Comments, phase 1 — storage, writer primitives, and the undo inventory

The kind: comment field table lands in IntegrityRules (the per-kind
hook's first exercise), CommentThread reads one card's thread
window-scoped (the board walk stays O(cards)), and CommentWriter gains
the five gestures: draft save, post (rename .draft to a fresh UUID,
created/modified restamped in the bracket), edit, delete into
comments/.trash/, and the purge with its crash-residue memo. Post and
delete register move-based undo steps; draft saves, edits, and the
purge deliberately register nothing (13's no-capture rule). Copy
boundaries strip comments/.trash, carry .draft verbatim, and remint
threads; comments graduates to a displacing claimed name, with .draft,
.trash, and a comment's attachments claimed one level down.
CommentPath classifies changed paths into the 06 verb family for
later announcer/composer wiring.

One stated narrowing pending a ruling (filed on the findings board):
the copy transaction's refuse-whole preflight stays cards-and-lanes —
an unstampable copied comment copies verbatim with a log line, because
comment defects never refuse.

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY

Kanban/Storage/BoardLoader.swift

@@ -376,9 +376,10 @@ public enum BoardLoader: Sendable {
                     heldCards: children().count,
                     document: document
                 ))
-            case .card, .board:
-                // `kind: board` never reaches here as itself — `trashKind` treats it as unrecognized
-                // and answers by shape — so this arm is the card answer and nothing else.
+            case .card, .board, .comment:
+                // Neither `kind: board` nor `kind: comment` reaches here as itself — `trashKind`
+                // treats both as unrecognized and answers by shape — so this arm is the card answer
+                // and nothing else.
                 trash.append(Card(
                     id: id,
                     schema: schema,