Add Progmasoft Catch3 property testing and build support0.1.0

Introduce deterministic property execution, built-in generators, shrinking, replayable seeds, and a separate Progmasoft-owned header API while preserving Catch2 compatibility targets and the C++14 engine baseline.

Add Bazel, Meson, Xmake, and Premake integration and tests alongside the existing CMake build. Replace Linux-only workflow coverage with Windows and macOS jobs and document the Catch2/Catch3 distinction.

11 files changed, 636 insertions, 0 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 886605f1..cb8c339d 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -360,6 +360,19 @@ if(CATCH_ENABLE_REPRODUCIBLE_BUILD)
 endif()
 add_library(Catch2::Catch2 ALIAS Catch2)
 
+# Progmasoft's C++20 additions are a separate target so the Catch2
+# compatibility engine can keep its existing, broader C++14 baseline.
+add_library(ProgmasoftCatch3 INTERFACE)
+add_library(Progmasoft::Catch3 ALIAS ProgmasoftCatch3)
+set_target_properties(ProgmasoftCatch3 PROPERTIES EXPORT_NAME Catch3)
+target_link_libraries(ProgmasoftCatch3 INTERFACE Catch2::Catch2)
+target_include_directories(ProgmasoftCatch3
+  INTERFACE
+    $<BUILD_INTERFACE:${CATCH_DIR}/src>
+    $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+)
+target_compile_features(ProgmasoftCatch3 INTERFACE cxx_std_20)
+
 if(ANDROID)
   target_link_libraries(Catch2 PRIVATE log)
 endif()
@@ -436,6 +449,36 @@ if(NOT_SUBPROJECT)
     FILES_MATCHING
       PATTERN "*.hpp"
   )
+
+  # Keep the independently licensed Progmasoft headers beside Catch2's public
+  # headers while preserving a separate CMake target and package namespace.
+  install(
+    DIRECTORY "${CATCH_DIR}/src/Progmasoft"
+    DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
+    FILES_MATCHING PATTERN "*.hpp"
+  )
+  install(TARGETS ProgmasoftCatch3 EXPORT ProgmasoftCatch3Targets)
+  install(
+    EXPORT ProgmasoftCatch3Targets
+    NAMESPACE Progmasoft::
+    DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/ProgmasoftCatch3"
+  )
+  configure_package_config_file(
+    "${CATCH_DIR}/src/Progmasoft/ProgmasoftCatch3Config.cmake.in"
+    "${PROJECT_BINARY_DIR}/ProgmasoftCatch3Config.cmake"
+    INSTALL_DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/ProgmasoftCatch3"
+  )
+  write_basic_package_version_file(
+    "${PROJECT_BINARY_DIR}/ProgmasoftCatch3ConfigVersion.cmake"
+    VERSION "${PROJECT_VERSION}"
+    COMPATIBILITY SameMajorVersion
+  )
+  install(
+    FILES
+      "${PROJECT_BINARY_DIR}/ProgmasoftCatch3Config.cmake"
+      "${PROJECT_BINARY_DIR}/ProgmasoftCatch3ConfigVersion.cmake"
+    DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/ProgmasoftCatch3"
+  )
 endif()
 
 # Some tests require a full recompilation of Catch2 lib with different
diff --git a/src/Progmasoft/BUILD.bazel b/src/Progmasoft/BUILD.bazel
new file mode 100644
index 00000000..9927aafa
--- /dev/null
+++ b/src/Progmasoft/BUILD.bazel
@@ -0,0 +1,20 @@
+# Copyright (c) 2026 Progmasoft.
+# SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+load("@rules_cc//cc:defs.bzl", "cc_library")
+
+package(default_visibility = ["//visibility:public"])
+
+cc_library(
+    name = "catch3",
+    hdrs = [
+        "Catch3.hpp",
+        "Catch3/Assertions.hpp",
+        "Catch3/Generator.hpp",
+        "Catch3/Generators/Boolean.hpp",
+        "Catch3/Generators/Integer.hpp",
+        "Catch3/Property.hpp",
+        "Catch3/Random.hpp",
+    ],
+    strip_include_prefix = "/src",
+    deps = ["//:catch2"],
+)
diff --git a/src/Progmasoft/Catch3.hpp b/src/Progmasoft/Catch3.hpp
new file mode 100644
index 00000000..1ae73e53
--- /dev/null
+++ b/src/Progmasoft/Catch3.hpp
@@ -0,0 +1,13 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+#pragma once
+
+// Convenience include: prefer narrow headers when compile time matters.
+#include <catch2/catch_all.hpp>
+
+#include <Progmasoft/Catch3/Assertions.hpp>
+#include <Progmasoft/Catch3/Generator.hpp>
+#include <Progmasoft/Catch3/Generators/Boolean.hpp>
+#include <Progmasoft/Catch3/Generators/Integer.hpp>
+#include <Progmasoft/Catch3/Property.hpp>
+#include <Progmasoft/Catch3/Random.hpp>
diff --git a/src/Progmasoft/Catch3/Assertions.hpp b/src/Progmasoft/Catch3/Assertions.hpp
new file mode 100644
index 00000000..19ac13ef
--- /dev/null
+++ b/src/Progmasoft/Catch3/Assertions.hpp
@@ -0,0 +1,17 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+#pragma once
+
+#include <catch2/catch_message.hpp>
+#include <catch2/catch_test_macros.hpp>
+
+#include <Progmasoft/Catch3/Property.hpp>
+
+/// Runs a property and reports its replay seed and minimized counterexample.
+#define CATCH3_CHECK_PROPERTY( ... )                            \
+    do {                                                        \
+        const auto catch3PropertyResult =                       \
+            ::Progmasoft::Catch3::CheckProperty( __VA_ARGS__ ); \
+        INFO( catch3PropertyResult.Describe() );                \
+        CHECK( catch3PropertyResult.Succeeded() );              \
+    } while ( false )
diff --git a/src/Progmasoft/Catch3/Generator.hpp b/src/Progmasoft/Catch3/Generator.hpp
new file mode 100644
index 00000000..0e48aaa3
--- /dev/null
+++ b/src/Progmasoft/Catch3/Generator.hpp
@@ -0,0 +1,61 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+#pragma once
+
+#include <Progmasoft/Catch3/Random.hpp>
+
+#include <functional>
+#include <stdexcept>
+#include <utility>
+#include <vector>
+
+namespace Progmasoft::Catch3 {
+
+    /// A value source paired with an ordered sequence of simpler candidates.
+    ///
+    /// The property runner owns the shrinking policy; generators only describe
+    /// which candidates are valid and which order is most useful for
+    /// minimization.
+    template <typename ValueType>
+    class Generator final {
+    public:
+        using GenerationFunction = std::function<ValueType( Random& )>;
+        using ShrinkingFunction =
+            std::function<std::vector<ValueType>( const ValueType& )>;
+
+        Generator( GenerationFunction generate, ShrinkingFunction shrink ):
+            generate_( std::move( generate ) ), shrink_( std::move( shrink ) ) {
+            if ( !generate_ || !shrink_ ) {
+                throw std::invalid_argument(
+                    "a generator requires both callbacks" );
+            }
+        }
+
+        [[nodiscard]] ValueType Generate( Random& random ) const {
+            return generate_( random );
+        }
+
+        [[nodiscard]] std::vector<ValueType>
+        Shrink( const ValueType& value ) const {
+            return shrink_( value );
+        }
+
+    private:
+        GenerationFunction generate_;
+        ShrinkingFunction shrink_;
+    };
+
+    /// Adapts user callables into a reusable generator.
+    template <typename ValueType,
+              typename GenerateFunction,
+              typename ShrinkFunction>
+    [[nodiscard]] Generator<ValueType>
+    MakeGenerator( GenerateFunction&& generate, ShrinkFunction&& shrink ) {
+        return Generator<ValueType>(
+            typename Generator<ValueType>::GenerationFunction(
+                std::forward<GenerateFunction>( generate ) ),
+            typename Generator<ValueType>::ShrinkingFunction(
+                std::forward<ShrinkFunction>( shrink ) ) );
+    }
+
+} // namespace Progmasoft::Catch3
diff --git a/src/Progmasoft/Catch3/Generators/Boolean.hpp b/src/Progmasoft/Catch3/Generators/Boolean.hpp
new file mode 100644
index 00000000..3f881927
--- /dev/null
+++ b/src/Progmasoft/Catch3/Generators/Boolean.hpp
@@ -0,0 +1,18 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+#pragma once
+
+#include <Progmasoft/Catch3/Generator.hpp>
+
+namespace Progmasoft::Catch3 {
+
+    /// Generates booleans and shrinks true to the simplest value, false.
+    [[nodiscard]] inline Generator<bool> Boolean() {
+        return MakeGenerator<bool>(
+            []( Random& random ) { return ( random.Next() & 1U ) != 0; },
+            []( const bool& value ) {
+                return value ? std::vector<bool>{ false } : std::vector<bool>{};
+            } );
+    }
+
+} // namespace Progmasoft::Catch3
diff --git a/src/Progmasoft/Catch3/Generators/Integer.hpp b/src/Progmasoft/Catch3/Generators/Integer.hpp
new file mode 100644
index 00000000..2a50525e
--- /dev/null
+++ b/src/Progmasoft/Catch3/Generators/Integer.hpp
@@ -0,0 +1,82 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+#pragma once
+
+#include <Progmasoft/Catch3/Generator.hpp>
+
+#include <algorithm>
+#include <concepts>
+#include <limits>
+#include <type_traits>
+
+namespace Progmasoft::Catch3 {
+    namespace Detail {
+
+        template <std::integral IntegerType>
+        requires( !std::same_as<IntegerType, bool> )
+            [[nodiscard]] std::vector<IntegerType> ShrinkInteger(
+                IntegerType value, IntegerType minimum, IntegerType maximum ) {
+            std::vector<IntegerType> candidates;
+            const auto addCandidate = [&]( IntegerType candidate ) {
+                if ( candidate < minimum || candidate > maximum ||
+                     candidate == value ||
+                     std::ranges::find( candidates, candidate ) !=
+                         candidates.end() ) {
+                    return;
+                }
+                candidates.push_back( candidate );
+            };
+
+            if ( value == 0 ) { return candidates; }
+
+            // First try the conventional simplest value, then halve toward it.
+            // The adjacent value at the end lets the runner find boundary
+            // counterexamples (for example, the first failing integer in a
+            // threshold property).
+            if ( minimum <= 0 && maximum >= 0 ) { addCandidate( 0 ); }
+
+            IntegerType smaller = value;
+            while ( smaller != 0 ) {
+                smaller = static_cast<IntegerType>( smaller / 2 );
+                if ( smaller == 0 ) { break; }
+                addCandidate( smaller );
+            }
+
+            if ( value > 0 ) {
+                if ( value > minimum ) {
+                    addCandidate( static_cast<IntegerType>( value - 1 ) );
+                }
+                if ( minimum > 0 ) { addCandidate( minimum ); }
+            } else {
+                if ( value < maximum ) {
+                    addCandidate( static_cast<IntegerType>( value + 1 ) );
+                }
+                if ( maximum < 0 ) { addCandidate( maximum ); }
+            }
+            return candidates;
+        }
+
+    } // namespace Detail
+
+    /// Generates integers over the inclusive range and shrinks toward simple
+    /// values.
+    template <std::integral IntegerType>
+    requires( !std::same_as<IntegerType, bool> )
+        [[nodiscard]] Generator<IntegerType> Integer(
+            IntegerType minimum = std::numeric_limits<IntegerType>::lowest(),
+            IntegerType maximum = std::numeric_limits<IntegerType>::max() ) {
+        if ( minimum > maximum ) {
+            throw std::invalid_argument(
+                "Integer requires minimum <= maximum" );
+        }
+
+        return MakeGenerator<IntegerType>(
+            [minimum, maximum]( Random& random ) {
+                return random.Between( minimum, maximum );
+            },
+            [minimum, maximum]( const IntegerType& value ) {
+                return Detail::ShrinkInteger( value, minimum, maximum );
+            } );
+    }
+
+} // namespace Progmasoft::Catch3
diff --git a/src/Progmasoft/Catch3/Property.hpp b/src/Progmasoft/Catch3/Property.hpp
new file mode 100644
index 00000000..57e74408
--- /dev/null
+++ b/src/Progmasoft/Catch3/Property.hpp
@@ -0,0 +1,244 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+#pragma once
+
+#include <catch2/catch_tostring.hpp>
+
+#include <Progmasoft/Catch3/Generator.hpp>
+
+#include <concepts>
+#include <cstddef>
+#include <cstdint>
+#include <exception>
+#include <functional>
+#include <optional>
+#include <sstream>
+#include <string>
+#include <type_traits>
+#include <utility>
+
+namespace Progmasoft::Catch3 {
+
+    /// Controls a property run without changing the compatibility runner's CLI.
+    struct PropertyOptions final {
+        std::size_t Trials = 100;
+        std::uint64_t Seed = 0xC47C4A53ULL;
+        std::size_t MaxShrinkSteps = 1000;
+    };
+
+    enum class PropertyStatus : std::uint8_t {
+        kPassed,
+        kFailed,
+        kErrored,
+        kInvalidConfiguration,
+    };
+
+    struct PropertyFailure final {
+        std::uint64_t RootSeed = 0;
+        std::uint64_t TrialSeed = 0;
+        std::size_t Trial = 0;
+        std::size_t ShrinkSteps = 0;
+        std::string Counterexample;
+        std::string Reason;
+    };
+
+    /// Stable, machine-readable outcome with a deterministic human-readable
+    /// report.
+    struct PropertyResult final {
+        PropertyStatus Status = PropertyStatus::kPassed;
+        std::size_t TrialsRun = 0;
+        std::optional<PropertyFailure> Failure;
+        std::string Error;
+
+        [[nodiscard]] bool Succeeded() const noexcept {
+            return Status == PropertyStatus::kPassed;
+        }
+
+        [[nodiscard]] std::string Describe() const {
+            std::ostringstream output;
+            switch ( Status ) {
+            case PropertyStatus::kPassed:
+                output << "property passed: " << TrialsRun << " trials";
+                return output.str();
+            case PropertyStatus::kInvalidConfiguration:
+                output << "invalid property configuration: " << Error;
+                return output.str();
+            case PropertyStatus::kErrored:
+                output << "property execution errored after " << TrialsRun
+                       << " trials: " << Error;
+                break;
+            case PropertyStatus::kFailed:
+                output << "property failed after " << TrialsRun << " trials";
+                break;
+            }
+
+            if ( Failure.has_value() ) {
+                output << "; failing trial " << Failure->Trial << ", root seed "
+                       << Failure->RootSeed << ", replay seed "
+                       << Failure->TrialSeed << ", shrink checks "
+                       << Failure->ShrinkSteps
+                       << "\ncounterexample: " << Failure->Counterexample
+                       << "\nreason: " << Failure->Reason;
+            }
+            return output.str();
+        }
+    };
+
+    namespace Detail {
+
+        template <typename ValueType>
+        [[nodiscard]] std::string
+        StringifyPropertyValue( const ValueType& value ) {
+            return Catch::StringMaker<std::remove_cvref_t<ValueType>>::convert(
+                value );
+        }
+
+        template <typename Predicate, typename ValueType>
+        [[nodiscard]] std::optional<std::string>
+        EvaluateProperty( Predicate& predicate, const ValueType& value ) {
+            try {
+                if ( static_cast<bool>( std::invoke( predicate, value ) ) ) {
+                    return std::nullopt;
+                }
+                return "predicate returned false";
+            } catch ( const std::exception& exception ) {
+                return std::string( "predicate threw std::exception: " ) +
+                       exception.what();
+            } catch ( ... ) {
+                return "predicate threw a non-standard exception";
+            }
+        }
+
+        template <typename ValueType>
+        [[nodiscard]] std::string
+        DescribeValue( const ValueType& value ) noexcept {
+            try {
+                return StringifyPropertyValue( value );
+            } catch ( const std::exception& exception ) {
+                return std::string( "<stringification failed: " ) +
+                       exception.what() + ">";
+            } catch ( ... ) {
+                return "<stringification failed with a non-standard exception>";
+            }
+        }
+
+    } // namespace Detail
+
+    /// Runs independently seeded trials and greedily accepts failing shrink
+    /// candidates.
+    template <typename ValueType, typename Predicate>
+    requires std::invocable<Predicate&, const ValueType&>&&
+        std::convertible_to<std::invoke_result_t<Predicate&, const ValueType&>,
+                            bool> [[nodiscard]] PropertyResult
+        CheckProperty( const Generator<ValueType>& generator,
+                       Predicate predicate,
+                       PropertyOptions options = {} ) {
+        if ( options.Trials == 0 ) {
+            return { PropertyStatus::kInvalidConfiguration,
+                     0,
+                     std::nullopt,
+                     "Trials must be greater than zero" };
+        }
+
+        PropertyResult result;
+        for ( std::size_t trial = 0; trial < options.Trials; ++trial ) {
+            result.TrialsRun = trial + 1;
+            const std::uint64_t trialSeed =
+                Random::DeriveSeed( options.Seed, trial );
+            Random random( trialSeed );
+            std::optional<ValueType> sample;
+
+            try {
+                sample.emplace( generator.Generate( random ) );
+            } catch ( const std::exception& exception ) {
+                result.Status = PropertyStatus::kErrored;
+                result.Error =
+                    std::string( "generator threw std::exception: " ) +
+                    exception.what();
+                result.Failure = PropertyFailure{ options.Seed,
+                                                  trialSeed,
+                                                  trial + 1,
+                                                  0,
+                                                  "<not generated>",
+                                                  result.Error };
+                return result;
+            } catch ( ... ) {
+                result.Status = PropertyStatus::kErrored;
+                result.Error = "generator threw a non-standard exception";
+                result.Failure = PropertyFailure{ options.Seed,
+                                                  trialSeed,
+                                                  trial + 1,
+                                                  0,
+                                                  "<not generated>",
+                                                  result.Error };
+                return result;
+            }
+
+            auto reason = Detail::EvaluateProperty( predicate, *sample );
+            if ( !reason.has_value() ) { continue; }
+
+            std::size_t shrinkChecks = 0;
+            try {
+                bool improved = true;
+                while ( improved && shrinkChecks < options.MaxShrinkSteps ) {
+                    improved = false;
+                    const std::vector<ValueType> candidates =
+                        generator.Shrink( *sample );
+                    for ( std::size_t candidateIndex = 0;
+                          candidateIndex < candidates.size();
+                          ++candidateIndex ) {
+                        if ( shrinkChecks >= options.MaxShrinkSteps ) { break; }
+                        ++shrinkChecks;
+                        const ValueType candidate = static_cast<ValueType>(
+                            candidates[candidateIndex] );
+                        auto candidateReason =
+                            Detail::EvaluateProperty( predicate, candidate );
+                        if ( candidateReason.has_value() ) {
+                            sample.emplace( candidate );
+                            reason = std::move( candidateReason );
+                            improved = true;
+                            break;
+                        }
+                    }
+                }
+            } catch ( const std::exception& exception ) {
+                result.Status = PropertyStatus::kErrored;
+                result.Error =
+                    std::string( "shrinker threw std::exception: " ) +
+                    exception.what();
+                result.Failure =
+                    PropertyFailure{ options.Seed,
+                                     trialSeed,
+                                     trial + 1,
+                                     shrinkChecks,
+                                     Detail::DescribeValue( *sample ),
+                                     *reason };
+                return result;
+            } catch ( ... ) {
+                result.Status = PropertyStatus::kErrored;
+                result.Error = "shrinker threw a non-standard exception";
+                result.Failure =
+                    PropertyFailure{ options.Seed,
+                                     trialSeed,
+                                     trial + 1,
+                                     shrinkChecks,
+                                     Detail::DescribeValue( *sample ),
+                                     *reason };
+                return result;
+            }
+
+            result.Status = PropertyStatus::kFailed;
+            result.Failure = PropertyFailure{ options.Seed,
+                                              trialSeed,
+                                              trial + 1,
+                                              shrinkChecks,
+                                              Detail::DescribeValue( *sample ),
+                                              *reason };
+            return result;
+        }
+
+        result.Status = PropertyStatus::kPassed;
+        return result;
+    }
+
+} // namespace Progmasoft::Catch3
diff --git a/src/Progmasoft/Catch3/Random.hpp b/src/Progmasoft/Catch3/Random.hpp
new file mode 100644
index 00000000..0a95cb84
--- /dev/null
+++ b/src/Progmasoft/Catch3/Random.hpp
@@ -0,0 +1,113 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+#pragma once
+
+#include <bit>
+#include <concepts>
+#include <cstdint>
+#include <limits>
+#include <stdexcept>
+#include <type_traits>
+
+namespace Progmasoft::Catch3 {
+
+    /// Small, deterministic random source for repeatable property-test cases.
+    ///
+    /// The SplitMix64 sequence is specified here instead of delegating to a
+    /// standard-library engine, whose output sequence is not portable between
+    /// library implementations. A Random object is intentionally not
+    /// thread-safe; property trials receive independent instances derived from
+    /// the root seed.
+    class Random final {
+    public:
+        explicit constexpr Random( std::uint64_t seed ) noexcept:
+            state_( seed ) {}
+
+        /// Returns the next value in the stable SplitMix64 sequence.
+        [[nodiscard]] constexpr std::uint64_t Next() noexcept {
+            state_ += kGamma;
+            std::uint64_t value = state_;
+            value = ( value ^ ( value >> 30U ) ) * kMultiplierOne;
+            value = ( value ^ ( value >> 27U ) ) * kMultiplierTwo;
+            return value ^ ( value >> 31U );
+        }
+
+        /// Returns a value in [0, bound); bound == 0 requests the full uint64
+        /// range.
+        [[nodiscard]] constexpr std::uint64_t
+        Below( std::uint64_t bound ) noexcept {
+            if ( bound == 0 ) { return Next(); }
+
+            // Rejection sampling avoids the modulo bias of a single `% bound`.
+            const std::uint64_t threshold =
+                ( std::uint64_t{ 0 } - bound ) % bound;
+            while ( true ) {
+                const std::uint64_t value = Next();
+                if ( value >= threshold ) { return value % bound; }
+            }
+        }
+
+        /// Returns an inclusive integral value without overflowing at type
+        /// limits.
+        template <std::integral IntegerType>
+        requires( !std::same_as<IntegerType, bool> ) [[nodiscard]] IntegerType
+            Between( IntegerType minimum, IntegerType maximum ) {
+            if ( minimum > maximum ) {
+                throw std::invalid_argument(
+                    "Random::Between requires minimum <= maximum" );
+            }
+
+            using UnsignedType = std::make_unsigned_t<IntegerType>;
+            static_assert( std::numeric_limits<UnsignedType>::digits <= 64 );
+
+            constexpr unsigned kBitCount = static_cast<unsigned>(
+                std::numeric_limits<UnsignedType>::digits );
+            constexpr UnsignedType kSignBit = UnsignedType{ 1 }
+                                              << ( kBitCount - 1U );
+
+            const auto encode =
+                []( IntegerType value ) constexpr -> UnsignedType {
+                if constexpr ( std::is_signed_v<IntegerType> ) {
+                    return std::bit_cast<UnsignedType>( value ) ^ kSignBit;
+                } else {
+                    return value;
+                }
+            };
+            const auto decode =
+                []( UnsignedType value ) constexpr -> IntegerType {
+                if constexpr ( std::is_signed_v<IntegerType> ) {
+                    return std::bit_cast<IntegerType>( value ^ kSignBit );
+                } else {
+                    return value;
+                }
+            };
+
+            const UnsignedType lower = encode( minimum );
+            const UnsignedType upper = encode( maximum );
+            // Unsigned wrap to zero represents the complete value domain.
+            const UnsignedType width =
+                static_cast<UnsignedType>( upper - lower + UnsignedType{ 1 } );
+            const UnsignedType offset =
+                width == 0 ? static_cast<UnsignedType>( Next() )
+                           : static_cast<UnsignedType>(
+                                 Below( static_cast<std::uint64_t>( width ) ) );
+            return decode( static_cast<UnsignedType>( lower + offset ) );
+        }
+
+        /// Derives an independent, reproducible seed for one trial.
+        [[nodiscard]] static constexpr std::uint64_t
+        DeriveSeed( std::uint64_t rootSeed,
+                    std::uint64_t trialIndex ) noexcept {
+            Random trialRandom( rootSeed + kGamma * ( trialIndex + 1U ) );
+            return trialRandom.Next();
+        }
+
+    private:
+        static constexpr std::uint64_t kGamma = 0x9E3779B97F4A7C15ULL;
+        static constexpr std::uint64_t kMultiplierOne = 0xBF58476D1CE4E5B9ULL;
+        static constexpr std::uint64_t kMultiplierTwo = 0x94D049BB133111EBULL;
+
+        std::uint64_t state_;
+    };
+
+} // namespace Progmasoft::Catch3
diff --git a/src/Progmasoft/ProgmasoftCatch3Config.cmake.in b/src/Progmasoft/ProgmasoftCatch3Config.cmake.in
new file mode 100644
index 00000000..a4b3ff31
--- /dev/null
+++ b/src/Progmasoft/ProgmasoftCatch3Config.cmake.in
@@ -0,0 +1,7 @@
+# Copyright (c) 2026 Progmasoft.
+# SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+@PACKAGE_INIT@
+
+include(CMakeFindDependencyMacro)
+find_dependency(Catch2 @PROJECT_VERSION@ CONFIG REQUIRED)
+include("${CMAKE_CURRENT_LIST_DIR}/ProgmasoftCatch3Targets.cmake")
diff --git a/src/Progmasoft/meson.build b/src/Progmasoft/meson.build
new file mode 100644
index 00000000..109edaa4
--- /dev/null
+++ b/src/Progmasoft/meson.build
@@ -0,0 +1,18 @@
+# Copyright (c) 2026 Progmasoft.
+# SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+
+# Expose the header-only C++20 layer without raising Catch2's C++14 baseline.
+progmasoft_catch3_dep = declare_dependency(
+  dependencies: catch2_dep,
+  include_directories: include_directories('..'),
+)
+
+if get_option('install')
+  install_headers('Catch3.hpp', subdir: 'Progmasoft')
+  install_headers('Catch3/Assertions.hpp', subdir: 'Progmasoft/Catch3')
+  install_headers('Catch3/Generator.hpp', subdir: 'Progmasoft/Catch3')
+  install_headers('Catch3/Property.hpp', subdir: 'Progmasoft/Catch3')
+  install_headers('Catch3/Random.hpp', subdir: 'Progmasoft/Catch3')
+  install_headers('Catch3/Generators/Boolean.hpp', subdir: 'Progmasoft/Catch3/Generators')
+  install_headers('Catch3/Generators/Integer.hpp', subdir: 'Progmasoft/Catch3/Generators')
+endif