feat: Rust std target + ruststd tests; SYS_EXIT_GROUP; fix mkdir/create under missing parent

kernel/src/Fs/Ramdisk.cpp

@@ -89,6 +89,20 @@ namespace Fs::Ramdisk {
         return -1;
     }
 
+    // Mkdir/Create must not conjure entries under a missing parent: the
+    // table is flat, so "a/b/" with no "a/" entry is invisible to ReadDir of
+    // the parent and makes "a" fail Stat, Delete and recursive removal.
+    static bool ParentExists(const char* path) {
+        char normalized[MaxNameLen];
+        int len = NormalizePath(path, normalized, MaxNameLen);
+        if (len < 0) return false;
+        while (len > 0 && normalized[len - 1] != '/') len--;
+        if (len <= 1) return true;  // parent is the root
+        normalized[len - 1] = '\0';
+        int idx = FindEntryByPath(normalized);
+        return idx >= 0 && fileTable[idx].isDirectory;
+    }
+
     void Initialize(void* moduleData, uint64_t moduleSize) {
         Kt::KernelLogStream(Kt::OK, "Ramdisk") << "Parsing USTAR archive (" << moduleSize << " bytes)";
 
@@ -442,6 +456,8 @@ namespace Fs::Ramdisk {
             }
         }
 
+        if (!ParentExists(path)) return -1;
+
         // Create new file entry
         FileEntry& entry = fileTable[fileCount];
 
@@ -531,6 +547,8 @@ namespace Fs::Ramdisk {
             }
         }
 
+        if (!ParentExists(path)) return -1;
+
         // Create directory entry (stored with trailing slash for tar convention)
         FileEntry& entry = fileTable[fileCount];