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.

36 files changed, 11569 insertions, 0 deletions

diff --git a/src/Progmasoft/Runner/.clang-format b/src/Progmasoft/Runner/.clang-format
new file mode 100644
index 00000000..1063b9ea
--- /dev/null
+++ b/src/Progmasoft/Runner/.clang-format
@@ -0,0 +1,112 @@
+---
+Language: Cpp
+BasedOnStyle: LLVM
+Standard: c++20
+
+UseTab: Never
+IndentWidth: 4
+ContinuationIndentWidth: 4
+ConstructorInitializerIndentWidth: 4
+AccessModifierOffset: -4
+IndentAccessModifiers: false
+ColumnLimit: 80
+
+BreakBeforeBraces: Custom
+BraceWrapping:
+  AfterCaseLabel: true
+  AfterClass: true
+  AfterControlStatement: Always
+  AfterEnum: true
+  AfterExternBlock: true
+  AfterFunction: true
+  AfterNamespace: true
+  AfterStruct: true
+  AfterUnion: true
+  BeforeCatch: true
+  BeforeElse: true
+  BeforeLambdaBody: false
+  BeforeWhile: false
+  IndentBraces: false
+  SplitEmptyFunction: false
+  SplitEmptyRecord: false
+  SplitEmptyNamespace: false
+
+AllowShortBlocksOnASingleLine: Never
+AllowShortCaseLabelsOnASingleLine: false
+AllowShortEnumsOnASingleLine: false
+AllowShortFunctionsOnASingleLine: None
+AllowShortIfStatementsOnASingleLine: Never
+AllowShortLambdasOnASingleLine: None
+AllowShortLoopsOnASingleLine: false
+AllowShortNamespacesOnASingleLine: false
+AllowShortRecordOnASingleLine: Never
+
+BreakAfterReturnType: All
+
+PackArguments:
+  BinPack: OnePerLine
+PackParameters:
+  BinPack: OnePerLine
+AllowAllArgumentsOnNextLine: false
+AllowAllParametersOfDeclarationOnNextLine: false
+
+BreakBeforeBinaryOperators: All
+BreakBeforeTernaryOperators: true
+AlignOperands: Align
+
+BreakConstructorInitializers: BeforeComma
+PackConstructorInitializers: Never
+BreakInheritanceList: BeforeComma
+
+PointerAlignment: Right
+DerivePointerAlignment: false
+QualifierAlignment: Leave
+
+SpaceBeforeParens: ControlStatements
+SpaceBeforeAssignmentOperators: true
+SpaceBeforeCaseColon: false
+SpaceBeforeCtorInitializerColon: false
+SpaceBeforeInheritanceColon: false
+SpaceBeforeCpp11BracedList: false
+SpacesInAngles: Never
+SpacesInSquareBrackets: false
+SpacesInParens: Never
+SpaceInEmptyBraces: Never
+
+Cpp11BracedListStyle: Block
+
+SpaceAfterTemplateKeyword: false
+BreakTemplateDeclarations: Yes
+
+IndentCaseLabels: true
+IndentCaseBlocks: false
+
+NamespaceIndentation: All
+FixNamespaceComments: true
+ShortNamespaceLines: 0
+CompactNamespaces: false
+
+IndentPPDirectives: AfterHash
+PPIndentWidth: 4
+
+IncludeBlocks: Regroup
+SortIncludes: CaseSensitive
+IncludeIsMainRegex: '$^'
+IncludeCategories:
+  - Regex: '^<.*>$'
+    Priority: 1
+    SortPriority: 1
+  - Regex: '^".*"$'
+    Priority: 2
+    SortPriority: 2
+
+MaxEmptyLinesToKeep: 1
+KeepEmptyLines:
+  AtStartOfBlock: false
+
+ReflowComments: true
+SortUsingDeclarations: Lexicographic
+
+LineEnding: DeriveLF
+InsertNewlineAtEOF: true
+...
diff --git a/src/Progmasoft/Runner/Analysis.cpp b/src/Progmasoft/Runner/Analysis.cpp
new file mode 100644
index 00000000..e1435cef
--- /dev/null
+++ b/src/Progmasoft/Runner/Analysis.cpp
@@ -0,0 +1,365 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+#include "Analysis.hpp"
+
+#include "Hash.hpp"
+
+#include <algorithm>
+#include <cctype>
+#include <map>
+
+namespace Progmasoft::Catch3::Runner
+{
+    namespace
+    {
+        /// Replaces what differs between two runs of the same failure:
+        /// numbers, hexadecimal addresses and the temporary directory.
+        std::string
+        Normalise(std::string_view text)
+        {
+            std::string result;
+            bool inNumber = false;
+            for (std::size_t index = 0; index < text.size(); ++index)
+            {
+                const char character = text[index];
+                const bool digit =
+                    std::isdigit(static_cast<unsigned char>(character)) != 0;
+                const bool hexLetter =
+                    inNumber &&
+                    std::isxdigit(static_cast<unsigned char>(character)) != 0;
+                if (digit || hexLetter ||
+                    (inNumber && (character == 'x' || character == '.')))
+                {
+                    if (!inNumber)
+                    {
+                        result.push_back('#');
+                    }
+                    inNumber = true;
+                    continue;
+                }
+                inNumber = false;
+                result.push_back(character);
+            }
+            return result;
+        }
+
+        const Attempt *
+        FirstFailure(const TestResult &test)
+        {
+            for (const auto &attempt : test.attempts)
+            {
+                if (IsFailure(attempt.outcome))
+                {
+                    return &attempt;
+                }
+            }
+            return nullptr;
+        }
+
+        std::string
+        Seconds(std::int64_t microseconds)
+        {
+            const auto tenths = (microseconds + 50000) / 100000;
+            return std::to_string(tenths / 10) + "." +
+                   std::to_string(tenths % 10) + " s";
+        }
+
+        std::string
+        OpenSections(const Attempt &attempt)
+        {
+            std::vector<std::string> open;
+            for (const auto &section : attempt.sections)
+            {
+                if (section.durationMicroseconds < 0)
+                {
+                    open.resize(section.depth);
+                    open.push_back(section.name);
+                }
+            }
+            std::string text;
+            for (const auto &name : open)
+            {
+                text += text.empty() ? "" : " / ";
+                text += name;
+            }
+            return text;
+        }
+
+        std::string
+        QuoteArgument(const std::string &argument)
+        {
+            if (argument.find_first_of(" \t\"'\\$`&|;<>()[]*?~!#") ==
+                    std::string::npos &&
+                !argument.empty())
+            {
+                return argument;
+            }
+            std::string quoted = "\"";
+            for (const char character : argument)
+            {
+                if (character == '"' || character == '\\' || character == '$' ||
+                    character == '`')
+                {
+                    quoted.push_back('\\');
+                }
+                quoted.push_back(character);
+            }
+            quoted.push_back('"');
+            return quoted;
+        }
+    } // namespace
+
+    std::string
+    QuoteTestSpec(const std::string &name)
+    {
+        // Catch2's spec syntax gives these characters a meaning; a backslash
+        // makes them literal.
+        std::string spec;
+        for (const char character : name)
+        {
+            if (character == ',' || character == '[' || character == ']' ||
+                character == '*' || character == '\\' || character == '~' ||
+                character == '"')
+            {
+                spec.push_back('\\');
+            }
+            spec.push_back(character);
+        }
+        return spec;
+    }
+
+    std::string
+    FailureSignature(const Attempt &attempt)
+    {
+        std::string text = CategoryName(attempt.category);
+        text += '|';
+        bool described = false;
+        for (const auto &assertion : attempt.assertions)
+        {
+            if (assertion.passed || assertion.allowed)
+            {
+                continue;
+            }
+            text += assertion.file + ":" + std::to_string(assertion.line) +
+                    "|" + Normalise(assertion.message) + "|" +
+                    assertion.expression;
+            described = true;
+            break;
+        }
+        if (!described)
+        {
+            text += Normalise(attempt.fatalMessage) + "|" +
+                    attempt.lastLocation + "|" + OpenSections(attempt);
+        }
+        return "sig-" + ToHex(Fnv1a64(text)).substr(0, 12);
+    }
+
+    void
+    Analyze(RunResult &run, const AnalysisInputs &inputs)
+    {
+        std::map<std::string, std::vector<std::size_t>> bySignature;
+        for (std::size_t index = 0; index < run.tests.size(); ++index)
+        {
+            TestResult &test = run.tests[index];
+            const Attempt *failure = FirstFailure(test);
+            if (failure == nullptr)
+            {
+                continue;
+            }
+            test.signature = FailureSignature(*failure);
+            bySignature[test.signature].push_back(index);
+        }
+
+        for (std::size_t index = 0; index < run.tests.size(); ++index)
+        {
+            TestResult &test = run.tests[index];
+            const Attempt *failure = FirstFailure(test);
+            if (failure == nullptr)
+            {
+                continue;
+            }
+            std::vector<std::string> findings;
+
+            // How it relates to earlier runs.
+            const TestHistory *past =
+                inputs.history == nullptr ? nullptr
+                                          : inputs.history->Find(test.id);
+            const TestRecord *last = past == nullptr ? nullptr : past->Last();
+            if (last == nullptr)
+            {
+                test.history = FailureHistory::kUnknown;
+            }
+            else if (test.flaky || past->FlakyEvents(20) > 0)
+            {
+                test.history = FailureHistory::kIntermittent;
+                const auto events = past->FlakyEvents(20) + (test.flaky ? 1 : 0);
+                findings.push_back("intermittent: " + std::to_string(events) +
+                                   " flaky result(s) in the last 20 runs");
+            }
+            else if (IsFailure(last->outcome))
+            {
+                test.history = FailureHistory::kPersistent;
+                std::size_t streak = 0;
+                for (auto record = past->records.rbegin();
+                     record != past->records.rend() &&
+                     IsFailure(record->outcome);
+                     ++record)
+                {
+                    ++streak;
+                }
+                std::string finding = "persistent: failed in the last " +
+                                      std::to_string(streak) + " run(s)";
+                if (!last->signature.empty() && last->signature != test.signature)
+                {
+                    finding += ", but differently last time";
+                }
+                findings.push_back(finding);
+            }
+            else
+            {
+                test.history = FailureHistory::kNew;
+                std::string finding = "new failure after " +
+                                      std::to_string(past->PassStreak()) +
+                                      " passing run(s)";
+                if (inputs.history != nullptr)
+                {
+                    for (const auto &runRecord : inputs.history->Runs())
+                    {
+                        if (runRecord.id == last->run && !runRecord.commit.empty())
+                        {
+                            finding += "; it last passed at commit " +
+                                       runRecord.commit.substr(0, 12);
+                        }
+                    }
+                }
+                findings.push_back(finding);
+            }
+
+            // Other tests that fail the same way.
+            const auto &group = bySignature[test.signature];
+            if (group.size() > 1)
+            {
+                std::string others;
+                std::size_t named = 0;
+                for (const std::size_t other : group)
+                {
+                    if (other == index)
+                    {
+                        continue;
+                    }
+                    if (named < 3)
+                    {
+                        others += (named > 0 ? ", '" : "'") +
+                                  run.tests[other].name + "'";
+                    }
+                    ++named;
+                }
+                if (named > 3)
+                {
+                    others += " and " + std::to_string(named - 3) + " more";
+                }
+                findings.push_back("fails the same way as " + others +
+                                   ": probably one cause");
+            }
+
+            // Where it stopped.
+            if (failure->outcome == Outcome::kCrashed)
+            {
+                std::string finding = "crashed";
+                if (!failure->exitDescription.empty())
+                {
+                    finding += " (" + failure->exitDescription + ")";
+                }
+                if (!failure->lastLocation.empty())
+                {
+                    finding += " after the assertion at " + failure->lastLocation;
+                }
+                const std::string sections = OpenSections(*failure);
+                if (!sections.empty())
+                {
+                    finding += ", in section " + sections;
+                }
+                findings.push_back(finding);
+            }
+            else if (failure->outcome == Outcome::kTimedOut)
+            {
+                std::string finding =
+                    "stopped after " + Seconds(failure->durationMicroseconds);
+                if (test.predictedDurationMicroseconds > 0 && last != nullptr)
+                {
+                    finding += "; it usually takes " +
+                               Seconds(test.predictedDurationMicroseconds);
+                }
+                const std::string sections = OpenSections(*failure);
+                if (!sections.empty())
+                {
+                    finding += "; it was in section " + sections;
+                }
+                if (!failure->lastLocation.empty())
+                {
+                    finding += "; last assertion started at " +
+                               failure->lastLocation;
+                }
+                findings.push_back(finding);
+            }
+
+            // The change it follows.
+            if (inputs.changes != nullptr)
+            {
+                std::vector<std::string> changedFiles;
+                const auto changed = [&](const std::string &file) {
+                    return std::any_of(inputs.changes->files.begin(),
+                                       inputs.changes->files.end(),
+                                       [&](const auto &path) {
+                                           return SameSourceFile(path, file);
+                                       });
+                };
+                if (changed(test.file))
+                {
+                    changedFiles.push_back(test.file);
+                }
+                for (const auto &assertion : failure->assertions)
+                {
+                    if (!assertion.passed && assertion.file != test.file &&
+                        changed(assertion.file) &&
+                        std::find(changedFiles.begin(),
+                                  changedFiles.end(),
+                                  assertion.file) == changedFiles.end())
+                    {
+                        changedFiles.push_back(assertion.file);
+                    }
+                }
+                for (const auto &file : changedFiles)
+                {
+                    findings.push_back(
+                        "changed since " +
+                        (inputs.changesSince.empty() ? std::string{"HEAD"}
+                                                     : inputs.changesSince) +
+                        ": " + file);
+                }
+            }
+
+            if (!failure->temporaryDirectory.empty())
+            {
+                findings.push_back("its temporary files are kept in " +
+                                   failure->temporaryDirectory);
+            }
+
+            // Findings of the scheduler (order dependence, flakiness,
+            // quarantine) come first.
+            test.analysis.insert(
+                test.analysis.end(), findings.begin(), findings.end());
+
+            std::string replay = QuoteArgument(inputs.program) + " " +
+                                 QuoteArgument(QuoteTestSpec(test.name)) +
+                                 " --seed=" + std::to_string(failure->seed);
+            if (!failure->precededBy.empty() && !test.flaky)
+            {
+                // The replay mode runs the same tests first, in the same
+                // process, as the failure did.
+                replay = QuoteArgument(inputs.program) + " --replay";
+            }
+            test.replayCommand = replay;
+        }
+    }
+} // namespace Progmasoft::Catch3::Runner
diff --git a/src/Progmasoft/Runner/Analysis.hpp b/src/Progmasoft/Runner/Analysis.hpp
new file mode 100644
index 00000000..a39ea8e6
--- /dev/null
+++ b/src/Progmasoft/Runner/Analysis.hpp
@@ -0,0 +1,41 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+#pragma once
+
+#include "Git.hpp"
+#include "History.hpp"
+#include "Planner.hpp"
+
+#include <Progmasoft/Catch3/Results.hpp>
+
+#include <string>
+
+namespace Progmasoft::Catch3::Runner
+{
+    struct AnalysisInputs final
+    {
+        /// The history before this run.
+        const History *history = nullptr;
+        const Changes *changes = nullptr;
+        const Plan *plan = nullptr;
+        /// The binary, for the replay command.
+        std::string program;
+        std::string changesSince;
+    };
+
+    /// Classifies every failure of the run and writes down what the runner
+    /// can tell about its cause: a signature shared with other failures,
+    /// the failure's history, the change it follows, where a crash or a
+    /// hang happened, and a command that replays it.
+    void
+    Analyze(RunResult &run, const AnalysisInputs &inputs);
+
+    /// The signature of a failed attempt: its category, the location of the
+    /// first failure and its message with numbers and addresses replaced.
+    [[nodiscard]] std::string
+    FailureSignature(const Attempt &attempt);
+
+    /// A test spec that matches exactly this name.
+    [[nodiscard]] std::string
+    QuoteTestSpec(const std::string &name);
+} // namespace Progmasoft::Catch3::Runner
diff --git a/src/Progmasoft/Runner/Catalog.cpp b/src/Progmasoft/Runner/Catalog.cpp
new file mode 100644
index 00000000..c34e81e0
--- /dev/null
+++ b/src/Progmasoft/Runner/Catalog.cpp
@@ -0,0 +1,272 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-1.1
+#include <algorithm>
+#include <catch2/catch_test_case_info.hpp>
+#include <catch2/catch_test_spec.hpp>
+#include <catch2/interfaces/catch_interfaces_config.hpp>
+#include <catch2/interfaces/catch_interfaces_registry_hub.hpp>
+#include <catch2/interfaces/catch_interfaces_testcase.hpp>
+#include <catch2/internal/catch_test_case_registry_impl.hpp>
+#include <cmath>
+#include <iterator>
+#include <map>
+
+#include "Catalog.hpp"
+#include "Hash.hpp"
+
+namespace Progmasoft::Catch3::Runner
+{
+    namespace
+    {
+        std::optional<double>
+        ParseSeconds(std::string_view text)
+        {
+            if (text.empty())
+            {
+                return std::nullopt;
+            }
+            double value = 0.0;
+            double scale = 0.0;
+            for (const char character : text)
+            {
+                if (character == '.' && scale <= 0.0)
+                {
+                    scale = 1.0;
+                    continue;
+                }
+                if (character < '0' || character > '9')
+                {
+                    return std::nullopt;
+                }
+                if (scale > 0.0)
+                {
+                    scale /= 10.0;
+                    value += (character - '0') * scale;
+                }
+                else
+                {
+                    value = value * 10.0 + (character - '0');
+                }
+            }
+            return value;
+        }
+
+        bool
+        HasPrefix(std::string_view text, std::string_view prefix)
+        {
+            return text.substr(0, prefix.size()) == prefix;
+        }
+
+        Status
+        ApplyRunnerTag(TestEntry &entry, const std::string &tag)
+        {
+            const auto where = [&] {
+                return "test '" + entry.name + "' at " + entry.file + ":"
+                       + std::to_string(entry.line);
+            };
+            if (tag == "!serial")
+            {
+                entry.serial = true;
+            }
+            else if (tag == "!isolated")
+            {
+                entry.isolated = true;
+            }
+            else if (tag == "!quarantine")
+            {
+                entry.quarantined = true;
+            }
+            else if (HasPrefix(tag, "!resource:"))
+            {
+                entry.resources.push_back(tag.substr(10));
+            }
+            else if (HasPrefix(tag, "!depends:"))
+            {
+                entry.dependsOn.push_back(tag.substr(9));
+            }
+            else if (HasPrefix(tag, "!timeout:"))
+            {
+                const auto seconds = ParseSeconds(tag.substr(9));
+                if (!seconds || *seconds > 1e7)
+                {
+                    return Error{ "[" + tag + "] of " + where()
+                                  + " needs a number of seconds, such as "
+                                    "[!timeout:30]" };
+                }
+                entry.timeout = std::chrono::milliseconds{
+                    static_cast<long long>(std::llround(*seconds * 1000.0))
+                };
+            }
+            else if (HasPrefix(tag, "!retries:"))
+            {
+                const auto count = ParseSeconds(tag.substr(9));
+                if (!count || *count > 100 || std::floor(*count) < *count)
+                {
+                    return Error{ "[" + tag + "] of " + where()
+                                  + " needs a whole number up to 100, such as "
+                                    "[!retries:3]" };
+                }
+                entry.retries = static_cast<unsigned>(*count);
+            }
+            return Status::Ok();
+        }
+    } // namespace
+
+    Expected<Catalog>
+    Catalog::Load()
+    {
+        Catalog catalog;
+        const auto &handles
+            = Catch::getRegistryHub().getTestCaseRegistry().getAllTests();
+        catalog.handles_ = handles;
+        // Two tests with the same class, name and tags cannot be told apart
+        // by any filter, history record or report, so they are refused.
+        std::vector<const Catch::TestCaseInfo *> sorted;
+        sorted.reserve(handles.size());
+        for (const auto &handle : handles)
+        {