feat(tooling): wire consumers in through Debug::Use and a launcher

A consumer loads Crafter.Debug.Build through
  #pragma crafter dependency "<Crafter.Debug>" project "tooling/project.cpp"
and calls Debug::Use in its own CrafterBuildProject, the way
Crafter.LintRules gets in. With the consumer's flag on, Use adds the
library from the checkout the pragma loaded, and writes
build/crafter-debug: a POSIX sh launcher for the client that library
builds. The client is one of the library's dependencies, so a debug
build compiles it in the same pass as the app, from the same sources.

Why a launcher and not a script: every `crafter-build run` loads the
whole project first, which costs 13-28 s per call on 3DForts (a git
pull per unpinned dependency plus rescanning sources), while the
launcher is one sandbox start, 0.08 s. A client built in the Flatpak
links the Flatpak's libc++ against the runtime's glibc, so the launcher
starts it through `flatpak run` and never on the host itself; inside a
CrafterBuild sandbox it runs it directly.

The library, the client and examples/Basic are placeholders that prove
the wiring: the debug build writes a launcher whose client exists, a
plain build has no Crafter::Debug symbols and keeps the notes from
tooling/AGENTS.consumer.md, and a fresh plain build writes a stub that
names the flag.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/Basic/AGENTS.template.md

@@ -0,0 +1,3 @@
+# Basic
+
+A Crafter.Debug example. Build with `crafter-build --debug-api` to include the debug server.

examples/Basic/CLAUDE.md

@@ -0,0 +1 @@
+@AGENTS.md

examples/Basic/implementations/main.cpp

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+import std;
+#ifdef BASIC_DEBUG_API
+import Crafter.Debug;
+#endif
+
+int main() {
+#ifdef BASIC_DEBUG_API
+    std::println("basic: debug build, Crafter.Debug {}", Crafter::Debug::Version());
+#else
+    std::println("basic: plain build");
+#endif
+    return 0;
+}

examples/Basic/project.cpp

@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+import std;
+import Crafter.Build;
+// This checkout's own build helper. A consumer elsewhere names the repository:
+//   #pragma crafter dependency "https://forgejo.catcrafts.net/Catcrafts/Crafter.Debug.git" project "tooling/project.cpp"
+#pragma crafter dependency "../.." project "tooling/project.cpp"
+import Crafter.Debug.Build;
+namespace fs = std::filesystem;
+using namespace Crafter;
+
+extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> args) {
+    Configuration cfg;
+    cfg.path = "./";
+    cfg.name = "Basic";
+    cfg.outputName = "basic";
+    cfg.type = ConfigurationType::Executable;
+    const ArgQuery opts = ApplyStandardArgs(cfg, args);
+
+    // What every dependency gets: this project's args minus the flags only it
+    // reads. A dependency that two paths share must get one list on both.
+    std::vector<std::string> depArgs;
+    for (const std::string_view arg : args) {
+        if (arg != "--debug-api") depArgs.emplace_back(arg);
+    }
+    Debug::Use(cfg, { .enabled = opts.Has("--debug-api"), .flag = "--debug-api", .define = "BASIC_DEBUG_API", .args = depArgs });
+
+    std::array<fs::path, 0> interfaces = {};
+    std::array<fs::path, 1> implementations = { "implementations/main" };
+    cfg.GetInterfacesAndImplementations(interfaces, implementations);
+    return cfg;
+}