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

split.go

@@ -0,0 +1,44 @@
+package laniakea
+
+// SplitMessageText splits plain text into Telegram-safe message chunks.
+//
+// The function preserves the original text exactly: concatenating all returned
+// chunks reconstructs text byte-for-byte. It prefers splitting at newlines or
+// spaces within the Telegram message limit and falls back to hard rune-based
+// splits when no separator is available.
+func SplitMessageText(text string) []string {
+	return splitTextByLimit(text, maxMessageTextLen)
+}
+
+func splitTextByLimit(text string, limit int) []string {
+	if text == "" {
+		return nil
+	}
+
+	runes := []rune(text)
+	chunks := make([]string, 0, len(runes)/limit+1)
+
+	for start := 0; start < len(runes); {
+		end := start + limit
+		if end >= len(runes) {
+			chunks = append(chunks, string(runes[start:]))
+			break
+		}
+
+		splitAt := -1
+		for i := end - 1; i > start; i-- {
+			if runes[i] == '\n' || runes[i] == ' ' {
+				splitAt = i + 1
+				break
+			}
+		}
+		if splitAt == -1 {
+			splitAt = end
+		}
+
+		chunks = append(chunks, string(runes[start:splitAt]))
+		start = splitAt
+	}
+
+	return chunks
+}