diff --git a/AGENTS.md b/AGENTS.md
index b9b3938..0213852 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -10,7 +10,7 @@
 - `cmake --build --preset debug` compiles the program and tests.
 - `./build/debug/wibo /path/to/program.exe` runs a Windows binary. Use `-D` (or `WIBO_DEBUG=1`) for verbose logging. Use `-C` to set the working directory.
 - `ctest --preset fixtures` runs the self-checking WinAPI fixtures (requires `i686-w64-mingw32-gcc` and `i686-w64-mingw32-windres`).
-- `clang-format -i path/to/file.cpp` and `clang-tidy path/to/file.cpp -p build` keep contributions aligned with the repo's tooling.
+- `clang-format -i path/to/file.cpp` and `clang-tidy -p build/debug path/to/file.cpp` keep contributions aligned with the repo's tooling.
 
 ## Coding Style & Naming Conventions
 - Formatting follows `.clang-format` (LLVM base, tabbed indentation width 4, 120 column limit).
diff --git a/dll/kernel32/debugapi.cpp b/dll/kernel32/debugapi.cpp
index 4abaed3..d0f7b61 100644
--- a/dll/kernel32/debugapi.cpp
+++ b/dll/kernel32/debugapi.cpp
@@ -2,7 +2,6 @@
 
 #include "common.h"
 #include "context.h"
-#include "errors.h"
 
 namespace kernel32 {
 
diff --git a/dll/kernel32/internal.h b/dll/kernel32/internal.h
index 46ecc68..2d4fd77 100644
--- a/dll/kernel32/internal.h
+++ b/dll/kernel32/internal.h
@@ -55,7 +55,7 @@ struct ProcessObject final : WaitableObject {
 	static constexpr ObjectType kType = ObjectType::Process;
 
 	pid_t pid;
-	pid_t tid;
+	pid_t tid = 0;
 	int pidfd;
 	DWORD exitCode = STILL_ACTIVE;
 	bool forcedExitCode = false;
diff --git a/dll/kernel32/winnls.cpp b/dll/kernel32/winnls.cpp
index 8b70f34..8baf3f7 100644
--- a/dll/kernel32/winnls.cpp
+++ b/dll/kernel32/winnls.cpp
@@ -315,9 +315,9 @@ int WIN_FUNC LCMapStringW(LCID Locale, DWORD dwMapFlags, LPCWCH lpSrcStr, int cc
 	for (size_t i = 0; i < srcLen; ++i) {
 		uint16_t ch = lpSrcStr[i];
 		if (casingFlags == 0x00000200u) {
-			buffer[i] = static_cast<uint16_t>(std::towupper(static_cast<wint_t>(ch)));
+			buffer[i] = wcharToUpper(ch);
 		} else if (casingFlags == 0x00000100u) {
-			buffer[i] = static_cast<uint16_t>(std::towlower(static_cast<wint_t>(ch)));
+			buffer[i] = wcharToLower(ch);
 		} else {
 			buffer[i] = ch;
 		}
diff --git a/dll/msvcrt.cpp b/dll/msvcrt.cpp
index c324bb6..f464a2f 100644
--- a/dll/msvcrt.cpp
+++ b/dll/msvcrt.cpp
@@ -1613,13 +1613,13 @@ namespace msvcrt {
 	int WIN_ENTRY strcmp(const char *lhs, const char *rhs) {
 		HOST_CONTEXT_GUARD();
 		VERBOSE_LOG("strcmp(%s, %s)\n", lhs, rhs);
-		return ::strcmp(lhs, rhs); 
+		return ::strcmp(lhs, rhs);
 	}
 
 	int WIN_ENTRY strncmp(const char *lhs, const char *rhs, size_t count) {
 		HOST_CONTEXT_GUARD();
 		VERBOSE_LOG("strncmp(%s, %s, %zu)\n", lhs, rhs, count);
-		return ::strncmp(lhs, rhs, count); 
+		return ::strncmp(lhs, rhs, count);
 	}
 
 	void WIN_ENTRY _exit(int status) {
@@ -2150,8 +2150,7 @@ namespace msvcrt {
 			return ERANGE;
 		}
 		for (size_t i = 0; i < len; ++i) {
-			wchar_t ch = static_cast<wchar_t>(str[i]);
-			str[i] = static_cast<uint16_t>(std::towupper(ch));
+			str[i] = wcharToUpper(str[i]);
 		}
 		return 0;
 	}
@@ -2167,8 +2166,7 @@ namespace msvcrt {
 			return ERANGE;
 		}
 		for (size_t i = 0; i < len; ++i) {
-			wchar_t ch = static_cast<wchar_t>(str[i]);
-			str[i] = static_cast<uint16_t>(std::towlower(ch));
+			str[i] = wcharToLower(str[i]);
 		}
 		return 0;
 	}
@@ -2176,7 +2174,7 @@ namespace msvcrt {
 	wint_t WIN_ENTRY towlower(wint_t ch) {
 		HOST_CONTEXT_GUARD();
 		VERBOSE_LOG("towlower(%d)\n", ch);
-		return static_cast<wint_t>(std::towlower(static_cast<wchar_t>(ch)));
+		return wcharToLower(ch);
 	}
 
 	unsigned int WIN_ENTRY _mbctolower(unsigned int ch) {
@@ -2416,9 +2414,8 @@ namespace msvcrt {
 		}
 
 		const auto wStr = stringToWideString(wibo::guestExecutablePath.c_str());
-		if (_wpgmptr) {
-			delete[] _wpgmptr;
-		}
+		delete[] _wpgmptr;
+
 		_wpgmptr = new uint16_t[wStr.size() + 1];
 		std::copy(wStr.begin(), wStr.end(), _wpgmptr);
 		_wpgmptr[wStr.size()] = 0;
@@ -2660,7 +2657,7 @@ namespace msvcrt {
 		return 0;
 	}
 
-	int WIN_ENTRY wcscpy_s(uint16_t *dest, size_t dest_size, const uint16_t *src){
+	int WIN_ENTRY wcscpy_s(uint16_t *dest, size_t dest_size, const uint16_t *src) {
 		HOST_CONTEXT_GUARD();
 		std::string src_str = wideStringToString(src);
 		VERBOSE_LOG("wcscpy_s(%p, %zu, %p)\n", dest, dest_size, src);
@@ -2670,7 +2667,7 @@ namespace msvcrt {
 
 		if (wstrlen(src) + 1 > dest_size) {
 			dest[0] = 0;
-			return 34; 
+			return 34;
 		}
 
 		wstrcpy(dest, src);
@@ -2753,37 +2750,60 @@ namespace msvcrt {
 		return wstrncmp(string1, string2, count);
 	}
 
-	int WIN_ENTRY _vswprintf_c_l(uint16_t* buffer, size_t size, const uint16_t* format, ...) {
+	int WIN_ENTRY _vswprintf_c_l(uint16_t *buffer, size_t size, const uint16_t *format, ...) {
 		HOST_CONTEXT_GUARD();
 		DEBUG_LOG("_vswprintf_c_l(%p, %zu, %p, ...)\n", buffer, size, format);
-		if (!buffer || !format || size == 0)
+		if (!buffer || !format || size == 0) {
+			if (buffer && size > 0) {
+				buffer[0] = 0;
+			}
 			return -1;
+		}
 
 		std::string narrow_fmt = wideStringToString(format);
 		DEBUG_LOG("\tFmt: %s\n", narrow_fmt.c_str());
-		
+
 		va_list args;
 		va_start(args, format);
-		int required = vsnprintf(nullptr, 0, narrow_fmt.c_str(), args);
-		va_end(args);
+		va_list argsCopy;
+		va_copy(argsCopy, args);
+		int required = vsnprintf(nullptr, 0, narrow_fmt.c_str(), argsCopy);
+		va_end(argsCopy);
+
 		if (required < 0) {
+			va_end(args);
 			buffer[0] = 0;
 			return -1;
 		}
 
-		char buffer_narrow[required + 1];
-		va_start(args, format);
-		vsnprintf(buffer_narrow, required + 1, narrow_fmt.c_str(), args);
+		std::vector<char> narrowBuffer(static_cast<size_t>(required) + 1);
+		int written = vsnprintf(narrowBuffer.data(), narrowBuffer.size(), narrow_fmt.c_str(), args);
 		va_end(args);
-		DEBUG_LOG("\tBuffer: %s\n", buffer_narrow);
 
-		std::vector<uint16_t> wide = stringToWideString(buffer_narrow);
-		size_t copy_len = std::min(wide.size(), size - 1);
-		std::memcpy(buffer, wide.data(), copy_len * sizeof(uint16_t));
-		buffer[copy_len] = 0;
+		if (written < 0) {
+			buffer[0] = 0;
+			return -1;
+		}
+		DEBUG_LOG("\tBuffer: %s\n", narrowBuffer.data());
 
-		return static_cast<int>(copy_len);
-		// return vswprintf(buffer, size, format, args); this doesn't work because on this architecture, wchar_t is size 4, instead of size 2
+		std::vector<uint16_t> wide = stringToWideString(narrowBuffer.data());
+		size_t wideLen = wide.size();
+
+		if (wideLen + 1 > size) {
+			buffer[0] = 0;
+			return -1;
+		}
+		if (wideLen > static_cast<size_t>(std::numeric_limits<int>::max())) {
+			buffer[0] = 0;
+			return -1;
+		}
+
+		if (wideLen > 0) {
+			std::memcpy(buffer, wide.data(), wideLen * sizeof(uint16_t));
+		}
+		buffer[wideLen] = 0;
+
+		return static_cast<int>(wideLen);
 	}
 
 	const uint16_t* WIN_ENTRY wcsstr( const uint16_t *dest, const uint16_t *src ){
diff --git a/dll/ntdll.cpp b/dll/ntdll.cpp
index a485ad1..ee2d2e7 100644
--- a/dll/ntdll.cpp
+++ b/dll/ntdll.cpp
@@ -14,7 +14,7 @@
 
 #include <optional>
 
-#define PIO_APC_ROUTINE void *
+using PIO_APC_ROUTINE = void *;
 
 typedef struct _IO_STATUS_BLOCK {
 	union {
@@ -109,7 +109,7 @@ std::string windowsImagePathFor(const ProcessHandleDetails &details) {
 	if (!ec) {
 		return files::pathToWindows(files::canonicalPath(resolved));
 	}
-	return std::string();
+	return {};
 }
 
 } // namespace
diff --git a/dll/version.cpp b/dll/version.cpp
index d90c78d..57034d5 100644
--- a/dll/version.cpp
+++ b/dll/version.cpp
@@ -16,11 +16,11 @@ namespace {
 
 constexpr uint32_t RT_VERSION = 16;
 
-static uint16_t readU16(const uint8_t *ptr) { return static_cast<uint16_t>(ptr[0] | (ptr[1] << 8)); }
+uint16_t readU16(const uint8_t *ptr) { return static_cast<uint16_t>(ptr[0] | (ptr[1] << 8)); }
 
-static size_t align4(size_t offset) { return (offset + 3u) & ~static_cast<size_t>(3u); }
+size_t align4(size_t offset) { return (offset + 3u) & ~static_cast<size_t>(3u); }
 
-static std::string narrowKey(const std::u16string &key) {
+std::string narrowKey(const std::u16string &key) {
 	std::string result;
 	result.reserve(key.size());
 	for (char16_t ch : key) {
@@ -40,7 +40,7 @@ struct VersionBlockView {
 	uint32_t childrenBytes = 0;
 };
 
-static bool parseVersionBlock(const uint8_t *block, size_t available, VersionBlockView &out) {
+bool parseVersionBlock(const uint8_t *block, size_t available, VersionBlockView &out) {
 	if (available < sizeof(uint16_t) * 3) {
 		DEBUG_LOG("header too small: available=%zu\n", available);
 		return false;
@@ -99,8 +99,8 @@ static bool parseVersionBlock(const uint8_t *block, size_t available, VersionBlo
 	return true;
 }
 
-static bool queryVersionBlock(const uint8_t *block, size_t available, const std::vector<std::string> &segments,
-							  size_t depth, const uint8_t **outPtr, uint32_t *outLen, uint16_t *outType) {
+bool queryVersionBlock(const uint8_t *block, size_t available, const std::vector<std::string> &segments, size_t depth,
+					   const uint8_t **outPtr, uint32_t *outLen, uint16_t *outType) {
 	VersionBlockView view;
 	if (!parseVersionBlock(block, available, view))
 		return false;
@@ -139,7 +139,7 @@ static bool queryVersionBlock(const uint8_t *block, size_t available, const std:
 	return false;
 }
 
-static bool splitSubBlock(const std::string &subBlock, std::vector<std::string> &segments) {
+bool splitSubBlock(const std::string &subBlock, std::vector<std::string> &segments) {
 	segments.clear();
 	if (subBlock.empty() || subBlock == "\\")
 		return true;
@@ -158,7 +158,7 @@ static bool splitSubBlock(const std::string &subBlock, std::vector<std::string>
 	return true;
 }
 
-static bool loadVersionResource(const char *fileName, std::vector<uint8_t> &buffer) {
+bool loadVersionResource(const char *fileName, std::vector<uint8_t> &buffer) {
 	if (!fileName) {
 		wibo::lastError = ERROR_INVALID_PARAMETER;
 		return false;
diff --git a/src/strutil.cpp b/src/strutil.cpp
index 40a619b..bbb1426 100644
--- a/src/strutil.cpp
+++ b/src/strutil.cpp
@@ -36,14 +36,26 @@ uint16_t wcharToLower(uint16_t ch) {
 	if (ch >= 'A' && ch <= 'Z') {
 		return static_cast<uint16_t>(ch + ('a' - 'A'));
 	}
-	wchar_t wide = static_cast<wchar_t>(ch);
-	wchar_t lowered = std::towlower(wide);
-	if (lowered < 0 || lowered > 0xFFFF) {
+	wint_t wide = static_cast<wint_t>(ch);
+	wint_t lowered = std::towlower(wide);
+	if (lowered > 0xFFFF) {
 		return ch;
 	}
 	return static_cast<uint16_t>(lowered);
 }
 
+uint16_t wcharToUpper(uint16_t ch) {
+	if (ch >= 'a' && ch <= 'z') {
+		return static_cast<uint16_t>(ch - ('a' - 'A'));
+	}
+	wint_t wide = static_cast<wint_t>(ch);
+	wint_t uppered = std::towupper(wide);
+	if (uppered > 0xFFFF) {
+		return ch;
+	}
+	return static_cast<uint16_t>(uppered);
+}
+
 size_t wstrlen(const uint16_t *str) {
 	if (!str)
 		return 0;
diff --git a/src/strutil.h b/src/strutil.h
index 43f1446..bc90bb9 100644
--- a/src/strutil.h
+++ b/src/strutil.h
@@ -24,3 +24,4 @@ void toUpperInPlace(std::string &str);
 std::string stringToLower(std::string_view str);
 std::string stringToUpper(std::string_view str);
 uint16_t wcharToLower(uint16_t ch);
+uint16_t wcharToUpper(uint16_t ch);