docs: handoff-77, changelog-discipline rule, and #39 changelog entry

- docs/handoff/20260622-handoff-77.md — session handoff for the #39
  schema-cache-gate fix; records the four open issues (incl. the new #40).
- CLAUDE.md — add the changelog-discipline rule: update [Unreleased] in
  the same change as any user-facing behaviour change (scripted/pasted
  paths count), under the two copy rules; release-time sweep of
  commits/handoffs as the backstop.
- CHANGELOG.md — [Unreleased] → Fixed bullet for the #39 paste/scripted-
  input fix.

CHANGELOG.md

@@ -18,6 +18,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   on each build.
 
 ### Fixed
+- Pasting or scripting several commands at once no longer occasionally
+  rejects a valid simple-mode `insert` — submitted right after adding a
+  column — as though it were advanced-mode SQL.
 - **Light theme:** string-literal and flag colours in syntax highlighting
   were below the WCAG-AA contrast bar; both are now legible. Two dark-theme
   token colours that were hard to tell apart have been separated.