Remove the App Group wholesale — one sandbox, one bookmark, one flag

Phase 2 of the one-app pivot (DESIGN 12 ▸ App-side state, re-ruled
2026-07-30; reworks 566deab). AppGroup retires; what remains is
AppStateHome — ordinary sandbox Application Support as the one home for
the registry, clipboard staging and template stores, keeping the
unit-test-host redirect (the test host is the app and would sweep real
state). Scalar defaults return to UserDefaults.standard.

BoardRecord's per-edition grant slots and openNow flags collapse to one
bookmark + one isOpenNow; the legacy-key decode and adopt-in-memory
paths go (nothing shipped with group-era records), while the founding
four-keys-required / defaults-for-everything-since decode policy stays —
a bookmarkless record decodes as the born-orphan row rather than
quarantining the list. needsReopen and the pre-anchored re-grant panel
are removed whole: the only state that flow served — a record granted by
a sibling sandbox — is unrepresentable now, and a dead bookmark of our
own was already the orphan case by explicit comment. The
indexOfRecord path fallback dies with it; path is never a key again.

The cross-process freshness stamp (mtime+size re-read) and
BoardEditionPresence with its popover "Also open in…" line retire; the
clipboard prune keeps its atomic .sweeping/ claim-then-delete, reframed
for crash residue and open -n copies rather than sibling editions. The
application-groups entitlement key is gone.

1880 tests in 317 suites green (13 cross-edition tests retired with
their subject).

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

Kanban/Kanban.entitlements

@@ -18,15 +18,9 @@
 	     credentials go to the sandbox's own keychain, which needs no key at all. -->
 	<key>com.apple.security.network.client</key>
 	<true/>
-	<!-- The App Group, on borrowed time. 12-editions.md ▸ App-side state (re-ruled 2026-07-30)
-	     removes it wholesale — the board registry and its Application Support peers home in the
-	     ordinary sandbox container once there is one app — but the removal is the *code's* to
-	     make, not this file's: `AppGroup.swift` still resolves its container through this key,
-	     and pulling it first would silently drop the app into the fallback home. It goes with
-	     that code. -->
-	<key>com.apple.security.application-groups</key>
-	<array>
-		<string>group.dev.rzen.indie.Kanban</string>
-	</array>
+	<!-- No `com.apple.security.application-groups`: a group exists to share a container *between*
+	     apps, and there is one app (12-editions.md ▸ App-side state, re-ruled 2026-07-30). The
+	     board registry and its Application Support peers home in the ordinary sandbox container
+	     (`AppStateHome`), which the sandbox already scopes to this app alone. -->
 </dict>
 </plist>