Function heap_strdup

src/graph_buffer/graph_buffer.c:122–124

/* ── Helpers ─────────────────────────────────────────────────────── */

static char *heap_strdup(const char *s) {
    return s ? strdup(s) : strdup("{}");
}

/* Intern a repetitive string into the buffer's pool: identical content collapses
 * to a single heap copy owned by the pool. NULL maps to "{}" (matches