test runner, cross-target runners, lib/exe split

- subprocess-isolated test runner (replaces V1 dlopen-RunTest);
  Pass/Fail/Crash/Timeout/Skipped outcomes via :Test partition
- TestRunner abstraction with command templates: Local, Ssh,
  SshWin (cmd.exe-shell), QemuUser, FromEnv; probe-based skip
  when runner unreachable
- transitive PCM-path propagation in Build(); resolveImport
  walks deps recursively; depResults cache keyed by PcmDir()
  so per-target builds don't collide
- cfg.sysroot threaded through BuildStdPcm + base compile/link
  command (enables aarch64 cross via Arch Linux ARM rootfs)
- lib + exe split: project.cpp defines crafterBuildLib
  (LibraryStatic) + crafterBuildExe (Executable depending on
  it); build.sh produces lib/libcrafter-build.a alongside
  bin/crafter-build for downstream static-link consumers
- Windows DLL+launcher: CRAFTER_API macro, /EXPORT flag for
  project.dll's CrafterBuildProject; Crafter::Run as the real
  entry point with main.cpp as a thin wrapper
- 18 tests: HelloWorld/WithModule/Defines/CrossProjectModule/
  Diamond × (Linux + sshwin:winvm), plus Incremental,
  BuildError, Libraries, RunnerClassification, QemuUser,
  SshRunner, WindowsViaSsh, CrossArchAarch64
- single ./bin/crafter-build test runs everything; Windows
  variants skip gracefully if winvm SSH alias unreachable

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/Incremental.cpp

@@ -0,0 +1,76 @@
+/*
+Crafter® Build
+Copyright (C) 2026 Catcrafts®
+Catcrafts.net
+
+LGPL-3.0-only.
+*/
+
+import std;
+#include "TestUtil.h"
+namespace fs = std::filesystem;
+using namespace std::chrono_literals;
+using namespace TestUtil;
+
+int main() {
+    try {
+        fs::path projectRoot = fs::current_path();
+        fs::path src = projectRoot / "tests" / "fixtures" / "incremental";
+        fs::path crafterBuild = projectRoot / "bin" / "crafter-build";
+
+        fs::path work = CopyFixtureToTemp("Incremental", src);
+        fs::path buildDir = work / "build" / "hello-mod-x86_64-pc-linux-gnu-native";
+        fs::path greeterObj = buildDir / "Greeter.o";
+        fs::path mainObj = buildDir / "main_impl.o";
+        std::string buildCmd = std::format("'{}'", crafterBuild.string());
+
+        // 1. cold build
+        if (auto r = RunInDir(work, buildCmd); r.exitCode != 0) {
+            std::println(std::cerr, "cold build failed (rc={}):\n{}", r.exitCode, r.output);
+            return 1;
+        }
+        if (!fs::exists(greeterObj) || !fs::exists(mainObj)) {
+            std::println(std::cerr, "expected .o files missing after cold build");
+            return 1;
+        }
+        auto greeter_t1 = fs::last_write_time(greeterObj);
+        auto main_t1    = fs::last_write_time(mainObj);
+
+        // 2. no-op rebuild: nothing should be regenerated
+        if (auto r = RunInDir(work, buildCmd); r.exitCode != 0) {
+            std::println(std::cerr, "no-op rebuild failed (rc={}):\n{}", r.exitCode, r.output);
+            return 1;
+        }
+        auto greeter_t2 = fs::last_write_time(greeterObj);
+        auto main_t2    = fs::last_write_time(mainObj);
+        if (greeter_t2 != greeter_t1) {
+            std::println(std::cerr, "no-op rebuild regenerated Greeter.o");
+            return 1;
+        }
+        if (main_t2 != main_t1) {
+            std::println(std::cerr, "no-op rebuild regenerated main_impl.o");
+            return 1;
+        }
+
+        // 3. touch main.cpp: only main_impl.o should regenerate
+        fs::last_write_time(work / "main.cpp", std::chrono::file_clock::now() + 2s);
+        if (auto r = RunInDir(work, buildCmd); r.exitCode != 0) {
+            std::println(std::cerr, "rebuild after touch failed (rc={}):\n{}", r.exitCode, r.output);
+            return 1;
+        }
+        auto greeter_t3 = fs::last_write_time(greeterObj);
+        auto main_t3    = fs::last_write_time(mainObj);
+        if (greeter_t3 != greeter_t1) {
+            std::println(std::cerr, "touching main.cpp unnecessarily rebuilt Greeter.o");
+            return 1;
+        }
+        if (main_t3 <= main_t1) {
+            std::println(std::cerr, "touching main.cpp did NOT rebuild main_impl.o");
+            return 1;
+        }
+        return 0;
+    } catch (const std::exception& e) {
+        std::println(std::cerr, "test exception: {}", e.what());
+        return 1;
+    }
+}