cut: schema gate — refuse to release an undisclosed querylog schema change

the gate recomputes the previous release tag's ddl fingerprint from the
remote peeled object and compares it against the tree's; a change must
be disclosed by 'resets your query history' in the version's changelog
section. the 0.0.9 reset shipped with an announcement claiming no
schema change; this makes the impact mechanical instead of remembered.

CHANGELOG.md

@@ -4,6 +4,12 @@ All notable changes to nxdns are recorded here. The format follows [Keep a Chang
 
 Sections are written by hand. Nothing here is generated from commit messages: the point of the file is to say what changed for an operator, which a commit subject rarely does.
 
+## [Unreleased]
+
+### Changed
+
+- **The release cut refuses to ship an undisclosed query-log schema change.** `zig build cut` now compares the `querylog.db` schema fingerprint of the previous release tag against this tree's, and when they differ it requires the changelog section for the version being cut to state that the upgrade discards the stored query history. 0.0.9 changed the schema and its announcement did not mention it; the file is never migrated, so that upgrade silently threw every logged query away.
+
 ## [0.0.9] - 2026-08-22
 
 Query provenance: every logged query becomes exactly explainable — what the policy decided, what matched, where the answer came from and what the client saw. The handler records all of it as the reply goes out, `query_log` stores it, and a detail page reads one query back in the order the pipeline decided it. Read the upgrade note below first: it resets your query history.