Realign undo with the evening rulings — repo-nested and identity anchors

Repo-nested boards bind native undo in every tier (25d2513): the
no-undo case is gone, makeHistoryProvider answers git or native, and
the native path provably never touches the enclosing repository's
.git. Session undo steps anchor by card identity, never by path
(9119aa1): HistoryAnchor carries the card UUID (plus comment/draft
vocabulary) and apply-time validation resolves the current folder via
the same both-container walk writeCardBody uses — a board-side lane or
trash move no longer stales the coarse close step, while a genuine
field collision still skips it whole.

2448 tests in 423 suites green.

Claude-Session: https://claude.ai/code/session_01CqjXB7ASoWtbyoGod68k97

Kanban/Git/HistoryStore.swift

@@ -20,11 +20,12 @@ import os
 ///
 /// This is the foundation card of pro-m1: mode, a repository, add-git, and the loader's path-history
 /// ranker. **The provider binding reads `mode` and nothing else about a tier** — the composition
-/// root binds the git provider on mode `git`, the native stack on mode `none`, and nothing on a
-/// repo-nested board (`AppModel.makeHistoryProvider`, re-ruled 2026-07-31: the provider follows the
-/// board). Auto-commit, commit messages, branch controls, the identity fields, the
-/// `.gitignore` seed and its periodic housekeeping each arrived as their own card and are composed
-/// here now; remotes are pro-m2's and deliberately still absent.
+/// root binds the git provider on mode `git` and the native stack on modes `none` and `repoNested`
+/// alike (`AppModel.makeHistoryProvider`, re-ruled 2026-07-31: the provider follows the board, and
+/// what a repo-nested board denies is app-managed history, never ⌘Z). Auto-commit, commit messages,
+/// branch controls, the identity fields, the `.gitignore` seed and its periodic housekeeping each
+/// arrived as their own card and are composed here now; remotes are pro-m2's and deliberately still
+/// absent.
 @MainActor
 @Observable
 public final class HistoryStore {