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/r553_offsite_quota_test.go

@@ -48,12 +48,12 @@ func TestR553_OffsiteQuota_DecisionSurvivesWordingChange(t *testing.T) {
 func TestR553_OffsiteQuota_HeadLineSurvivesWordingChange(t *testing.T) {
 	tgt := &settings.OffboxTarget{Host: "nas.local", User: "felhom", RepoPath: "/srv/repo"}
 	translated := util.KindErrorf(ErrOffsiteQuota, "The remote backup is over its storage quota (51/50 GB).")
-	msg := offsiteFailureMessage(tgt, translated, 12*time.Second)
+	msg := offsiteFailureMessage(tgt, translated, 12*time.Second, "hu")
 	if !strings.HasPrefix(msg, "A távoli mentés nem fért el a tárhelykereten belül") {
 		t.Errorf("a translated quota failure is reported with the wrong cause line: %q", msg)
 	}
 	unknown := errors.New("The remote backup is over its storage quota (51/50 GB).")
-	if m := offsiteFailureMessage(tgt, unknown, time.Second); strings.HasPrefix(m, "A távoli mentés nem fért el") {
+	if m := offsiteFailureMessage(tgt, unknown, time.Second, "hu"); strings.HasPrefix(m, "A távoli mentés nem fért el") {
 		t.Errorf("an error WITHOUT the kind must not be guessed into the quota class from its words: %q", m)
 	}
 }