(new): expand runtime APIs

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

errors.go

@@ -38,6 +38,8 @@ var (
 	ErrAPIIsNil = errors.New("api is nil")
 	// ErrMessageIDZero reports that an operation requires a non-zero message ID.
 	ErrMessageIDZero = errors.New("message ID is zero")
+	// ErrCodecIsNil reports that a config operation received a nil codec.
+	ErrCodecIsNil = errors.New("codec is nil")
 )
 var (
 	// ErrBindArgsTargetNotPointer reports that BindArgs received a nil or non-pointer destination.
@@ -66,6 +68,8 @@ var (
 	ErrHandlerExecutorNil = errors.New("handler executor is nil")
 	// ErrHandlerPanic reports a panic recovered from a user handler.
 	ErrHandlerPanic = errors.New("handler panicked")
+	// ErrObserverShutdownTimeout reports that observer callbacks did not stop before shutdown timed out.
+	ErrObserverShutdownTimeout = errors.New("observer shutdown timed out")
 	// ErrInlineKeyboardButtonAction reports a button without exactly one action.
 	ErrInlineKeyboardButtonAction = errors.New("inline keyboard button must have exactly one action")
 	// ErrCallbackDataLength reports callback data outside Telegram's 1-64 byte range.