Send a static shell that needs runtime data straight to runtime
Under Partial Prefetching a task fills until the entry is cache complete. A
static shell whose own runtime-data flag says it read runtime data means the
later stages read it too, so a static prefetch can't complete it; only a
runtime prefetch can. Such an entry now skips the static attempt and goes
straight to the runtime request. A runtime shell is still eligible: it is
cache complete at the shell stage, and a static attempt may be enough for
the later stages when the server's hint says so.
