feat: sync langpack and auth updates

Sync telesrv commits 49f9bab and 04d9563 into the public mirror. Exclude private docs and runtime key material per sync rules.

internal/app/langpack/cache_test.go

@@ -0,0 +1,35 @@
+package langpack
+
+import (
+	"testing"
+
+	"telesrv/internal/domain"
+)
+
+func TestLangPackCachesRejectLoadsAcrossFlush(t *testing.T) {
+	packCache := newLangPackCache(1<<20, 8)
+	key := langPackCacheKey{pack: "tdesktop", code: "en", kind: langPackCacheRaw}
+	packEpoch := packCache.loadEpoch()
+	packCache.flush()
+	if packCache.putIfEpoch(key, domain.LangPack{
+		LangPack: "tdesktop",
+		LangCode: "en",
+		Version:  1,
+		Strings:  []domain.LangPackString{{Key: "key", Value: "stale"}},
+	}, packEpoch) {
+		t.Fatal("pre-flush pack load was accepted")
+	}
+	if _, ok := packCache.get(key); ok {
+		t.Fatal("pre-flush pack load became visible")
+	}
+
+	languageCache := newLanguageListCache(8)
+	languageEpoch := languageCache.loadEpoch()
+	languageCache.flush()
+	if languageCache.putIfEpoch("tdesktop", []domain.LangPackLanguage{{LangCode: "en"}}, languageEpoch) {
+		t.Fatal("pre-flush language-list load was accepted")
+	}
+	if _, ok := languageCache.get("tdesktop"); ok {
+		t.Fatal("pre-flush language-list load became visible")
+	}
+}