Codex regression gate (+Opus, both independently) found the default-only guard
dropped the stale compressor cap but two sibling paths stayed inconsistent:
1. Per-turn persistence: fallback resolver only ran when context_length was
falsy, so a previously-persisted stale 232K survived forever on non-default
sessions. Now also runs when _skip_cc_cl, and rescales threshold_tokens to
the recomputed real cap (or clears it).
2. Terminal SSE 'done' payload: re-emitted the stale compressor threshold, so
messages.js overwrote S.lastUsage and the indicator reverted on stream end.
Now rescales threshold to the resolved window when the stale cap was dropped.
Added 3 source-structure regression tests pinning both fixes; bumped the brittle
test_pr1341 distance limit 13000→15000 (+ noted it should become structural).
Co-authored-by: allenliang2022 <allenliang2022@users.noreply.github.com>
