-- pg_tre 1.5.5 -> 1.5.6 upgrade.
--
-- No catalog changes: 1.5.6 is a C-level robustness + DoS-hardening
-- release.
--
--   * Pending-list merge now descends a MULTI-LEVEL upper tree.  Once an
--     index accumulated enough distinct trigrams for VACUUM to build an
--     upper internal page (page_kind=2) fanning out to many upper
--     leaves, the prior pending merge could read back only a single
--     upper leaf and raised "pending-list merge on multi-level upper
--     tree not yet supported" (HINT: REINDEX).  The merge snapshot now
--     recurses the whole upper subtree, so subsequent inserts merge
--     cleanly with no REINDEX.
--   * materialize_merged_postings no longer probes every integer in the
--     TID range with sm_contains (an O(TID-range) loop that spun ~100%
--     CPU for minutes on wide-spanning trigrams); it iterates members in
--     rank order via sm_next_member instead.
--   * pg_tre.compile_timeout_ms is now ENFORCED: a real wall-clock
--     deadline armed around regex compilation (progress hook woven into
--     TRE's NFA-build loops) aborts pathological compiles with a
--     query_canceled error.  Previously the GUC was defined but never
--     honored.
--
-- No on-disk format change (remains v5); no REINDEX required.  This
-- upgrade script is an intentional no-op that only bumps the recorded
-- extension version.