feat(M01): add typed domain identities

Work-Package: M01-FND-DOMAIN-IDENTITIES-001

Agent: sindo-main-codex

src/domain/identity/content_id.gd

@@ -0,0 +1,43 @@
+class_name ContentId
+extends RefCounted
+
+## Stable authored-content identity serialized as canonical lowercase UUID text.
+## It is independent of runtime entities, server database entries and wire GUIDs.
+
+var uuid_text: String:
+	get:
+		return _uuid_text
+
+var _uuid_text: String
+
+
+## Normalizes surrounding whitespace and hexadecimal letter case.
+func _init(uuid_text_value: String) -> void:
+	_uuid_text = uuid_text_value.strip_edges().to_lower()
+
+
+## Reports whether the value has the canonical 8-4-4-4-12 UUID text shape.
+func is_valid() -> bool:
+	if _uuid_text.length() != 36:
+		return false
+	for character_index in range(_uuid_text.length()):
+		if character_index in [8, 13, 18, 23]:
+			if _uuid_text[character_index] != "-":
+				return false
+		elif not _is_lowercase_hexadecimal_character(_uuid_text[character_index]):
+			return false
+	return true
+
+
+## Compares stable content identity by normalized UUID text.
+func equals(other_content_id: ContentId) -> bool:
+	return other_content_id != null and _uuid_text == other_content_id.uuid_text
+
+
+## Returns the canonical dictionary/serialization key.
+func to_key() -> String:
+	return _uuid_text
+
+
+func _is_lowercase_hexadecimal_character(character: String) -> bool:
+	return (character >= "0" and character <= "9") or (character >= "a" and character <= "f")