Replace Catch2's runner with the Catch3 runner

Catch3 keeps Catch2's API for writing tests (test cases, sections,
assertions, matchers, generators, listeners, benchmarks) and replaces its
session, command line and reporters with a runner of its own.

The runner starts the test binary again as worker processes that take the
next test when they are free. A crash, an exit or a hang ends one test, not
the run. On top of that it adds:

- retries that tell deterministic, flaky and order-dependent failures
  apart, and a bisection that names the test leaving state behind;
- a history of verdicts and durations, kept under a file lock, that drives
  automatic quarantine, adaptive time limits, predictive ordering,
  incremental runs, failure replay and analytics;
- selection by change, past failure or prediction, dependency closure,
  and sharding by a stable hash or by recorded durations;
- tags for serial and isolated tests, shared resources, dependencies,
  time limits and retries;
- a failure category, a signature, an analysis and a replay command for
  every failure;
- console, JUnit XML (with flakyFailure and rerunFailure), JSON and Chrome
  trace reports, and a versioned discovery listing (--list=json);
- a temporary directory per test (TMPDIR, TMP, TEMP and
  TestTemporaryDirectory());
- Bazel's test environment: XML output file, test filter, sharding, seed,
  premature exit file and undeclared outputs.

The command line is parsed by a hand-written, typed parser. Catch::Session
remains as a thin facade over the runner for custom main functions.

The result model in Progmasoft/Catch3/Results.hpp was rewritten around
tests and attempts, and the JUnit writer now writes it. The property
engine's example database is updated under a file lock with an atomic
rename, so parallel workers can write it at the same time.

Removed: Clara, the command-line and reporter-spec parsers, every reporter
and CATCH_REGISTER_REPORTER, listing, text flow, console colour and width,
the JSON and XML writers, sharding in the test registry, approval tests and
their baselines, Conan packaging, and the unused third_party/clara.hpp.
Listeners keep working; reporters' list and skip events are gone.

The Catch2 library is now compiled as C++20; code that includes only
Catch2's headers still needs C++14. Duplicate test cases are still refused
at start-up. Version 0.3.0.

ExtraTests now turn exceptions off for clang-cl with MSVC-style options,
which -fno-exceptions did not do.

1 files changed, 172 insertions, 0 deletions

diff --git a/src/Progmasoft/Runner/Git.cpp b/src/Progmasoft/Runner/Git.cpp
new file mode 100644
index 00000000..76548cbc
--- /dev/null
+++ b/src/Progmasoft/Runner/Git.cpp
@@ -0,0 +1,172 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+#include "Git.hpp"
+
+#include "Process.hpp"
+
+#include <algorithm>
+#include <cctype>
+#include <system_error>
+
+namespace Progmasoft::Catch3::Runner
+{
+    namespace
+    {
+        Expected<std::string>
+        Git(const std::filesystem::path &directory,
+            std::vector<std::string> arguments)
+        {
+            ChildOptions options;
+            options.arguments.emplace_back("git");
+            options.arguments.insert(
+                options.arguments.end(), arguments.begin(), arguments.end());
+            options.workingDirectory = directory;
+            options.searchPath = true;
+            auto run = RunAndCapture(options);
+            if (!run)
+            {
+                return run.GetError();
+            }
+            if (!run->status.Succeeded())
+            {
+                std::string message = run->errors;
+                while (!message.empty() &&
+                       (message.back() == '\n' || message.back() == '\r'))
+                {
+                    message.pop_back();
+                }
+                return Error{"git " + arguments.front() + " failed: " +
+                             message};
+            }
+            return run->output;
+        }
+
+        std::vector<std::string>
+        Lines(const std::string &text)
+        {
+            std::vector<std::string> lines;
+            std::size_t start = 0;
+            while (start < text.size())
+            {
+                auto end = text.find('\n', start);
+                if (end == std::string::npos)
+                {
+                    end = text.size();
+                }
+                std::string line = text.substr(start, end - start);
+                if (!line.empty() && line.back() == '\r')
+                {
+                    line.pop_back();
+                }
+                if (!line.empty())
+                {
+                    lines.push_back(std::move(line));
+                }
+                start = end + 1;
+            }
+            return lines;
+        }
+
+        std::string
+        Normalised(const std::filesystem::path &path)
+        {
+            std::string text = path.lexically_normal().generic_string();
+#if defined(_WIN32)
+            // Windows paths compare without case.
+            std::transform(text.begin(), text.end(), text.begin(), [](char c) {
+                return static_cast<char>(
+                    std::tolower(static_cast<unsigned char>(c)));
+            });
+#endif
+            return text;
+        }
+    } // namespace
+
+    Expected<Changes>
+    ReadChanges(const std::filesystem::path &directory,
+                const std::string &revision)
+    {
+        auto root = Git(directory, {"rev-parse", "--show-toplevel"});
+        if (!root)
+        {
+            return root.GetError();
+        }
+        Changes changes;
+        const auto rootLines = Lines(*root);
+        if (rootLines.empty())
+        {
+            return Error{"git did not name the top of the checkout"};
+        }
+        changes.root = std::filesystem::path{rootLines.front()};
+        changes.commit = CurrentCommit(directory);
+        const std::string base = revision.empty() ? "HEAD" : revision;
+        auto changed =
+            Git(changes.root, {"diff", "--name-only", "--no-renames", base});
+        if (!changed)
+        {
+            return changed.GetError();
+        }
+        auto untracked = Git(changes.root,
+                             {"ls-files", "--others", "--exclude-standard"});
+        for (const auto &line : Lines(*changed))
+        {
+            changes.files.push_back(changes.root / line);
+        }
+        if (untracked)
+        {
+            for (const auto &line : Lines(*untracked))
+            {
+                changes.files.push_back(changes.root / line);
+            }
+        }
+        return changes;
+    }
+
+    std::string
+    CurrentCommit(const std::filesystem::path &directory)
+    {
+        auto commit = Git(directory, {"rev-parse", "HEAD"});
+        if (!commit)
+        {
+            return {};
+        }
+        const auto lines = Lines(*commit);
+        return lines.empty() ? std::string{} : lines.front();
+    }
+
+    bool
+    SameSourceFile(const std::filesystem::path &left,
+                   const std::filesystem::path &right)
+    {
+        const std::string first = Normalised(left);
+        const std::string second = Normalised(right);
+        if (first == second)
+        {
+            return true;
+        }
+        const auto endsWith = [](const std::string &text,
+                                 const std::string &suffix) {
+            if (suffix.empty() || suffix.size() >= text.size())
+            {
+                return false;
+            }
+            return text.compare(text.size() - suffix.size(),
+                                suffix.size(),
+                                suffix) == 0 &&
+                   text[text.size() - suffix.size() - 1] == '/';
+        };
+        // __FILE__ is often relative to the build directory.
+        std::string relativeFirst = first;
+        std::string relativeSecond = second;
+        while (relativeFirst.rfind("../", 0) == 0)
+        {
+            relativeFirst.erase(0, 3);
+        }
+        while (relativeSecond.rfind("../", 0) == 0)
+        {
+            relativeSecond.erase(0, 3);
+        }
+        return (!left.is_absolute() && endsWith(second, relativeFirst)) ||
+               (!right.is_absolute() && endsWith(first, relativeSecond));
+    }
+} // namespace Progmasoft::Catch3::Runner