diff --git a/extensions/signal/src/channel.ts b/extensions/signal/src/channel.ts
index 9144c68fb18..be5c8f9dae9 100644
--- a/extensions/signal/src/channel.ts
+++ b/extensions/signal/src/channel.ts
@@ -18,6 +18,7 @@ import {
   createComputedAccountStatusAdapter,
   createDefaultChannelRuntimeState,
 } from "openclaw/plugin-sdk/status-helpers";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import { resolveSignalAccount, type ResolvedSignalAccount } from "./accounts.js";
 import { signalApprovalAuth } from "./approval-auth.js";
 import { markdownToSignalTextChunks } from "./format.js";
@@ -103,7 +104,7 @@ function inferSignalTargetChatType(rawTo: string) {
   if (!to) {
     return undefined;
   }
-  const lower = to.toLowerCase();
+  const lower = normalizeLowercaseStringOrEmpty(to);
   if (lower.startsWith("group:")) {
     return "group" as const;
   }
diff --git a/extensions/signal/src/format.ts b/extensions/signal/src/format.ts
index b8d559fc012..66539548731 100644
--- a/extensions/signal/src/format.ts
+++ b/extensions/signal/src/format.ts
@@ -1,6 +1,7 @@
 import type { MarkdownTableMode } from "openclaw/plugin-sdk/config-runtime";
 import {
   markdownToIR,
+  normalizeLowercaseStringOrEmpty,
   type MarkdownIR,
   type MarkdownStyle,
   renderMarkdownIRChunksWithinLimit,
@@ -35,7 +36,7 @@ type Insertion = {
 };
 
 function normalizeUrlForComparison(url: string): string {
-  let normalized = url.toLowerCase();
+  let normalized = normalizeLowercaseStringOrEmpty(url);
   // Strip protocol
   normalized = normalized.replace(/^https?:\/\//, "");
   // Strip www. prefix
diff --git a/extensions/signal/src/identity.ts b/extensions/signal/src/identity.ts
index 4375e79e0c4..987c19bf118 100644
--- a/extensions/signal/src/identity.ts
+++ b/extensions/signal/src/identity.ts
@@ -1,5 +1,5 @@
 import { evaluateSenderGroupAccessForPolicy } from "openclaw/plugin-sdk/group-access";
-import { normalizeE164 } from "openclaw/plugin-sdk/text-runtime";
+import { normalizeE164, normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import { looksLikeUuid } from "./uuid.js";
 
 export type SignalSender =
@@ -69,7 +69,7 @@ function parseSignalAllowEntry(entry: string): SignalAllowEntry | null {
   }
 
   const stripped = stripSignalPrefix(trimmed);
-  const lower = stripped.toLowerCase();
+  const lower = normalizeLowercaseStringOrEmpty(stripped);
   if (lower.startsWith("uuid:")) {
     const raw = stripped.slice("uuid:".length).trim();
     if (!raw) {
diff --git a/extensions/signal/src/install-signal-cli.ts b/extensions/signal/src/install-signal-cli.ts
index fbbc5908a34..d7bc0a3ec49 100644
--- a/extensions/signal/src/install-signal-cli.ts
+++ b/extensions/signal/src/install-signal-cli.ts
@@ -8,6 +8,7 @@ import { formatErrorMessage } from "openclaw/plugin-sdk/error-runtime";
 import { runPluginCommandWithTimeout } from "openclaw/plugin-sdk/run-command";
 import type { RuntimeEnv } from "openclaw/plugin-sdk/runtime-env";
 import { CONFIG_DIR, extractArchive, resolveBrewExecutable } from "openclaw/plugin-sdk/setup-tools";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 
 export type ReleaseAsset = {
   name?: string;
@@ -64,10 +65,12 @@ export function pickAsset(
   );
 
   // Archives only, excluding signature files (.asc)
-  const archives = withName.filter((a) => looksLikeArchive(a.name.toLowerCase()));
+  const archives = withName.filter((a) =>
+    looksLikeArchive(normalizeLowercaseStringOrEmpty(a.name)),
+  );
 
   const byName = (pattern: RegExp) =>
-    archives.find((asset) => pattern.test(asset.name.toLowerCase()));
+    archives.find((asset) => pattern.test(normalizeLowercaseStringOrEmpty(asset.name)));
 
   if (platform === "linux") {
     // The official "Linux-native" asset is an x86-64 GraalVM binary.
@@ -253,7 +256,7 @@ async function installSignalCliFromRelease(runtime: RuntimeEnv): Promise<SignalI
   const installRoot = path.join(CONFIG_DIR, "tools", "signal-cli", version);
   await fs.mkdir(installRoot, { recursive: true });
 
-  if (!looksLikeArchive(asset.name.toLowerCase())) {
+  if (!looksLikeArchive(normalizeLowercaseStringOrEmpty(asset.name))) {
     return { ok: false, error: `Unsupported archive type: ${asset.name}` };
   }
   try {
diff --git a/extensions/signal/src/message-actions.ts b/extensions/signal/src/message-actions.ts
index 8c819c45f4d..162089e6324 100644
--- a/extensions/signal/src/message-actions.ts
+++ b/extensions/signal/src/message-actions.ts
@@ -4,6 +4,7 @@ import type {
   ChannelMessageActionAdapter,
   ChannelMessageActionName,
 } from "openclaw/plugin-sdk/channel-contract";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import { removeReactionSignal, sendReactionSignal } from "../reaction-runtime-api.js";
 import { listEnabledSignalAccounts, resolveSignalAccount } from "./accounts.js";
 import { resolveSignalReactionLevel } from "./reaction-level.js";
@@ -20,7 +21,7 @@ function normalizeSignalReactionRecipient(raw: string): string {
   if (!withoutSignal) {
     return withoutSignal;
   }
-  if (withoutSignal.toLowerCase().startsWith("uuid:")) {
+  if (normalizeLowercaseStringOrEmpty(withoutSignal).startsWith("uuid:")) {
     return withoutSignal.slice("uuid:".length).trim();
   }
   return withoutSignal;
@@ -35,7 +36,7 @@ function resolveSignalReactionTarget(raw: string): { recipient?: string; groupId
   if (!withoutSignal) {
     return {};
   }
-  if (withoutSignal.toLowerCase().startsWith(GROUP_PREFIX)) {
+  if (normalizeLowercaseStringOrEmpty(withoutSignal).startsWith(GROUP_PREFIX)) {
     const groupId = withoutSignal.slice(GROUP_PREFIX.length).trim();
     return groupId ? { groupId } : {};
   }
diff --git a/extensions/signal/src/normalize.ts b/extensions/signal/src/normalize.ts
index 0c2cb638aec..dd207c80377 100644
--- a/extensions/signal/src/normalize.ts
+++ b/extensions/signal/src/normalize.ts
@@ -1,33 +1,35 @@
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
+
 export function normalizeSignalMessagingTarget(raw: string): string | undefined {
   const trimmed = raw.trim();
   if (!trimmed) {
     return undefined;
   }
   let normalized = trimmed;
-  if (normalized.toLowerCase().startsWith("signal:")) {
+  if (normalizeLowercaseStringOrEmpty(normalized).startsWith("signal:")) {
     normalized = normalized.slice("signal:".length).trim();
   }
   if (!normalized) {
     return undefined;
   }
-  const lower = normalized.toLowerCase();
+  const lower = normalizeLowercaseStringOrEmpty(normalized);
   if (lower.startsWith("group:")) {
     const id = normalized.slice("group:".length).trim();
     return id ? `group:${id}` : undefined;
   }
   if (lower.startsWith("username:")) {
     const id = normalized.slice("username:".length).trim();
-    return id ? `username:${id}`.toLowerCase() : undefined;
+    return id ? normalizeLowercaseStringOrEmpty(`username:${id}`) : undefined;
   }
   if (lower.startsWith("u:")) {
     const id = normalized.slice("u:".length).trim();
-    return id ? `username:${id}`.toLowerCase() : undefined;
+    return id ? normalizeLowercaseStringOrEmpty(`username:${id}`) : undefined;
   }
   if (lower.startsWith("uuid:")) {
     const id = normalized.slice("uuid:".length).trim();
-    return id ? id.toLowerCase() : undefined;
+    return id ? normalizeLowercaseStringOrEmpty(id) : undefined;
   }
-  return normalized.toLowerCase();
+  return normalizeLowercaseStringOrEmpty(normalized);
 }
 
 const UUID_PATTERN = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;
diff --git a/extensions/signal/src/outbound-session.ts b/extensions/signal/src/outbound-session.ts
index 0b56664e27a..db6f00ad8f5 100644
--- a/extensions/signal/src/outbound-session.ts
+++ b/extensions/signal/src/outbound-session.ts
@@ -1,4 +1,5 @@
 import { type RoutePeer } from "openclaw/plugin-sdk/routing";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import { resolveSignalPeerId, resolveSignalRecipient, resolveSignalSender } from "./identity.js";
 import { looksLikeUuid } from "./uuid.js";
 
@@ -11,7 +12,7 @@ export type ResolvedSignalOutboundTarget = {
 
 export function resolveSignalOutboundTarget(target: string): ResolvedSignalOutboundTarget | null {
   const stripped = target.replace(/^signal:/i, "").trim();
-  const lowered = stripped.toLowerCase();
+  const lowered = normalizeLowercaseStringOrEmpty(stripped);
   if (lowered.startsWith("group:")) {
     const groupId = stripped.slice("group:".length).trim();
     if (!groupId) {
@@ -35,7 +36,7 @@ export function resolveSignalOutboundTarget(target: string): ResolvedSignalOutbo
     return null;
   }
 
-  const uuidCandidate = recipient.toLowerCase().startsWith("uuid:")
+  const uuidCandidate = normalizeLowercaseStringOrEmpty(recipient).startsWith("uuid:")
     ? recipient.slice("uuid:".length)
     : recipient;
   const sender = resolveSignalSender({
diff --git a/extensions/signal/src/send-reactions.ts b/extensions/signal/src/send-reactions.ts
index 418cf913b58..6f3c00d6bf3 100644
--- a/extensions/signal/src/send-reactions.ts
+++ b/extensions/signal/src/send-reactions.ts
@@ -3,6 +3,7 @@
  */
 
 import type { OpenClawConfig } from "openclaw/plugin-sdk/config-runtime";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import { resolveSignalAccount } from "./accounts.js";
 import { signalRpcRequest } from "./client.js";
 import { resolveSignalRpcContext } from "./rpc-context.js";
@@ -52,7 +53,7 @@ function normalizeSignalUuid(raw: string): string {
   if (!trimmed) {
     return "";
   }
-  if (trimmed.toLowerCase().startsWith("uuid:")) {
+  if (normalizeLowercaseStringOrEmpty(trimmed).startsWith("uuid:")) {
     return trimmed.slice("uuid:".length).trim();
   }
   return trimmed;
diff --git a/extensions/signal/src/send.ts b/extensions/signal/src/send.ts
index b3a71c9061c..cb094e91efe 100644
--- a/extensions/signal/src/send.ts
+++ b/extensions/signal/src/send.ts
@@ -2,6 +2,7 @@ import { loadConfig, type OpenClawConfig } from "openclaw/plugin-sdk/config-runt
 import { resolveMarkdownTableMode } from "openclaw/plugin-sdk/config-runtime";
 import { kindFromMime } from "openclaw/plugin-sdk/media-runtime";
 import { resolveOutboundAttachmentFromUrl } from "openclaw/plugin-sdk/media-runtime";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import { resolveSignalAccount } from "./accounts.js";
 import { signalRpcRequest } from "./client.js";
 import { markdownToSignalText, type SignalTextStyleRange } from "./format.js";
@@ -66,11 +67,11 @@ function parseTarget(raw: string): SignalTarget {
   if (!value) {
     throw new Error("Signal recipient is required");
   }
-  const lower = value.toLowerCase();
+  const lower = normalizeLowercaseStringOrEmpty(value);
   if (lower.startsWith("signal:")) {
     value = value.slice("signal:".length).trim();
   }
-  const normalized = value.toLowerCase();
+  const normalized = normalizeLowercaseStringOrEmpty(value);
   if (normalized.startsWith("group:")) {
     return { type: "group", groupId: value.slice("group:".length).trim() };
   }
diff --git a/extensions/signal/src/setup-core.ts b/extensions/signal/src/setup-core.ts
index f7dbe039e98..4488e37bc47 100644
--- a/extensions/signal/src/setup-core.ts
+++ b/extensions/signal/src/setup-core.ts
@@ -18,7 +18,11 @@ import {
   type WizardPrompter,
 } from "openclaw/plugin-sdk/setup-runtime";
 import { formatCliCommand, formatDocsLink } from "openclaw/plugin-sdk/setup-tools";
-import { normalizeE164, normalizeOptionalString } from "openclaw/plugin-sdk/text-runtime";
+import {
+  normalizeE164,
+  normalizeLowercaseStringOrEmpty,
+  normalizeOptionalString,
+} from "openclaw/plugin-sdk/text-runtime";
 import { resolveDefaultSignalAccountId, resolveSignalAccount } from "./accounts.js";
 
 const channel = "signal" as const;
@@ -50,7 +54,7 @@ function isUuidLike(value: string): boolean {
 
 export function parseSignalAllowFromEntries(raw: string): { entries: string[]; error?: string } {
   return parseSetupEntriesAllowingWildcard(raw, (entry) => {
-    if (entry.toLowerCase().startsWith("uuid:")) {
+    if (normalizeLowercaseStringOrEmpty(entry).startsWith("uuid:")) {
       const id = entry.slice("uuid:".length).trim();
       if (!id) {
         return { error: "Invalid uuid entry" };