In an A<->B cycle, exportsFor(B) run while A is mid-resolution would
compute a wrong export set (assignments dropped by the nested
"circular reference" error) and cache it anyway. Later queries then
served that stale, cycle-broken result even after the cycle-causing
outer call had unwound, giving inconsistent error messages across
repeated evaluations of the same cyclic setup.
Skip caching whenever any line in the result carries a "circular
reference" error - that's a precise, local signal the pass was
cycle-affected, so the sheet gets re-evaluated fresh until an edit
actually breaks the cycle. Normal (non-cyclic) caching is untouched.
Also adds a positive-path test confirming LineResult.error stays
undefined on an ordinary successful line, and a workspace-level test
proving a genuine cycle now reports a stable error across repeated
queries.
