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/r403_mirror_guard_test.go

@@ -216,9 +216,12 @@ func TestR403_SkipIsRecordedForTheSurface(t *testing.T) {
 	if !strings.Contains(cd.LastWarning, "hi") { // ASCII fragment of "hiányos" (R-364)
 		t.Errorf("LastWarning does not carry the preserved-copy notice: %q", cd.LastWarning)
 	}
-	if cd.LastWarning != tier2UnitPreservedWarning &&
-		!strings.Contains(cd.LastWarning, tier2UnitPreservedWarning) {
-		t.Errorf("LastWarning is not the named constant: %q", cd.LastWarning)
+	// v0.254.0 (R-557 release C): the notice is SAVED in the box's language, so the comparison is
+	// against the bundle text for its key rather than against a Go constant. Same claim, measured one
+	// step further out — a reworded sentence still fails, and so does a note written from a different key.
+	if want := m.note(tier2UnitPreservedKey); cd.LastWarning != want &&
+		!strings.Contains(cd.LastWarning, want) {
+		t.Errorf("LastWarning is not the named notice: %q", cd.LastWarning)
 	}
 	// And the coverage the restore surface reads agrees, from the ARTIFACT rather than the record.
 	cov, err := m.Tier2RestoreCoverage("app")