diff --git a/DESIGN/06-history-undo.md b/DESIGN/06-history-undo.md
index 4aae37d..32afc30 100644
--- a/DESIGN/06-history-undo.md
+++ b/DESIGN/06-history-undo.md
@@ -72,7 +72,7 @@ Agent and hand edits arrive through the watcher like any change and get auto-com
 ## Repository hygiene
 
 - **`.gitignore` seeded at init, never touched after.** Adding git to a board writes a minimal `.gitignore` (`.DS_Store`) if none exists; the app never edits an existing one and never manages the file afterward — it's the user's from then on. (Repo-nested boards have no app-managed git, so no app `.gitignore` either.)
-- **Repo growth is accepted.** Unbounded history is the price of never-rewrite, and every attachment version lives in the repo forever. The app may run safe libgit2 housekeeping (repacking loose objects) periodically — it rewrites nothing. **"Periodically" has numbers** (blessed 2026-07-31, all injectable): the pack runs when the loose-object count crosses **6,700** — git's own `gc.auto` default, borrowed for the identical reason — **8 s after session activation** (outlasting the committer's launch catch-up), at background priority, skipped under a pause, a lock, or an in-flight commit, and **attempted at most once per session** — hygiene must never become a hot loop; a skipped or failed pack waits for the next open. **Packs accumulate — the pass never consolidates, rewrites, or deletes existing packs** (blessed 2026-07-31): it deletes only loose files it proved redundant against the pack it just wrote, so a long-lived board accrues roughly one pack per threshold's worth of objects, forever — the never-rewrite posture's accepted cost (git tolerates many packs gracefully; a terminal `git gc` consolidates at the user's discretion). Content-removing compaction is explicitly out (it would rewrite history); size tooling joins the wishlist if growth ever bites in practice.
+- **Repo growth is accepted.** Unbounded history is the price of never-rewrite, and every attachment version lives in the repo forever. The app may run safe libgit2 housekeeping (repacking loose objects) periodically — it rewrites nothing. **"Periodically" has numbers** (blessed 2026-07-31, all injectable): the pack runs when the loose-object count crosses **6,700** — git's own `gc.auto` default, borrowed for the identical reason — **8 s after session activation** (outlasting the committer's launch catch-up), at background priority, skipped under a pause, a lock, or an in-flight commit, and **attempted at most once per session** — hygiene must never become a hot loop; a skipped or failed pack waits for the next open. **Packs accumulate — the pass never consolidates, rewrites, or deletes existing packs** (blessed 2026-07-31): it deletes only loose files it proved redundant against the pack it just wrote, so a long-lived board accrues roughly one pack per threshold's worth of objects, forever — the never-rewrite posture's accepted cost (git tolerates many packs gracefully; a terminal `git gc` consolidates at the user's discretion). **SHA-256 repositories are unsupported, safely** (blessed 2026-07-31): an adopted SHA-256 repo the engine cannot open takes the corrupt-repo loud-failure path — never a silent fall to mode-none; should one ever open, hygiene abstains by construction — its loose-object filter matches the SHA-1 filename shape only, so its work list is empty and the repo is left untouched (recognizing nothing and touching nothing is the fail-safe direction; a looser match that deleted half-recognized files would be the dangerous one). Content-removing compaction is explicitly out (it would rewrite history); size tooling joins the wishlist if growth ever bites in practice.
 - **Deleting never forgets.** On a git board, deleting a card removes it from the board but never from history — every version of its content and attachments stays reachable in any git client, and even a trash purge (Empty Trash, or the future age-based auto-purge — 01-storage-format.md) only cleans the working tree. This is part of the design; users should learn it here, not from a repo browser.
 
 ## Changes from Kanban