Merge branch 'claude/dependency-notes': a library's AGENTS.consumer.md in its consumers' AGENTS.md

Brings in dependency notes: a crafter-build project that ships an
AGENTS.consumer.md beside its project.cpp has it kept in a marked
section of each consumer's AGENTS.md, refreshed by `crafter-build` and
`crafter-build test`, chosen by cfg.dependencyNotes (Transitive,
Direct, None). The new partition is Crafter.Build:Agents; the loader
records where each GitProject and LocalProject came from and what a
project file's pragmas resolved to.

The branch started before master's four external-fetch commits. Both
touch External.cpp, the Clang partition, project.cpp, README.md and
AGENTS.md, but in different places, so the merge needed no hand
reconciliation; the merged tree passes build.sh, the self-host build,
format --check and the test suite.

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

implementations/Crafter.Build-External.cpp

@@ -324,6 +324,10 @@ ExternalBuildResult Crafter::ExternalOutputs(const ExternalDependency& dep, std:
 namespace {
     std::mutex ProjectCacheMutex;
     std::unordered_map<std::string, std::unique_ptr<Configuration>> ProjectCache;
+    // Keyed by the Configurations ProjectCache owns, which live as long as
+    // the process does, so the pointers never dangle. Guarded by
+    // ProjectCacheMutex as well.
+    std::unordered_map<const Configuration*, LoadedProject> LoadedProjects;
 
     // Run the dep's project.cpp from its own directory so its relative paths
     // (cfg.path = "./", interfaces/, lib/, ...) resolve against the dep
@@ -353,6 +357,36 @@ namespace {
         for (Shader& s : cfg.shaders)   s.path = abs(s.path);
         return cfg;
     }
+
+    // Into ProjectCache under `fullHash`, with `loaded` recorded beside it.
+    // When another thread stored the same spec first, its Configuration
+    // wins and `cfg` is dropped.
+    Configuration* StoreProject(std::string fullHash, Configuration cfg, LoadedProject loaded) {
+        std::lock_guard lock(ProjectCacheMutex);
+        if (auto it = ProjectCache.find(fullHash); it != ProjectCache.end()) {
+            return it->second.get();
+        }
+        auto stored = std::make_unique<Configuration>(std::move(cfg));
+        Configuration* ptr = stored.get();
+        ProjectCache.emplace(std::move(fullHash), std::move(stored));
+        LoadedProjects.emplace(ptr, std::move(loaded));
+        return ptr;
+    }
+
+    // `url` as it names a repository: without user info, which is where a
+    // token goes, and without trailing slashes or ".git", so specs that only
+    // spell the repository differently name the same one.
+    std::string RepositoryKey(std::string_view url) {
+        std::string key(url);
+        if (const std::size_t scheme = key.find("://"); scheme != std::string::npos) {
+            const std::size_t host = scheme + 3;
+            const std::size_t at = key.rfind('@', key.find('/', host));
+            if (at != std::string::npos && at >= host) key.erase(host, at + 1 - host);
+        }
+        while (key.ends_with('/')) key.pop_back();
+        if (key.ends_with(".git")) key.resize(key.size() - 4);
+        return key;
+    }
 }
 
 Configuration* Crafter::GitProject(const GitProjectSpec& spec) {
@@ -405,14 +439,13 @@ Configuration* Crafter::GitProject(const GitProjectSpec& spec) {
     std::vector<std::string_view> argViews(spec.args.begin(), spec.args.end());
     Configuration cfg = LoadProjectFromRoot(projectPath, cloneDir, argViews);
 
-    std::lock_guard lock(ProjectCacheMutex);
-    if (auto it = ProjectCache.find(fullHash); it != ProjectCache.end()) {
-        return it->second.get();
-    }
-    auto stored = std::make_unique<Configuration>(std::move(cfg));
-    Configuration* ptr = stored.get();
-    ProjectCache.emplace(std::move(fullHash), std::move(stored));
-    return ptr;
+    const fs::path projectInRepo = spec.projectFile.lexically_normal();
+    const fs::path below = projectInRepo.parent_path();
+    return StoreProject(std::move(fullHash), std::move(cfg), {
+        .projectFile = projectPath.lexically_normal(),
+        .name = below.empty() ? name : std::format("{}/{}", name, below.generic_string()),
+        .identity = std::format("git|{}|{}", RepositoryKey(spec.source.url), projectInRepo.generic_string()),
+    });
 }
 
 fs::path Crafter::GitFetch(const GitSource& source) {
@@ -467,12 +500,15 @@ Configuration* Crafter::LocalProject(const LocalProjectSpec& spec) {
     std::vector<std::string_view> argViews(spec.args.begin(), spec.args.end());
     Configuration cfg = LoadProjectFromRoot(canonical, depRoot, argViews);
 
-    std::lock_guard lock(ProjectCacheMutex);
-    if (auto it = ProjectCache.find(fullHash); it != ProjectCache.end()) {
-        return it->second.get();
-    }
-    auto stored = std::make_unique<Configuration>(std::move(cfg));
-    Configuration* ptr = stored.get();
-    ProjectCache.emplace(std::move(fullHash), std::move(stored));
-    return ptr;
+    return StoreProject(std::move(fullHash), std::move(cfg), {
+        .projectFile = canonical,
+        .name = depRoot.filename().string(),
+        .identity = std::format("local|{}", canonical.string()),
+    });
+}
+
+std::optional<LoadedProject> Crafter::LoadedProjectOf(const Configuration& cfg) {
+    std::lock_guard lock(ProjectCacheMutex);
+    if (auto it = LoadedProjects.find(&cfg); it != LoadedProjects.end()) return it->second;
+    return std::nullopt;
 }