The tier axis comes out of the git stack — compose unconditional, postures mode-driven

HistoryStore.compose(boardRoot📒) returns non-optional and runs for
every session — the nil the gate produced was the only nil it ever had.
makeHistoryProvider is a one-axis decision: git-mode boards bind the git
provider, everything else native, in every tier; Session.tier stays
recorded, dormant. BoardGitSection shrinks to the four mode postures
(.absent and .proPointer die, BoardGitNote and the .git probe with them);
every board carries all three popover tabs (BoardInfoTab.available
retired); the titlebar branch shows on any git-mode board; the settings
sheet and card History section stop reading tier. InertGitTests is
repurposed as UntouchedGitTests — the file layer still never opens .git,
now load-bearing for mode-none boards. The accessibility audit reaches the
settings sheet at last: the fixture board hosts it in every tier, so the
free-fixture disabled-row test becomes an open-and-audit test.

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

Kanban/Git/GitHistoryProvider.swift

@@ -254,13 +254,15 @@ public final class GitHistoryProvider: HistoryProviding {
     // MARK: - HistoryProviding
 
     /// **Deliberately nothing — except the one thing a dropped step is owed.** On a git board an undo
-    /// step is a commit, and the Writer boundary's inverse operations are the *free* tier's substrate
-    /// (13-native-undo.md). `BoardStore` registers against whatever provider the session bound, and
+    /// step is a commit, and the Writer boundary's inverse operations are the *gitless* board's
+    /// substrate (13-native-undo.md — the tier axis it once read as went with 12-editions.md
+    /// ▸ PIVOT 2026-08-07; the substrate is the board's mode alone). `BoardStore` registers against
+    /// whatever provider the session bound, and
     /// this one has a repository to read instead — so the registrations arrive and are dropped, which
     /// is exactly what "the commit trail itself is the substrate" (14 ▸ C1) means in code.
     ///
     /// Dropping a step means **retiring** it (`HistoryStep.Retirement`), and that is what keeps the
-    /// tier split in 13's purge rule structural rather than conditional: "on Pro the substrate is
+    /// substrate split in 13's purge rule structural rather than conditional: "on Pro the substrate is
     /// history: the close commit nets delete-plus-purge to a removal, revert restores it, so purge
     /// rides the close flush there as before" (13 ▸ Interaction with the trash). A card window's close
     /// step registered here is retired on arrival, so its deferred `comments/.trash/` purge runs