Add 32-bit disclaimer and fix MSVC x86 warnings

- Move 32-bit warning to top of README with strong disclaimer
- Add static_cast<size_t> to fix truncation warnings on 32-bit MSVC

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

diff --git a/README.md b/README.md
index 44b71f0..31934dc 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,9 @@
 > [!IMPORTANT]
 > This library uses 'blocking' socket I/O. If you are looking for a library with 'non-blocking' socket I/O, this is not the one that you want.
 
+> [!WARNING]
+> 32-bit platforms are **NOT supported**. Use at your own risk. The library may compile on 32-bit targets, but no security review has been conducted for 32-bit environments. Integer truncation and other 32-bit-specific issues may exist. **Security reports that only affect 32-bit platforms will be closed without action.** The maintainer does not have access to 32-bit environments for testing or fixing issues. CI includes basic compile checks only, not functional or security testing.
+
 ## Main Features
 
 - HTTP Server/Client
@@ -1545,11 +1548,6 @@
 > [!NOTE]
 > Windows 8 or lower, Visual Studio 2015 or lower, and Cygwin and MSYS2 including MinGW are neither supported nor tested.
 
-### 32-bit
-
-> [!NOTE]
-> 32-bit platforms are not officially supported, but should work for basic usage. CI includes build checks for 32-bit Windows (MSVC x86), Linux x86, and ARM 32-bit to catch regressions.
-
 ## License
 
 MIT license (© 2026 Yuji Hirose)

httplib.h

diff --git a/httplib.h b/httplib.h
index 935c812..7070416 100644
--- a/httplib.h
+++ b/httplib.h
@@ -2781,7 +2781,7 @@
   std::advance(it, static_cast<ssize_t>(id));
   if (it != rng.second) {
     if (is_numeric(it->second)) {
-      return std::strtoull(it->second.data(), nullptr, 10);
+      return static_cast<size_t>(std::strtoull(it->second.data(), nullptr, 10));
     } else {
       is_invalid_value = true;
     }
@@ -8221,7 +8221,8 @@
   assert(r.first <= r.second &&
          r.second < static_cast<ssize_t>(content_length));
   (void)(content_length);
-  return std::make_pair(r.first, static_cast<size_t>(r.second - r.first) + 1);
+  return std::make_pair(static_cast<size_t>(r.first),
+                        static_cast<size_t>(r.second - r.first) + 1);
 }
 
 inline std::string make_content_range_header_field(