ci, iwyu: Fix warnings in `src/util` and treat them as errors

diff --git a/ci/test/03_test_script.sh b/ci/test/03_test_script.sh
index 9d6351af..4e4d9757 100755
--- a/ci/test/03_test_script.sh
+++ b/ci/test/03_test_script.sh
@@ -209,7 +209,7 @@ fi
 
 if [[ "${RUN_IWYU}" == true ]]; then
   # TODO: Consider enforcing IWYU across the entire codebase.
-  FILES_WITH_ENFORCED_IWYU="/src/(((crypto|index|kernel|primitives|univalue/(lib|test)|zmq)/.*|common/license_info|node/blockstorage|node/utxo_snapshot|clientversion|core_io|signet)\\.cpp)"
+  FILES_WITH_ENFORCED_IWYU="/src/(((crypto|index|kernel|primitives|univalue/(lib|test)|util|zmq)/.*|common/license_info|node/blockstorage|node/utxo_snapshot|clientversion|core_io|signet)\\.cpp)"
   jq --arg patterns "$FILES_WITH_ENFORCED_IWYU" 'map(select(.file | test($patterns)))' "${BASE_BUILD_DIR}/compile_commands.json" > "${BASE_BUILD_DIR}/compile_commands_iwyu_errors.json"
   jq --arg patterns "$FILES_WITH_ENFORCED_IWYU" 'map(select(.file | test($patterns) | not))' "${BASE_BUILD_DIR}/compile_commands.json" > "${BASE_BUILD_DIR}/compile_commands_iwyu_warnings.json"
 
diff --git a/src/bench/strencodings.cpp b/src/bench/strencodings.cpp
index 7d4e1887..c00de181 100644
--- a/src/bench/strencodings.cpp
+++ b/src/bench/strencodings.cpp
@@ -4,6 +4,7 @@
 
 #include <bench/bench.h>
 #include <consensus/consensus.h>
+#include <crypto/hex_base.h>
 #include <random.h>
 #include <span.h>
 #include <util/strencodings.h>
diff --git a/src/logging.h b/src/logging.h
index 005c67fd..069a73ea 100644
--- a/src/logging.h
+++ b/src/logging.h
@@ -8,6 +8,7 @@
 
 #include <crypto/siphash.h>
 #include <logging/categories.h> // IWYU pragma: export
+#include <span.h>
 #include <util/fs.h>
 #include <util/log.h> // IWYU pragma: export
 #include <util/stdmutex.h>
diff --git a/src/uint256.h b/src/uint256.h
index d4204275..3fe44ab7 100644
--- a/src/uint256.h
+++ b/src/uint256.h
@@ -7,6 +7,7 @@
 #define BITCOIN_UINT256_H
 
 #include <crypto/common.h>
+#include <crypto/hex_base.h>
 #include <span.h>
 #include <util/strencodings.h>
 #include <util/string.h>
diff --git a/src/util/asmap.cpp b/src/util/asmap.cpp
index f8b5a527..04e47c24 100644
--- a/src/util/asmap.cpp
+++ b/src/util/asmap.cpp
@@ -4,20 +4,18 @@
 
 #include <util/asmap.h>
 
-#include <clientversion.h>
 #include <hash.h>
-#include <serialize.h>
 #include <streams.h>
 #include <uint256.h>
+#include <util/check.h>
 #include <util/fs.h>
 #include <util/log.h>
 
-#include <algorithm>
 #include <bit>
-#include <cassert>
 #include <cstddef>
 #include <cstdio>
 #include <span>
+#include <string>
 #include <utility>
 #include <vector>
 
diff --git a/src/util/bip32.cpp b/src/util/bip32.cpp
index db40bfb5..2488eacf 100644
--- a/src/util/bip32.cpp
+++ b/src/util/bip32.cpp
@@ -2,12 +2,14 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include <tinyformat.h>
 #include <util/bip32.h>
+
+#include <tinyformat.h>
 #include <util/strencodings.h>
 
 #include <cstdint>
 #include <cstdio>
+#include <optional>
 #include <sstream>
 
 bool ParseHDKeypath(const std::string& keypath_str, std::vector<uint32_t>& keypath)
diff --git a/src/util/bytevectorhash.cpp b/src/util/bytevectorhash.cpp
index 943517ad..40930301 100644
--- a/src/util/bytevectorhash.cpp
+++ b/src/util/bytevectorhash.cpp
@@ -2,10 +2,12 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <util/bytevectorhash.h>
+
 #include <crypto/siphash.h>
 #include <random.h>
-#include <util/bytevectorhash.h>
 
+#include <span>
 #include <vector>
 
 ByteVectorHash::ByteVectorHash() :
diff --git a/src/util/chaintype.cpp b/src/util/chaintype.cpp
index 5059ff7e..6029002a 100644
--- a/src/util/chaintype.cpp
+++ b/src/util/chaintype.cpp
@@ -4,7 +4,8 @@
 
 #include <util/chaintype.h>
 
-#include <cassert>
+#include <util/check.h>
+
 #include <optional>
 #include <string>
 
diff --git a/src/util/chaintype.h b/src/util/chaintype.h
index 3b246ea4..caae77c1 100644
--- a/src/util/chaintype.h
+++ b/src/util/chaintype.h
@@ -7,6 +7,7 @@
 
 #include <optional>
 #include <string>
+#include <string_view>
 
 enum class ChainType {
     MAIN,
diff --git a/src/util/check.h b/src/util/check.h
index 34801ca0..4f5b0010 100644
--- a/src/util/check.h
+++ b/src/util/check.h
@@ -8,11 +8,14 @@
 #include <attributes.h>
 
 #include <atomic>
+// We use `util/check.h` to provide the `assert()` macro
+// to ensure that `NDEBUG` is not defined.
 #include <cassert> // IWYU pragma: export
 #include <source_location>
 #include <stdexcept>
 #include <string>
 #include <string_view>
+#include <type_traits>
 #include <utility>
 
 constexpr bool G_FUZZING_BUILD{
diff --git a/src/util/exec.cpp b/src/util/exec.cpp
index 6b140613..87d11237 100644
--- a/src/util/exec.cpp
+++ b/src/util/exec.cpp
@@ -5,12 +5,17 @@
 #include <util/exec.h>
 
 #include <util/fs.h>
+#ifdef WIN32
 #include <util/subprocess.h>
+#endif
 
+#include <cstdlib>
 #include <string>
-#include <vector>
+#include <system_error>
 
 #ifdef WIN32
+#include <codecvt>
+#include <locale>
 #include <process.h>
 #include <windows.h>
 #else
diff --git a/src/util/expected.h b/src/util/expected.h
index 66fb98e0..c88c6de4 100644
--- a/src/util/expected.h
+++ b/src/util/expected.h
@@ -8,7 +8,6 @@
 #include <attributes.h>
 #include <util/check.h>
 
-#include <cassert>
 #include <exception>
 #include <utility>
 #include <variant>
diff --git a/src/util/feefrac.cpp b/src/util/feefrac.cpp
index 68ba2b66..088149be 100644
--- a/src/util/feefrac.cpp
+++ b/src/util/feefrac.cpp
@@ -3,9 +3,11 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <util/feefrac.h>
-#include <algorithm>
+
+#include <util/check.h>
+
 #include <array>
-#include <vector>
+#include <cstddef>
 
 std::partial_ordering CompareChunks(std::span<const FeeFrac> chunks0, std::span<const FeeFrac> chunks1)
 {
diff --git a/src/util/feefrac.h b/src/util/feefrac.h
index 25d87d34..30ec6b02 100644
--- a/src/util/feefrac.h
+++ b/src/util/feefrac.h
@@ -5,13 +5,13 @@
 #ifndef BITCOIN_UTIL_FEEFRAC_H
 #define BITCOIN_UTIL_FEEFRAC_H
 
-#include <span.h>
 #include <util/check.h>
 #include <util/overflow.h>
 
 #include <compare>
 #include <cstdint>
-#include <vector>
+#include <span>
+#include <utility>
 
 /** Data structure storing a fee and size, ordered by increasing fee/size.
  *
diff --git a/src/util/fs.cpp b/src/util/fs.cpp
index 692f6718..88966ab0 100644
--- a/src/util/fs.cpp
+++ b/src/util/fs.cpp
@@ -3,23 +3,21 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <util/fs.h>
+
+#include <util/check.h>
 #include <util/syserror.h>
 
+#include <cerrno>
+#include <string>
+
 #ifndef WIN32
-#include <cstring>
 #include <fcntl.h>
-#include <sys/file.h>
-#include <sys/utsname.h>
 #include <unistd.h>
 #else
 #include <limits>
 #include <windows.h>
 #endif
 
-#include <cassert>
-#include <cerrno>
-#include <string>
-
 namespace fsbridge {
 
 FILE *fopen(const fs::path& p, const char *mode)
diff --git a/src/util/fs.h b/src/util/fs.h
index dce371cc..73d69479 100644
--- a/src/util/fs.h
+++ b/src/util/fs.h
@@ -5,17 +5,18 @@
 #ifndef BITCOIN_UTIL_FS_H
 #define BITCOIN_UTIL_FS_H
 
-#include <tinyformat.h>
+// IWYU incorrectly suggests removing this header.
+// See https://github.com/include-what-you-use/include-what-you-use/issues/1931.
+#include <tinyformat.h> // IWYU pragma: keep
 
 #include <cstdio>
+// The `util/fs.h` header is designed to be a drop-in replacement for `filesystem`.
 #include <filesystem> // IWYU pragma: export
 #include <functional>
 #include <iomanip>
 #include <ios>
-#include <ostream>
 #include <string>
 #include <string_view>
-#include <system_error>
 #include <type_traits>
 #include <utility>
 
diff --git a/src/util/fs_helpers.cpp b/src/util/fs_helpers.cpp
index e7780d74..8e08e66d 100644
--- a/src/util/fs_helpers.cpp
+++ b/src/util/fs_helpers.cpp
@@ -24,6 +24,7 @@
 #ifndef WIN32
 #include <fcntl.h>
 #include <sys/resource.h>
+#include <sys/types.h>
 #include <unistd.h>
 #else
 #include <io.h>
diff --git a/src/util/fs_helpers.h b/src/util/fs_helpers.h
index d39ae115..face17fd 100644
--- a/src/util/fs_helpers.h
+++ b/src/util/fs_helpers.h
@@ -13,6 +13,7 @@
 #include <iosfwd>
 #include <limits>
 #include <optional>
+#include <string>
 
 #ifdef __APPLE__
 enum class FSType {
diff --git a/src/util/hasher.cpp b/src/util/hasher.cpp
index 3d5ffcf8..b12f7451 100644
--- a/src/util/hasher.cpp
+++ b/src/util/hasher.cpp
@@ -2,10 +2,10 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <util/hasher.h>
+
 #include <crypto/siphash.h>
 #include <random.h>
-#include <span.h>
-#include <util/hasher.h>
 
 SaltedUint256Hasher::SaltedUint256Hasher() : m_hasher{
     FastRandomContext().rand64(),
diff --git a/src/util/hasher.h b/src/util/hasher.h
index 02c77033..7e74c676 100644
--- a/src/util/hasher.h
+++ b/src/util/hasher.h
@@ -8,12 +8,11 @@
 #include <crypto/common.h>
 #include <crypto/siphash.h>
 #include <primitives/transaction.h>
-#include <span.h>
 #include <uint256.h>
 
-#include <concepts>
 #include <cstdint>
 #include <cstring>
+#include <span>
 
 class SaltedUint256Hasher
 {
diff --git a/src/util/obfuscation.h b/src/util/obfuscation.h
index e9a2e609..a5df75ec 100644
--- a/src/util/obfuscation.h
+++ b/src/util/obfuscation.h
@@ -5,7 +5,7 @@
 #ifndef BITCOIN_UTIL_OBFUSCATION_H
 #define BITCOIN_UTIL_OBFUSCATION_H
 
-#include <cstdint>
+#include <crypto/hex_base.h>
 #include <span.h>
 #include <tinyformat.h>
 #include <util/strencodings.h>
@@ -13,6 +13,7 @@
 #include <array>
 #include <bit>
 #include <climits>
+#include <cstdint>
 #include <ios>
 #include <memory>
 
diff --git a/src/util/overflow.h b/src/util/overflow.h
index 48df3549..274ba045 100644
--- a/src/util/overflow.h
+++ b/src/util/overflow.h
@@ -5,7 +5,8 @@
 #ifndef BITCOIN_UTIL_OVERFLOW_H
 #define BITCOIN_UTIL_OVERFLOW_H
 
-#include <cassert>
+#include <util/check.h>
+
 #include <climits>
 #include <concepts>
 #include <limits>
diff --git a/src/util/rbf.cpp b/src/util/rbf.cpp
index bc28c6bb..82ef020d 100644
--- a/src/util/rbf.cpp
+++ b/src/util/rbf.cpp
@@ -6,6 +6,8 @@
 
 #include <primitives/transaction.h>
 
+#include <vector>
+
 bool SignalsOptInRBF(const CTransaction &tx)
 {
     for (const CTxIn &txin : tx.vin) {
diff --git a/src/util/readwritefile.cpp b/src/util/readwritefile.cpp
index 82b596f9..6a9eeb28 100644
--- a/src/util/readwritefile.cpp
+++ b/src/util/readwritefile.cpp
@@ -9,7 +9,6 @@
 
 #include <algorithm>
 #include <cstdio>
-#include <limits>
 #include <string>
 #include <utility>
 
diff --git a/src/util/readwritefile.h b/src/util/readwritefile.h
index 2a9ccf5f..54a5a305 100644
--- a/src/util/readwritefile.h
+++ b/src/util/readwritefile.h
@@ -7,6 +7,7 @@
 
 #include <util/fs.h>
 
+#include <cstddef>
 #include <limits>
 #include <string>
 #include <utility>
diff --git a/src/util/signalinterrupt.h b/src/util/signalinterrupt.h
index 027dd153..5a23cd1e 100644
--- a/src/util/signalinterrupt.h
+++ b/src/util/signalinterrupt.h
@@ -13,7 +13,6 @@
 #endif
 
 #include <atomic>
-#include <cstdlib>
 
 namespace util {
 /**
diff --git a/src/util/sock.cpp b/src/util/sock.cpp
index a06ab7a7..8e0c0f47 100644
--- a/src/util/sock.cpp
+++ b/src/util/sock.cpp
@@ -4,18 +4,23 @@
 
 #include <util/sock.h>
 
-#include <common/system.h>
 #include <compat/compat.h>
 #include <span.h>
 #include <tinyformat.h>
+#include <util/check.h>
 #include <util/log.h>
 #include <util/syserror.h>
 #include <util/threadinterrupt.h>
 #include <util/time.h>
 
+#include <algorithm>
+#include <compare>
+#include <exception>
 #include <memory>
 #include <stdexcept>
 #include <string>
+#include <utility>
+#include <vector>
 
 #ifdef USE_POLL
 #include <poll.h>
diff --git a/src/util/sock.h b/src/util/sock.h
index 8c51b8ea..e20b31e1 100644
--- a/src/util/sock.h
+++ b/src/util/sock.h
@@ -6,15 +6,17 @@
 #define BITCOIN_UTIL_SOCK_H
 
 #include <compat/compat.h>
-#include <util/threadinterrupt.h>
 #include <util/time.h>
 
-#include <chrono>
+#include <cstdint>
+#include <limits>
 #include <memory>
 #include <span>
 #include <string>
 #include <unordered_map>
 
+class CThreadInterrupt;
+
 /**
  * Maximum time to wait for I/O readiness.
  * It will take up until this time to break off in case of an interruption.
diff --git a/src/util/strencodings.cpp b/src/util/strencodings.cpp
index ff593885..e64b677f 100644
--- a/src/util/strencodings.cpp
+++ b/src/util/strencodings.cpp
@@ -7,14 +7,13 @@
 
 #include <crypto/hex_base.h>
 #include <span.h>
+#include <util/check.h>
 #include <util/overflow.h>
 
-#include <array>
-#include <cassert>
-#include <cstring>
+#include <compare>
 #include <limits>
 #include <optional>
-#include <ostream>
+#include <sstream>
 #include <string>
 #include <vector>
 
diff --git a/src/util/strencodings.h b/src/util/strencodings.h
index faff83bb..e5279722 100644
--- a/src/util/strencodings.h
+++ b/src/util/strencodings.h
@@ -9,11 +9,9 @@
 #ifndef BITCOIN_UTIL_STRENCODINGS_H
 #define BITCOIN_UTIL_STRENCODINGS_H
 
-#include <crypto/hex_base.h>
 #include <span.h>
 #include <util/string.h>
 
-#include <algorithm>
 #include <array>
 #include <bit>
 #include <charconv>
@@ -21,6 +19,7 @@
 #include <cstdint>
 #include <limits>
 #include <optional>
+#include <span>
 #include <string>
 #include <string_view>
 #include <system_error>
diff --git a/src/util/string.cpp b/src/util/string.cpp
index c3b4b474..6e86095a 100644
--- a/src/util/string.cpp
+++ b/src/util/string.cpp
@@ -4,7 +4,10 @@
 
 #include <util/string.h>
 
+#include <iterator>
+#include <memory>
 #include <regex>
+#include <stdexcept>
 #include <string>
 
 namespace util {
diff --git a/src/util/string.h b/src/util/string.h
index 89e13099..20c78583 100644
--- a/src/util/string.h
+++ b/src/util/string.h
@@ -5,13 +5,14 @@
 #ifndef BITCOIN_UTIL_STRING_H
 #define BITCOIN_UTIL_STRING_H
 
-#include <span.h>
-
+#include <algorithm>
 #include <array>
+#include <cstddef>
 #include <cstdint>
-#include <cstring>
+#include <initializer_list>
 #include <locale>
 #include <optional>
+#include <span>
 #include <sstream>
 #include <string>
 #include <string_view>
diff --git a/src/util/subprocess.h b/src/util/subprocess.h
index 8b917130..3d01f4b7 100644
--- a/src/util/subprocess.h
+++ b/src/util/subprocess.h
@@ -36,10 +36,10 @@ Documentation for C++ subprocessing library.
 #ifndef BITCOIN_UTIL_SUBPROCESS_H
 #define BITCOIN_UTIL_SUBPROCESS_H
 
+#include <util/check.h>
 #include <util/syserror.h>
 
 #include <algorithm>
-#include <cassert>
 #include <csignal>
 #include <cstdio>
 #include <cstdlib>
diff --git a/src/util/syserror.cpp b/src/util/syserror.cpp
index e06ed0cd..e7637afe 100644
--- a/src/util/syserror.cpp
+++ b/src/util/syserror.cpp
@@ -4,9 +4,10 @@
 
 #include <bitcoin-build-config.h> // IWYU pragma: keep
 
-#include <tinyformat.h>
 #include <util/syserror.h>
 
+#include <tinyformat.h>
+
 #include <cstring>
 #include <string>
 
diff --git a/src/util/thread.cpp b/src/util/thread.cpp
index 0fde73c4..5b20e807 100644
--- a/src/util/thread.cpp
+++ b/src/util/thread.cpp
@@ -11,7 +11,6 @@
 #include <exception>
 #include <functional>
 #include <string>
-#include <utility>
 
 void util::TraceThread(std::string_view thread_name, std::function<void()> thread_func)
 {
diff --git a/src/util/thread.h b/src/util/thread.h
index cb1dd86a..d398b188 100644
--- a/src/util/thread.h
+++ b/src/util/thread.h
@@ -6,7 +6,7 @@
 #define BITCOIN_UTIL_THREAD_H
 
 #include <functional>
-#include <string>
+#include <string_view>
 
 namespace util {
 /**
diff --git a/src/util/threadinterrupt.h b/src/util/threadinterrupt.h
index 9cac330e..ba45f117 100644
--- a/src/util/threadinterrupt.h
+++ b/src/util/threadinterrupt.h
@@ -6,9 +6,9 @@
 #define BITCOIN_UTIL_THREADINTERRUPT_H
 
 #include <sync.h>
+#include <util/time.h>
 
 #include <atomic>
-#include <chrono>
 #include <condition_variable>
 
 /**
diff --git a/src/util/threadnames.cpp b/src/util/threadnames.cpp
index 310f60f6..0615b331 100644
--- a/src/util/threadnames.cpp
+++ b/src/util/threadnames.cpp
@@ -2,18 +2,17 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <util/threadnames.h>
+
+#include <algorithm>
 #include <cstring>
 #include <string>
-#include <thread>
-#include <utility>
 
 #if (defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__DragonFly__))
 #include <pthread.h>
 #include <pthread_np.h>
 #endif
 
-#include <util/threadnames.h>
-
 #if __has_include(<sys/prctl.h>)
 #include <sys/prctl.h>
 #endif
diff --git a/src/util/time.cpp b/src/util/time.cpp
index 9e0715e5..6a199ebc 100644
--- a/src/util/time.cpp
+++ b/src/util/time.cpp
@@ -5,7 +5,6 @@
 
 #include <util/time.h>
 
-#include <compat/compat.h>
 #include <tinyformat.h>
 #include <util/check.h>
 #include <util/strencodings.h>
@@ -13,11 +12,18 @@
 #include <array>
 #include <atomic>
 #include <chrono>
+#include <compare>
 #include <optional>
 #include <string>
 #include <string_view>
 #include <thread>
 
+#ifdef WIN32
+#include <winsock2.h>
+#else
+#include <sys/time.h>
+#endif
+
 static constexpr std::array<std::string_view, 7> weekdays{"Thu", "Fri", "Sat", "Sun", "Mon", "Tue", "Wed"}; // 1970-01-01 was a Thursday.
 static constexpr std::array<std::string_view, 12> months{"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
 
diff --git a/src/util/time.h b/src/util/time.h
index 30d363bb..46307989 100644
--- a/src/util/time.h
+++ b/src/util/time.h
@@ -9,10 +9,17 @@
 // The `util/time.h` header is designed to be a drop-in replacement for `chrono`.
 #include <chrono> // IWYU pragma: export
 #include <cstdint>
+#include <ctime>
 #include <optional>
 #include <string>
 #include <string_view>
 
+#ifdef WIN32
+#include <winsock2.h>
+#else
+#include <sys/time.h>
+#endif
+
 using namespace std::chrono_literals;
 
 /// Version of the system clock that is mockable in the context of tests (via
diff --git a/src/util/tokenpipe.cpp b/src/util/tokenpipe.cpp
index c982fa6f..6f701e45 100644
--- a/src/util/tokenpipe.cpp
+++ b/src/util/tokenpipe.cpp
@@ -1,15 +1,18 @@
 // Copyright (c) 2021-present The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
-#include <util/tokenpipe.h>
 
 #include <bitcoin-build-config.h> // IWYU pragma: keep
 
+#include <util/tokenpipe.h>
+
 #ifndef WIN32
 
 #include <cerrno>
-#include <fcntl.h>
 #include <optional>
+
+#include <fcntl.h>
+#include <sys/types.h>
 #include <unistd.h>
 
 TokenPipeEnd TokenPipe::TakeReadEnd()
diff --git a/src/util/translation.h b/src/util/translation.h
index cc29eef6..26fb4b8c 100644
--- a/src/util/translation.h
+++ b/src/util/translation.h
@@ -6,9 +6,9 @@
 #define BITCOIN_UTIL_TRANSLATION_H
 
 #include <tinyformat.h>
+#include <util/check.h>
 #include <util/string.h>
 
-#include <cassert>
 #include <functional>
 #include <string>