v0.254.0 — the saved notes follow the language, and the switch becomes a globe (R-557 slice 2 release C; SLICE 2 CLOSED)

The notes a background run SAVES — last night's backup line, the last error, the proof
result, the restore outcome — are written in the BOX's language at the moment they are
written. A household that switches sees the previous run's note in the old language until
the next run rewrites it: the operator's §16 option 1, stated rather than hidden.
EndRestoreOp no longer receives a Hungarian literal from anywhere.

The language switch is a globe. Two text links wrapped in the sidebar footer and asked the
reader to recognise "Magyar"/"English" as links; a globe is the one symbol every web user
already reads as "language", so nobody has to read Hungarian to escape Hungarian. It is
<details>/<summary> — a menu with no script, drawn inline because the icon sprite lives
only in layout.html and the visitor pages have their own shell.

Those visitor pages get the same globe, and a visitor's choice stays theirs: a display-only
felhom_lang cookie that langFor reads ONLY when there is no session. A signed-in household
can never inherit a language a previous visitor picked in the same browser. POST /lang is
CSRF-exempt for a narrow reason written at the exemption — its only achievable effect is the
language of the page the victim's own browser shows them — and safeBackPath refuses
//evil.example as well as https://, because "starts with /" alone is not the test. §16 taken:
a successful claim carries the cookie into the household's setting.

TWO PARITY EXCEPTIONS, MEASURED: 106 fixtures compared with a real diff — exactly two change
shapes (the dashboard footer, the globe in the shells) and 5 byte-identical, which are the
three pages that must not change.

I INTRODUCED A DEADLOCK AND THE SUITE CAUGHT IT BY HANGING. UpdateOffboxStatus holds the
settings write lock while running its callback; boxLang() wants the read lock; sync.RWMutex
is not reentrant. On a real box an off-site run would have hung forever HOLDING the settings
lock. Fixed by resolving the language before the callback, and guarded by a test that names
the file and line in a second instead of hanging for 25 minutes.

MinAgent: 0.131.0 (unchanged). No hub release needed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/backup/r383_undo_phrase_test.go

@@ -86,7 +86,7 @@ func TestR383_AbsentUndoCopyIsNotClaimedToExist(t *testing.T) {
 	}
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {
-			got := undoCopyPhrase(tc.set)
+			got := newNoteManager(t).undoCopyPhrase(tc.set)
 			for _, want := range tc.mustContain {
 				if !strings.Contains(got, want) {
 					t.Errorf("phrase %q does not contain %q", got, want)
@@ -119,9 +119,16 @@ func TestR383_TheDoubleFailureMessageIsWiredToTheBuilder(t *testing.T) {
 		}
 		switch fn := call.Fun.(type) {
 		case *ast.SelectorExpr:
+			// v0.254.0 (R-557 release C): undoCopyPhrase became a METHOD, because a saved note is
+			// rendered in the box's language and that needs the Manager. A method call is a
+			// SelectorExpr, not an Ident — so it is matched here as well as below, and the test keeps
+			// asserting what it always asserted rather than passing because the shape moved.
 			if fn.Sel.Name == "holdAppAfterFailedRollback" {
 				holdCalled = true
 			}
+			if fn.Sel.Name == "undoCopyPhrase" {
+				phraseCalled = true
+			}
 		case *ast.Ident:
 			if fn.Name == "undoCopyPhrase" {
 				phraseCalled = true