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/util/msgerr.go

@@ -149,3 +149,25 @@ func ErrText(lang string, err error) string {
 	}
 	return err.Error()
 }
+
+// Text renders a bundle message in a KNOWN language — for a producer that has no request.
+//
+// Release C (v0.254.0) uses it for the sentences a background run SAVES: the note under last night's
+// backup, the last error, the proof result. Those are written at 03:00 and read days later, so there
+// is no reader to ask; the operator ruling (slice 2 §16, option 1) is that they are written in the
+// box's language AT WRITE TIME and shown verbatim afterwards.
+//
+// The consequence, stated rather than hidden: a household that switches language sees last night's
+// note in the old language until the next run rewrites it. The alternative — storing a code and
+// rendering live — needs a dozen new persisted fields and a legacy path for each, which is the
+// R-570 shape a dozen times over.
+func Text(lang, key string, args ...interface{}) string {
+	b, err := i18n.Shared()
+	if err != nil {
+		return key
+	}
+	if len(args) == 0 {
+		return b.Msg(lang, key)
+	}
+	return b.Msgf(lang, key, args...)
+}