fix(2meet-data-optimizer): report entity group name collisions instead of silently dropping

- register_group() keeps the first definition but records a field diff (added/removed/changed) when the same entity/group is re-registered differently; identical re-registration stays silent
- Surface collisions via Site Health (wpdo_entity_group_collisions), the admin Doctor tab, and wp wpdo doctor; warning log throttled to once a day
- Verify: EntityRegistryCollisionTest (7); core unit 613 / integration 432, HP 141/49, WC 10/22 OK
- PR: PR-017

includes/engine/class-tmdo-entity-registry.php

@@ -31,6 +31,9 @@ final class TMDO_Entity_Registry {
 	/** @var array<int, array{type:string, group:string, fields:array}> 待建表的 Schema 清單 */
 	private static array $pending_schemas = array();
 
+	/** @var array<string, array> "entity/group" → 同名群組以不同定義重複註冊的紀錄 */
+	private static array $collisions = array();
+
 	/** 合法的欄位型別 */
 	public const VALID_TYPES = array(
 		'text',
@@ -54,6 +57,7 @@ final class TMDO_Entity_Registry {
 		self::$groups          = array();
 		self::$field_index     = array();
 		self::$pending_schemas = array();
+		self::$collisions      = array();
 	}
 
 	// ─────────────────────────────────────────────────────────
@@ -105,11 +109,6 @@ final class TMDO_Entity_Registry {
 			return false;
 		}
 
-		// 防重複登錄
-		if ( isset( self::$groups[ $entity_type ][ $group_name ] ) ) {
-			return false;
-		}
-
 		// 驗證並正規化欄位定義
 		$normalized = array();
 
@@ -141,15 +140,25 @@ final class TMDO_Entity_Registry {
 			$normalized_field['entity_type'] = $entity_type;
 
 			$normalized[] = $normalized_field;
-
-			// 建立索引以供快速查詢
-			self::$field_index[ $entity_type ][ $normalized_field['key'] ] = $normalized_field;
 		}
 
 		if ( empty( $normalized ) ) {
 			return false;
 		}
 
+		// 防重複登錄：相同定義（init:1 重新觸發）靜默略過；定義不同則記錄衝突，保留先註冊者。
+		if ( isset( self::$groups[ $entity_type ][ $group_name ] ) ) {
+			if ( self::$groups[ $entity_type ][ $group_name ] !== $normalized ) {
+				self::record_collision( $entity_type, $group_name, self::$groups[ $entity_type ][ $group_name ], $normalized );
+			}
+			return false;
+		}
+
+		// 建立索引以供快速查詢
+		foreach ( $normalized as $normalized_field ) {
+			self::$field_index[ $entity_type ][ $normalized_field['key'] ] = $normalized_field;
+		}
+
 		self::$groups[ $entity_type ][ $group_name ] = $normalized;
 
 		// 加入待建表佇列
@@ -162,6 +171,51 @@ final class TMDO_Entity_Registry {
 		return true;
 	}
 
+	/**
+	 * 記錄同名群組衝突（每個 entity/group 每請求一筆），並寫入 warning。
+	 *
+	 * 註冊每個請求都會跑，warning 以 transient 節流為每天一次，避免灌爆 wpdo_errors。
+	 */
+	private static function record_collision( string $entity_type, string $group_name, array $existing, array $incoming ): void {
+		$id = $entity_type . '/' . $group_name;
+		if ( isset( self::$collisions[ $id ] ) ) {
+			return;
+		}
+
+		$old = array_column( $existing, null, 'key' );
+		$new = array_column( $incoming, null, 'key' );
+
+		$changed = array();
+		foreach ( array_intersect_key( $new, $old ) as $key => $field ) {
+			if ( $field !== $old[ $key ] ) {
+				$changed[] = (string) $key;
+			}
+		}
+
+		self::$collisions[ $id ] = array(
+			'entity_type' => $entity_type,
+			'group'       => $group_name,
+			'added'       => array_map( 'strval', array_keys( array_diff_key( $new, $old ) ) ),
+			'removed'     => array_map( 'strval', array_keys( array_diff_key( $old, $new ) ) ),
+			'changed'     => $changed,
+		);
+
+		$throttle = 'tmdo_group_collision_' . md5( (string) wp_json_encode( self::$collisions[ $id ] ) );
+		if ( class_exists( 'TMDO_Logger' ) && false === get_transient( $throttle ) ) {
+			set_transient( $throttle, 1, DAY_IN_SECONDS );
+			TMDO_Logger::warning( 'entity_group_collision', self::$collisions[ $id ] );
+		}
+	}
+
+	/**
+	 * 本請求偵測到的同名群組衝突（第二份定義已被捨棄）。
+	 *
+	 * @return array<int, array{entity_type:string, group:string, added:string[], removed:string[], changed:string[]}>
+	 */
+	public static function get_collisions(): array {
+		return array_values( self::$collisions );
+	}
+
 	// ─────────────────────────────────────────────────────────
 	// 查詢 API
 	// ─────────────────────────────────────────────────────────