feat: add v2 task control and asynchronous isolated workers

include/cst_worktree.h

@@ -0,0 +1,16 @@
+#ifndef CST_WORKTREE_H
+#define CST_WORKTREE_H
+#include <stddef.h>
+#ifdef __cplusplus
+extern "C" {
+#endif
+/* files is a JSON array of workspace-relative paths. No caller index changes. */
+int cst_worktree_create(const char *workspace, const char *files, char *out,
+                        size_t out_sz, char *err, size_t err_sz);
+char *cst_worktree_diff(const char *workspace, const char *worktree, int integrate,
+                        int *code);
+int cst_worktree_path_allowed(const char *files, const char *relative_path);
+#ifdef __cplusplus
+}
+#endif
+#endif