diff --git a/extensions/msteams/src/attachments/shared.ts b/extensions/msteams/src/attachments/shared.ts
index 1a9e839f71b..533ecf197bf 100644
--- a/extensions/msteams/src/attachments/shared.ts
+++ b/extensions/msteams/src/attachments/shared.ts
@@ -1,7 +1,5 @@
 import { Buffer } from "node:buffer";
 import { lookup } from "node:dns/promises";
-export { estimateBase64DecodedBytes } from "openclaw/plugin-sdk/media-runtime";
-import { estimateBase64DecodedBytes } from "openclaw/plugin-sdk/media-runtime";
 import {
   buildHostnameAllowlistPolicyFromSuffixAllowlist,
   isHttpsUrlAllowedByHostnameSuffixAllowlist,
@@ -84,6 +82,42 @@ export const DEFAULT_MEDIA_AUTH_HOST_ALLOWLIST = [
 export const GRAPH_ROOT = "https://graph.microsoft.com/v1.0";
 export { isRecord };
 
+// Keep this local; importing the broad media-runtime SDK barrel pulls image/audio runtimes into
+// hot MSTeams attachment tests for one tiny estimator.
+export function estimateBase64DecodedBytes(base64: string): number {
+  let effectiveLen = 0;
+  for (let i = 0; i < base64.length; i += 1) {
+    const code = base64.charCodeAt(i);
+    if (code <= 0x20) {
+      continue;
+    }
+    effectiveLen += 1;
+  }
+
+  if (effectiveLen === 0) {
+    return 0;
+  }
+
+  let padding = 0;
+  let end = base64.length - 1;
+  while (end >= 0 && base64.charCodeAt(end) <= 0x20) {
+    end -= 1;
+  }
+  if (end >= 0 && base64[end] === "=") {
+    padding = 1;
+    end -= 1;
+    while (end >= 0 && base64.charCodeAt(end) <= 0x20) {
+      end -= 1;
+    }
+    if (end >= 0 && base64[end] === "=") {
+      padding = 2;
+    }
+  }
+
+  const estimated = Math.floor((effectiveLen * 3) / 4) - padding;
+  return Math.max(0, estimated);
+}
+
 /**
  * Host suffixes for SharePoint/OneDrive shared links that must be fetched via
  * the Graph `/shares/{shareId}/driveItem/content` endpoint instead of directly.