diff --git a/admin/class-tmdo-admin.php b/admin/class-tmdo-admin.php
index e4fbc65..c3afe3a 100644
--- a/admin/class-tmdo-admin.php
+++ b/admin/class-tmdo-admin.php
@@ -2990,7 +2990,7 @@ wpdo.getListings({ per_page: 3 }).then(r => console.log(r));'
 		?>
 		<h2><?php esc_html_e( '健康檢查（Doctor）', '2meet-data-optimizer' ); ?></h2>
 		<p class="description">
-			<?php esc_html_e( '7 項自我診斷檢查：schema 完整性、錯誤預算、hook 衝突、autoload 大小、postmeta 爆量、orphan zone rows、缺少快照。', '2meet-data-optimizer' ); ?>
+			<?php esc_html_e( '8 項自我診斷檢查：schema 完整性、錯誤預算、hook 衝突、autoload 大小、postmeta 爆量、orphan zone rows、缺少快照、實體群組名稱衝突。', '2meet-data-optimizer' ); ?>
 		</p>
 		<p>
 			<a class="button" href="<?php echo esc_url( admin_url( 'site-health.php' ) ); ?>">
@@ -3004,13 +3004,14 @@ wpdo.getListings({ per_page: 3 }).then(r => console.log(r));'
 		}
 
 		$tests = array(
-			'wpdo_schema_drift'       => array( 'check_schema_drift', __( 'Schema 完整性', '2meet-data-optimizer' ) ),
-			'wpdo_error_budget'       => array( 'check_error_budget', __( '錯誤預算（過去 7 天）', '2meet-data-optimizer' ) ),
-			'wpdo_hook_conflicts'     => array( 'check_hook_conflicts', __( 'Hook 衝突', '2meet-data-optimizer' ) ),
-			'wpdo_autoload_bloat'     => array( 'check_autoload_bloat', __( 'Autoload 大小', '2meet-data-optimizer' ) ),
-			'wpdo_postmeta_explosion' => array( 'check_postmeta_explosion', __( 'wp_postmeta 爆量', '2meet-data-optimizer' ) ),
-			'wpdo_orphan_zone_rows'   => array( 'check_orphan_zone_rows', __( 'Orphan zone rows', '2meet-data-optimizer' ) ),
-			'wpdo_missing_snapshot'   => array( 'check_missing_snapshot', __( '缺少最近快照', '2meet-data-optimizer' ) ),
+			'wpdo_schema_drift'            => array( 'check_schema_drift', __( 'Schema 完整性', '2meet-data-optimizer' ) ),
+			'wpdo_error_budget'            => array( 'check_error_budget', __( '錯誤預算（過去 7 天）', '2meet-data-optimizer' ) ),
+			'wpdo_hook_conflicts'          => array( 'check_hook_conflicts', __( 'Hook 衝突', '2meet-data-optimizer' ) ),
+			'wpdo_autoload_bloat'          => array( 'check_autoload_bloat', __( 'Autoload 大小', '2meet-data-optimizer' ) ),
+			'wpdo_postmeta_explosion'      => array( 'check_postmeta_explosion', __( 'wp_postmeta 爆量', '2meet-data-optimizer' ) ),
+			'wpdo_orphan_zone_rows'        => array( 'check_orphan_zone_rows', __( 'Orphan zone rows', '2meet-data-optimizer' ) ),
+			'wpdo_missing_snapshot'        => array( 'check_missing_snapshot', __( '缺少最近快照', '2meet-data-optimizer' ) ),
+			'wpdo_entity_group_collisions' => array( 'check_entity_group_collisions', __( '實體群組名稱衝突', '2meet-data-optimizer' ) ),
 		);
 		?>
 		<table class="widefat striped">
diff --git a/admin/class-tmdo-help-tabs.php b/admin/class-tmdo-help-tabs.php
index c1c36ba..b4899a4 100644
--- a/admin/class-tmdo-help-tabs.php
+++ b/admin/class-tmdo-help-tabs.php
@@ -184,7 +184,7 @@ class TMDO_Help_Tabs {
 	 * @return string
 	 */
 	private static function content_doctor(): string {
-		return '<p>' . esc_html__( '7 項自動健康檢查：', '2meet-data-optimizer' ) . '</p>'
+		return '<p>' . esc_html__( '8 項自動健康檢查：', '2meet-data-optimizer' ) . '</p>'
 			. '<ol class="wpdo-list-disc">'
 			. '<li><strong>schema_drift</strong> — ' . esc_html__( '所有 v2 表是否存在', '2meet-data-optimizer' ) . '</li>'
 			. '<li><strong>error_budget</strong> — ' . esc_html__( '7 天內 wp_wpdo_errors 行數', '2meet-data-optimizer' ) . '</li>'
@@ -193,6 +193,7 @@ class TMDO_Help_Tabs {
 			. '<li><strong>postmeta_explosion</strong> — ' . esc_html__( 'wp_postmeta > 5M 行', '2meet-data-optimizer' ) . '</li>'
 			. '<li><strong>orphan_zone_rows</strong> — ' . esc_html__( '已 idle 的 module 但 zone 表還有資料', '2meet-data-optimizer' ) . '</li>'
 			. '<li><strong>missing_snapshot</strong> — ' . esc_html__( '在 cutover/cleanup/complete 但 7 天沒 snapshot', '2meet-data-optimizer' ) . '</li>'
+			. '<li><strong>entity_group_collisions</strong> — ' . esc_html__( '同名實體群組被不同外掛以不同欄位註冊（後者被忽略）', '2meet-data-optimizer' ) . '</li>'
 			. '</ol>'
 			. '<p>' . esc_html__( '結果有 5 分鐘 transient cache，剛操作完想立刻看新值請等下個週期。', '2meet-data-optimizer' ) . '</p>';
 	}
diff --git a/cli/class-tmdo-cli.php b/cli/class-tmdo-cli.php
index e227736..5c0023c 100644
--- a/cli/class-tmdo-cli.php
+++ b/cli/class-tmdo-cli.php
@@ -330,6 +330,25 @@ class TMDO_CLI {
 			WP_CLI::log( '  [OK] Crypto key derivable (AUTH_KEY / SECURE_AUTH_SALT present)' );
 		}
 
+		// ── Entity group name collisions ─────────────────────────────────────────
+		$collisions = TMDO_Entity_Registry::get_collisions();
+		if ( empty( $collisions ) ) {
+			WP_CLI::log( '  [OK] No entity group name collisions' );
+		}
+		foreach ( $collisions as $c ) {
+			WP_CLI::warning(
+				sprintf(
+					'  [COLLISION] %s/%s registered twice with different fields (second ignored) — added: %s; removed: %s; changed: %s',
+					$c['entity_type'],
+					$c['group'],
+					implode( ', ', $c['added'] ) ?: '-',
+					implode( ', ', $c['removed'] ) ?: '-',
+					implode( ', ', $c['changed'] ) ?: '-'
+				)
+			);
+			$all_ok = false;
+		}
+
 		// Check recent errors.
 		$errors = TMDO_Logger::get_recent( '', 5 );
 		if ( ! empty( $errors ) ) {
diff --git a/includes/diagnostic/class-tmdo-site-health.php b/includes/diagnostic/class-tmdo-site-health.php
index 77db2d9..bba38c2 100644
--- a/includes/diagnostic/class-tmdo-site-health.php
+++ b/includes/diagnostic/class-tmdo-site-health.php
@@ -2,7 +2,7 @@
 /**
  * TMDO_Site_Health — WordPress Site Health integration (v2.2.0 M3).
  *
- * Registers 7 tests under Tools → Site Health → Status:
+ * Registers 8 tests under Tools → Site Health → Status:
  *   1. wpdo_schema_drift          (critical)
  *   2. wpdo_error_budget          (recommended)
  *   3. wpdo_hook_conflicts        (recommended)
@@ -10,6 +10,7 @@
  *   5. wpdo_postmeta_explosion    (recommended)
  *   6. wpdo_orphan_zone_rows      (recommended)
  *   7. wpdo_missing_snapshot      (critical)
+ *   8. wpdo_entity_group_collisions (recommended)
  *
  * Each test result is cached for 5 minutes to keep Site Health responsive.
  *
@@ -34,13 +35,14 @@ class TMDO_Site_Health {
 
 	/** Test name → callable suffix mapping. */
 	private const TESTS = array(
-		'wpdo_schema_drift'       => 'check_schema_drift',
-		'wpdo_error_budget'       => 'check_error_budget',
-		'wpdo_hook_conflicts'     => 'check_hook_conflicts',
-		'wpdo_autoload_bloat'     => 'check_autoload_bloat',
-		'wpdo_postmeta_explosion' => 'check_postmeta_explosion',
-		'wpdo_orphan_zone_rows'   => 'check_orphan_zone_rows',
-		'wpdo_missing_snapshot'   => 'check_missing_snapshot',
+		'wpdo_schema_drift'            => 'check_schema_drift',
+		'wpdo_error_budget'            => 'check_error_budget',
+		'wpdo_hook_conflicts'          => 'check_hook_conflicts',
+		'wpdo_autoload_bloat'          => 'check_autoload_bloat',
+		'wpdo_postmeta_explosion'      => 'check_postmeta_explosion',
+		'wpdo_orphan_zone_rows'        => 'check_orphan_zone_rows',
+		'wpdo_missing_snapshot'        => 'check_missing_snapshot',
+		'wpdo_entity_group_collisions' => 'check_entity_group_collisions',
 	);
 
 	/**
@@ -53,7 +55,7 @@ class TMDO_Site_Health {
 	}
 
 	/**
-	 * Register the 7 tests with WP Site Health.
+	 * Register the 8 tests with WP Site Health.
 	 *
 	 * @param array $tests Existing tests.
 	 * @return array
@@ -76,13 +78,14 @@ class TMDO_Site_Health {
 	 */
 	private static function label_for( string $key ): string {
 		$map = array(
-			'wpdo_schema_drift'       => __( 'WPDO schema drift', '2meet-data-optimizer' ),
-			'wpdo_error_budget'       => __( 'WPDO error budget', '2meet-data-optimizer' ),
-			'wpdo_hook_conflicts'     => __( 'WPDO hook conflicts', '2meet-data-optimizer' ),
-			'wpdo_autoload_bloat'     => __( 'WPDO autoload bloat', '2meet-data-optimizer' ),
-			'wpdo_postmeta_explosion' => __( 'WPDO postmeta explosion', '2meet-data-optimizer' ),
-			'wpdo_orphan_zone_rows'   => __( 'WPDO orphan zone rows', '2meet-data-optimizer' ),
-			'wpdo_missing_snapshot'   => __( 'WPDO missing snapshot', '2meet-data-optimizer' ),
+			'wpdo_schema_drift'            => __( 'WPDO schema drift', '2meet-data-optimizer' ),
+			'wpdo_error_budget'            => __( 'WPDO error budget', '2meet-data-optimizer' ),
+			'wpdo_hook_conflicts'          => __( 'WPDO hook conflicts', '2meet-data-optimizer' ),
+			'wpdo_autoload_bloat'          => __( 'WPDO autoload bloat', '2meet-data-optimizer' ),
+			'wpdo_postmeta_explosion'      => __( 'WPDO postmeta explosion', '2meet-data-optimizer' ),
+			'wpdo_orphan_zone_rows'        => __( 'WPDO orphan zone rows', '2meet-data-optimizer' ),
+			'wpdo_missing_snapshot'        => __( 'WPDO missing snapshot', '2meet-data-optimizer' ),
+			'wpdo_entity_group_collisions' => __( 'WPDO entity group collisions', '2meet-data-optimizer' ),
 		);
 		return $map[ $key ] ?? $key;
 	}
@@ -425,6 +428,46 @@ class TMDO_Site_Health {
 
 	// ─── helpers ──────────────────────────────────────────────────────────
 
+	// ─── Test 8: Entity group name collisions ───────────────────────────
+
+	/**
+	 * Report entity groups registered twice with different definitions.
+	 *
+	 * Not cached: the collision list is in-memory state rebuilt on every
+	 * request, so reading it is free and a transient would only go stale.
+	 *
+	 * @return array Site Health result.
+	 */
+	public static function check_entity_group_collisions(): array {
+		$collisions = class_exists( 'TMDO_Entity_Registry' ) ? TMDO_Entity_Registry::get_collisions() : array();
+		if ( empty( $collisions ) ) {
+			return self::wrap( 'wpdo_entity_group_collisions', self::pass( __( 'No entity group name collisions.', '2meet-data-optimizer' ) ) );
+		}
+		$lines = array();
+		foreach ( $collisions as $c ) {
+			$lines[] = sprintf(
+				'%s/%s (+%s −%s ~%s)',
+				$c['entity_type'],
+				$c['group'],
+				implode( ',', $c['added'] ) ?: '-',
+				implode( ',', $c['removed'] ) ?: '-',
+				implode( ',', $c['changed'] ) ?: '-'
+			);
+		}
+		return self::wrap(
+			'wpdo_entity_group_collisions',
+			self::fail(
+				__( 'WPDO entity group name collisions', '2meet-data-optimizer' ),
+				sprintf(
+					/* translators: %s: list of entity/group names with field differences */
+					__( 'Another plugin registered these groups with a different field list; its definition was ignored and the first one kept: %s', '2meet-data-optimizer' ),
+					implode( '; ', $lines )
+				),
+				'recommended'
+			)
+		);
+	}
+
 	/**
 	 * Wrap a raw check result with required Site Health envelope fields.
 	 *
diff --git a/includes/engine/class-tmdo-entity-registry.php b/includes/engine/class-tmdo-entity-registry.php
index c4e0a5a..c6e6ec1 100644
--- a/includes/engine/class-tmdo-entity-registry.php
+++ b/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
 	// ─────────────────────────────────────────────────────────
diff --git a/tests/unit/EntityRegistryCollisionTest.php b/tests/unit/EntityRegistryCollisionTest.php
new file mode 100644
index 0000000..1b21b49
--- /dev/null
+++ b/tests/unit/EntityRegistryCollisionTest.php
@@ -0,0 +1,97 @@
+<?php
+declare(strict_types=1);
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Entity group name collisions.
+ *
+ * Two providers registering the same entity/group name used to have the
+ * second definition dropped with no trace. Identical re-registration (core
+ * re-fires the registration hooks on init:1) stays silent; a different
+ * definition is recorded with a field diff and surfaced in Site Health.
+ */
+class EntityRegistryCollisionTest extends TestCase {
+
+	protected function setUp(): void {
+		if ( ! class_exists( 'TMDO_Site_Health' ) ) {
+			require_once TMDO_PATH . 'includes/diagnostic/class-tmdo-site-health.php';
+		}
+		TMDO_Entity_Registry::init();
+		TMDO_Entity_Registry::register_adapter( 'post', $this->createMock( TMDO_Entity_Adapter_Interface::class ) );
+		$GLOBALS['_wp_options'] = array();
+	}
+
+	private function first_definition(): array {
+		return array(
+			array( 'key' => 'hp_price', 'type' => 'decimal', 'searchable' => true ),
+			array( 'key' => 'hp_featured', 'type' => 'boolean' ),
+		);
+	}
+
+	public function test_identical_reregistration_is_silent(): void {
+		$this->assertTrue( TMDO_Entity_Registry::register_group( 'post', 'hp_listing_core', $this->first_definition() ) );
+		$this->assertFalse( TMDO_Entity_Registry::register_group( 'post', 'hp_listing_core', $this->first_definition() ) );
+
+		$this->assertSame( array(), TMDO_Entity_Registry::get_collisions() );
+	}
+
+	public function test_different_definition_is_recorded_with_field_diff(): void {
+		TMDO_Entity_Registry::register_group( 'post', 'hp_listing_core', $this->first_definition() );
+
+		$second = array(
+			array( 'key' => 'hp_price', 'type' => 'integer', 'searchable' => true ),
+			array( 'key' => 'hp_vendor', 'type' => 'integer' ),
+		);
+		$this->assertFalse( TMDO_Entity_Registry::register_group( 'post', 'hp_listing_core', $second ) );
+
+		$collisions = TMDO_Entity_Registry::get_collisions();
+		$this->assertCount( 1, $collisions );
+		$this->assertSame( 'post', $collisions[0]['entity_type'] );
+		$this->assertSame( 'hp_listing_core', $collisions[0]['group'] );
+		$this->assertSame( array( 'hp_vendor' ), $collisions[0]['added'] );
+		$this->assertSame( array( 'hp_featured' ), $collisions[0]['removed'] );
+		$this->assertSame( array( 'hp_price' ), $collisions[0]['changed'] );
+	}
+
+	public function test_first_definition_wins(): void {
+		TMDO_Entity_Registry::register_group( 'post', 'hp_listing_core', $this->first_definition() );
+		TMDO_Entity_Registry::register_group( 'post', 'hp_listing_core', array( array( 'key' => 'hp_vendor', 'type' => 'integer' ) ) );
+
+		$this->assertSame( array( 'hp_price', 'hp_featured' ), TMDO_Entity_Registry::get_group_keys( 'post', 'hp_listing_core' ) );
+		$this->assertNull( TMDO_Entity_Registry::get_field( 'post', 'hp_vendor' ) );
+	}
+
+	public function test_same_collision_is_recorded_once_per_request(): void {
+		TMDO_Entity_Registry::register_group( 'post', 'g', $this->first_definition() );
+		$other = array( array( 'key' => 'x', 'type' => 'text' ) );
+		TMDO_Entity_Registry::register_group( 'post', 'g', $other );
+		TMDO_Entity_Registry::register_group( 'post', 'g', $other );
+
+		$this->assertCount( 1, TMDO_Entity_Registry::get_collisions() );
+	}
+
+	public function test_init_clears_collisions(): void {
+		TMDO_Entity_Registry::register_group( 'post', 'g', $this->first_definition() );
+		TMDO_Entity_Registry::register_group( 'post', 'g', array( array( 'key' => 'x', 'type' => 'text' ) ) );
+		TMDO_Entity_Registry::init();
+
+		$this->assertSame( array(), TMDO_Entity_Registry::get_collisions() );
+	}
+
+	public function test_site_health_reports_collisions(): void {
+		$this->assertSame( 'good', TMDO_Site_Health::check_entity_group_collisions()['status'] );
+
+		TMDO_Entity_Registry::register_group( 'post', 'hp_listing_core', $this->first_definition() );
+		TMDO_Entity_Registry::register_group( 'post', 'hp_listing_core', array( array( 'key' => 'x', 'type' => 'text' ) ) );
+
+		$result = TMDO_Site_Health::check_entity_group_collisions();
+		$this->assertSame( 'recommended', $result['status'] );
+		$this->assertStringContainsString( 'post/hp_listing_core', $result['description'] );
+	}
+
+	public function test_site_health_registers_the_collision_test(): void {
+		$tests = TMDO_Site_Health::register_tests( array() );
+		$this->assertArrayHasKey( 'wpdo_entity_group_collisions', $tests['direct'] );
+	}
+}