAllowlist(params: {
       } catch {
         // API failure (rate limit, network error) — fall back to Graph GUID as team key
       }
-      const generalChannel = teamChannels.find((ch) => ch.displayName?.toLowerCase() === "general");
+      const generalChannel = teamChannels.find(
+        (ch) => normalizeOptionalLowercaseString(ch.displayName) === "general",
+      );
       // Use the General channel's conversation ID as the team key — this
       // matches what Bot Framework sends at runtime. Fall back to the Graph
       // GUID if the General channel isn't found (renamed or deleted).
@@ -150,11 +156,14 @@ export async function resolveMSTeamsChannelAllowlist(params: {
         };
       }
       // Reuse teamChannels — already fetched above
+      const normalizedChannel = normalizeOptionalLowercaseString(channel);
       const channelMatch =
         teamChannels.find((item) => item.id === channel) ??
-        teamChannels.find((item) => item.displayName?.toLowerCase() === channel.toLowerCase()) ??
+        teamChannels.find(
+          (item) => normalizeOptionalLowercaseString(item.displayName) === normalizedChannel,
+        ) ??
         teamChannels.find((item) =>
-          item.displayName?.toLowerCase().includes(channel.toLowerCase() ?? ""),
+          normalizeLowercaseStringOrEmpty(item.displayName ?? "").includes(normalizedChannel ?? ""),
         );
       if (!channelMatch?.id) {
         return { input, resolved: false, note: "channel not found" };
diff --git a/extensions/msteams/src/session-route.ts b/extensions/msteams/src/session-route.ts
index 95f778b0249..11700878ebd 100644
--- a/extensions/msteams/src/session-route.ts
+++ b/extensions/msteams/src/session-route.ts
@@ -4,6 +4,7 @@ import {
   stripTargetKindPrefix,
   type ChannelOutboundSessionRouteParams,
 } from "openclaw/plugin-sdk/core";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 
 export function resolveMSTeamsOutboundSessionRoute(params: ChannelOutboundSessionRouteParams) {
   let trimmed = stripChannelTargetPrefix(params.target, "msteams", "teams");
@@ -11,7 +12,7 @@ export function resolveMSTeamsOutboundSessionRoute(params: ChannelOutboundSessio
     return null;
   }
 
-  const lower = trimmed.toLowerCase();
+  const lower = normalizeLowercaseStringOrEmpty(trimmed);
   const isUser = lower.startsWith("user:");
   const rawId = stripTargetKindPrefix(trimmed);
   if (!rawId) {