fix(email): decode MIME alternatives without duplicating bodies (#6953)

src/email_mime.py

@@ -0,0 +1,13 @@
+"""Shared MIME text decoding for the web email helpers and MCP server."""
+
+
+def decode_text_part(part) -> str:
+    payload = part.get_payload(decode=True)
+    if not payload:
+        return ""
+    charset = part.get_content_charset() or "utf-8"
+    try:
+        return payload.decode(charset, errors="replace")
+    except (LookupError, ValueError):
+        # Broken senders can label valid UTF-8 with an unsupported codec.
+        return payload.decode("utf-8", errors="replace")