(new): expand runtime APIs

(fix): harden concurrent lifecycle
(tests): add regression coverage
(doc): update v1.2 guidance

bot_opts_loader_test.go

@@ -46,6 +46,21 @@ func TestBotOptsFileJSONCodecRoundTrip(t *testing.T) {
 	}
 }
 
+func TestBotOptsFileRejectsNilInputs(t *testing.T) {
+	if _, err := (BotOptsFileJSONCodec{}).ToBytes(nil); !errors.Is(err, ErrOptsIsNil) {
+		t.Fatalf("ToBytes error = %v, want ErrOptsIsNil", err)
+	}
+	if _, err := LoadBotOptsFile(nil, "unused"); !errors.Is(err, ErrCodecIsNil) {
+		t.Fatalf("LoadBotOptsFile error = %v, want ErrCodecIsNil", err)
+	}
+	if err := SaveBotOptsFile(nil, "unused", &BotOpts{}); !errors.Is(err, ErrCodecIsNil) {
+		t.Fatalf("SaveBotOptsFile error = %v, want ErrCodecIsNil", err)
+	}
+	if err := SaveBotOptsFile(BotOptsFileJSONCodec{}, "unused", nil); !errors.Is(err, ErrOptsIsNil) {
+		t.Fatalf("SaveBotOptsFile nil opts error = %v, want ErrOptsIsNil", err)
+	}
+}
+
 func TestLoadBotOptsFileExpandsEnvPlaceholders(t *testing.T) {
 	t.Setenv("TG_TOKEN", "TOKEN_FROM_ENV")
 	t.Setenv("BOT_API_URL", "https://api.example.invalid")