wip: add long message helpers and payload type controls

- add centralized message validation errors
- switch command handlers to return error
- add explicit long plain-text reply helpers
- support strict payload type policy with debug logging
- document versioning and changelog workflow

errors.go

@@ -0,0 +1,59 @@
+package laniakea
+
+import (
+	"errors"
+	"fmt"
+	"unicode/utf8"
+)
+
+const (
+	maxMessageTextLen    = 4096
+	maxMessageCaptionLen = 1024
+)
+
+var (
+	// ErrEmptyMessage reports that a required message text is empty.
+	ErrEmptyMessage = errors.New("empty message")
+	// ErrMessageTooLong reports that a message exceeds Telegram's text limit.
+	ErrMessageTooLong = errors.New("message too long")
+	// ErrCaptionTooLong reports that a caption exceeds Telegram's caption limit.
+	ErrCaptionTooLong = errors.New("caption too long")
+	// ErrMessageSplitImpossible reports that automatic message splitting cannot preserve semantics.
+	ErrMessageSplitImpossible = errors.New("message split is impossible")
+	// ErrPayloadTypeMismatch reports that callback payload encoding does not match bot policy.
+	ErrPayloadTypeMismatch = errors.New("payload type mismatch")
+	// ErrDraftChatIDZero reports that a draft has no target chat ID.
+	ErrDraftChatIDZero = errors.New("zero draft chat ID")
+	// ErrMessageContextNil reports that an operation requires ctx.Msg but none is set.
+	ErrMessageContextNil = errors.New("message context is nil")
+	// ErrEditTargetMissing reports that an edit operation has no message target.
+	ErrEditTargetMissing = errors.New("edit target is missing")
+	// ErrCallbackMessageMissing reports that a callback operation has no callback message target.
+	ErrCallbackMessageMissing = errors.New("callback message is missing")
+	// ErrDraftProviderNil reports that draft creation was requested without a draft provider.
+	ErrDraftProviderNil = errors.New("draft provider is nil")
+	// ErrAPIIsNil reports that an operation requires an API client but none is set.
+	ErrAPIIsNil = errors.New("api is nil")
+	// ErrMessageIDZero reports that an operation requires a non-zero message ID.
+	ErrMessageIDZero = errors.New("message ID is zero")
+)
+
+func validateMessageText(text string) error {
+	length := utf8.RuneCountInString(text)
+	switch {
+	case length == 0:
+		return ErrEmptyMessage
+	case length > maxMessageTextLen:
+		return fmt.Errorf("%w: got %d, limit %d", ErrMessageTooLong, length, maxMessageTextLen)
+	default:
+		return nil
+	}
+}
+
+func validateCaptionText(text string) error {
+	length := utf8.RuneCountInString(text)
+	if length > maxMessageCaptionLen {
+		return fmt.Errorf("%w: got %d, limit %d", ErrCaptionTooLong, length, maxMessageCaptionLen)
+	}
+	return nil
+}