diff --git a/backend/internal/repository/auth_identity_legacy_migration_integration_test.go b/backend/internal/repository/auth_identity_legacy_migration_integration_test.go
index 6a6312d4..7f2f363f 100644
--- a/backend/internal/repository/auth_identity_legacy_migration_integration_test.go
+++ b/backend/internal/repository/auth_identity_legacy_migration_integration_test.go
@@ -200,6 +200,252 @@ FROM auth_identity_migration_reports
 	var afterCount int
 	require.NoError(t, tx.QueryRowContext(ctx, `
 SELECT COUNT(*)
+FROM auth_identity_migration_reports
+	`).Scan(&afterCount))
+	require.Equal(t, beforeCount, afterCount)
+}
+
+func TestAuthIdentityLegacyExternalSafetyMigration_ReportsConflictsAndDowngradesInvalidJSON(t *testing.T) {
+	tx := testTx(t)
+	ctx := context.Background()
+
+	migrationPath := filepath.Join("..", "..", "migrations", "116_auth_identity_legacy_external_safety_reports.sql")
+	migrationSQL, err := os.ReadFile(migrationPath)
+	require.NoError(t, err)
+
+	_, err = tx.ExecContext(ctx, `
+CREATE TABLE IF NOT EXISTS user_external_identities (
+	id BIGSERIAL PRIMARY KEY,
+	user_id BIGINT NOT NULL,
+	provider TEXT NOT NULL,
+	provider_user_id TEXT NOT NULL,
+	provider_union_id TEXT NULL,
+	provider_username TEXT NOT NULL DEFAULT '',
+	display_name TEXT NOT NULL DEFAULT '',
+	profile_url TEXT NOT NULL DEFAULT '',
+	avatar_url TEXT NOT NULL DEFAULT '',
+	metadata TEXT NOT NULL DEFAULT '{}',
+	created_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
+	updated_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+	TRUNCATE TABLE
+		auth_identity_channels,
+		auth_identities,
+		auth_identity_migration_reports,
+		user_external_identities,
+		users
+	RESTART IDENTITY;
+`)
+	require.NoError(t, err)
+
+	userIDs := make([]int64, 0, 8)
+	for _, email := range []string{
+		"linuxdo-conflict-legacy@example.com",
+		"linuxdo-conflict-owner@example.com",
+		"wechat-conflict-legacy@example.com",
+		"wechat-conflict-owner@example.com",
+		"wechat-channel-legacy@example.com",
+		"wechat-channel-owner@example.com",
+		"linuxdo-invalid-json@example.com",
+		"wechat-openid-invalid-json@example.com",
+	} {
+		var userID int64
+		require.NoError(t, tx.QueryRowContext(ctx, `
+INSERT INTO users (email, password_hash, role, status, balance, concurrency)
+VALUES ($1, 'hash', 'user', 'active', 0, 1)
+RETURNING id`, email).Scan(&userID))
+		userIDs = append(userIDs, userID)
+	}
+
+	linuxdoConflictLegacyUserID := userIDs[0]
+	linuxdoConflictOwnerUserID := userIDs[1]
+	wechatConflictLegacyUserID := userIDs[2]
+	wechatConflictOwnerUserID := userIDs[3]
+	wechatChannelLegacyUserID := userIDs[4]
+	wechatChannelOwnerUserID := userIDs[5]
+	linuxdoInvalidJSONUserID := userIDs[6]
+	wechatInvalidOpenIDUserID := userIDs[7]
+
+	require.NoError(t, tx.QueryRowContext(ctx, `
+INSERT INTO auth_identities (user_id, provider_type, provider_key, provider_subject, metadata)
+VALUES ($1, 'linuxdo', 'linuxdo', 'linuxdo-conflict', '{}'::jsonb)
+RETURNING id`, linuxdoConflictOwnerUserID).Scan(new(int64)))
+
+	require.NoError(t, tx.QueryRowContext(ctx, `
+INSERT INTO auth_identities (user_id, provider_type, provider_key, provider_subject, metadata)
+VALUES ($1, 'wechat', 'wechat-main', 'union-conflict', '{}'::jsonb)
+RETURNING id`, wechatConflictOwnerUserID).Scan(new(int64)))
+
+	var wechatChannelOwnerIdentityID int64
+	require.NoError(t, tx.QueryRowContext(ctx, `
+INSERT INTO auth_identities (user_id, provider_type, provider_key, provider_subject, metadata)
+VALUES ($1, 'wechat', 'wechat-main', 'union-channel-owner', '{}'::jsonb)
+RETURNING id`, wechatChannelOwnerUserID).Scan(&wechatChannelOwnerIdentityID))
+
+	require.NoError(t, tx.QueryRowContext(ctx, `
+INSERT INTO auth_identity_channels (
+	identity_id,
+	provider_type,
+	provider_key,
+	channel,
+	channel_app_id,
+	channel_subject,
+	metadata
+)
+VALUES ($1, 'wechat', 'wechat-main', 'oa', 'wx-app-conflict', 'openid-channel-conflict', '{}'::jsonb)
+RETURNING id`, wechatChannelOwnerIdentityID).Scan(new(int64)))
+
+	var linuxdoConflictLegacyID int64
+	require.NoError(t, tx.QueryRowContext(ctx, `
+INSERT INTO user_external_identities (
+	user_id,
+	provider,
+	provider_user_id,
+	provider_union_id,
+	provider_username,
+	display_name,
+	metadata
+) VALUES ($1, 'linuxdo', 'linuxdo-conflict', NULL, 'legacy-linuxdo', 'Legacy LinuxDo Conflict', '{"source":"legacy"}')
+RETURNING id
+`, linuxdoConflictLegacyUserID).Scan(&linuxdoConflictLegacyID))
+
+	var wechatConflictLegacyID int64
+	require.NoError(t, tx.QueryRowContext(ctx, `
+INSERT INTO user_external_identities (
+	user_id,
+	provider,
+	provider_user_id,
+	provider_union_id,
+	provider_username,
+	display_name,
+	metadata
+) VALUES ($1, 'wechat', 'openid-union-conflict', 'union-conflict', 'legacy-wechat', 'Legacy WeChat Conflict', '{"channel":"oa","appid":"wx-app-conflict-canon"}')
+RETURNING id
+`, wechatConflictLegacyUserID).Scan(&wechatConflictLegacyID))
+
+	var wechatChannelConflictLegacyID int64
+	require.NoError(t, tx.QueryRowContext(ctx, `
+INSERT INTO user_external_identities (
+	user_id,
+	provider,
+	provider_user_id,
+	provider_union_id,
+	provider_username,
+	display_name,
+	metadata
+) VALUES ($1, 'wechat', 'openid-channel-conflict', 'union-channel-legacy', 'legacy-wechat-channel', 'Legacy WeChat Channel Conflict', '{"channel":"oa","appid":"wx-app-conflict"}')
+RETURNING id
+`, wechatChannelLegacyUserID).Scan(&wechatChannelConflictLegacyID))
+
+	var linuxdoInvalidJSONLegacyID int64
+	require.NoError(t, tx.QueryRowContext(ctx, `
+INSERT INTO user_external_identities (
+	user_id,
+	provider,
+	provider_user_id,
+	provider_union_id,
+	provider_username,
+	display_name,
+	metadata
+) VALUES ($1, 'linuxdo', 'linuxdo-invalid-json', NULL, 'legacy-linuxdo-invalid', 'Legacy LinuxDo Invalid JSON', '{invalid')
+RETURNING id
+`, linuxdoInvalidJSONUserID).Scan(&linuxdoInvalidJSONLegacyID))
+
+	var wechatInvalidOpenIDLegacyID int64
+	require.NoError(t, tx.QueryRowContext(ctx, `
+INSERT INTO user_external_identities (
+	user_id,
+	provider,
+	provider_user_id,
+	provider_union_id,
+	provider_username,
+	display_name,
+	metadata
+) VALUES ($1, 'wechat', 'openid-invalid-json-only', NULL, 'legacy-wechat-invalid', 'Legacy WeChat Invalid JSON', '{still-invalid')
+RETURNING id
+`, wechatInvalidOpenIDUserID).Scan(&wechatInvalidOpenIDLegacyID))
+
+	_, err = tx.ExecContext(ctx, string(migrationSQL))
+	require.NoError(t, err)
+
+	var linuxdoConflictReportCount int
+	require.NoError(t, tx.QueryRowContext(ctx, `
+SELECT COUNT(*)
+FROM auth_identity_migration_reports
+WHERE report_type = 'legacy_external_identity_conflict'
+  AND report_key = $1
+`, "legacy_external_identity:"+strconv.FormatInt(linuxdoConflictLegacyID, 10)).Scan(&linuxdoConflictReportCount))
+	require.Equal(t, 1, linuxdoConflictReportCount)
+
+	var wechatConflictReportCount int
+	require.NoError(t, tx.QueryRowContext(ctx, `
+SELECT COUNT(*)
+FROM auth_identity_migration_reports
+WHERE report_type = 'legacy_external_identity_conflict'
+  AND report_key = $1
+`, "legacy_external_identity:"+strconv.FormatInt(wechatConflictLegacyID, 10)).Scan(&wechatConflictReportCount))
+	require.Equal(t, 1, wechatConflictReportCount)
+
+	var channelConflictReportCount int
+	require.NoError(t, tx.QueryRowContext(ctx, `
+SELECT COUNT(*)
+FROM auth_identity_migration_reports
+WHERE report_type = 'legacy_external_channel_conflict'
+  AND report_key = $1
+`, "legacy_external_identity:"+strconv.FormatInt(wechatChannelConflictLegacyID, 10)).Scan(&channelConflictReportCount))
+	require.Equal(t, 1, channelConflictReportCount)
+
+	var invalidJSONReportCount int
+	require.NoError(t, tx.QueryRowContext(ctx, `
+SELECT COUNT(*)
+FROM auth_identity_migration_reports
+WHERE report_type = 'legacy_external_identity_invalid_metadata_json'
+  AND report_key IN ($1, $2)
+`, "legacy_external_identity:"+strconv.FormatInt(linuxdoInvalidJSONLegacyID, 10), "legacy_external_identity:"+strconv.FormatInt(wechatInvalidOpenIDLegacyID, 10)).Scan(&invalidJSONReportCount))
+	require.Equal(t, 2, invalidJSONReportCount)
+
+	var linuxdoInvalidIdentityCount int
+	require.NoError(t, tx.QueryRowContext(ctx, `
+SELECT COUNT(*)
+FROM auth_identities
+WHERE user_id = $1
+  AND provider_type = 'linuxdo'
+  AND provider_key = 'linuxdo'
+  AND provider_subject = 'linuxdo-invalid-json'
+`, linuxdoInvalidJSONUserID).Scan(&linuxdoInvalidIdentityCount))
+	require.Equal(t, 1, linuxdoInvalidIdentityCount)
+
+	var wechatOpenIDOnlyReportCount int
+	require.NoError(t, tx.QueryRowContext(ctx, `
+SELECT COUNT(*)
+FROM auth_identity_migration_reports
+WHERE report_type = 'wechat_openid_only_requires_remediation'
+  AND report_key = $1
+`, "legacy_external_identity:"+strconv.FormatInt(wechatInvalidOpenIDLegacyID, 10)).Scan(&wechatOpenIDOnlyReportCount))
+	require.Equal(t, 1, wechatOpenIDOnlyReportCount)
+}
+
+func TestAuthIdentityLegacyExternalSafetyMigration_IsSafeWhenLegacyTableMissing(t *testing.T) {
+	tx := testTx(t)
+	ctx := context.Background()
+
+	migrationPath := filepath.Join("..", "..", "migrations", "116_auth_identity_legacy_external_safety_reports.sql")
+	migrationSQL, err := os.ReadFile(migrationPath)
+	require.NoError(t, err)
+
+	var beforeCount int
+	require.NoError(t, tx.QueryRowContext(ctx, `
+SELECT COUNT(*)
+FROM auth_identity_migration_reports
+`).Scan(&beforeCount))
+
+	_, err = tx.ExecContext(ctx, string(migrationSQL))
+	require.NoError(t, err)
+
+	var afterCount int
+	require.NoError(t, tx.QueryRowContext(ctx, `
+SELECT COUNT(*)
 FROM auth_identity_migration_reports
 `).Scan(&afterCount))
 	require.Equal(t, beforeCount, afterCount)
diff --git a/backend/migrations/116_auth_identity_legacy_external_safety_reports.sql b/backend/migrations/116_auth_identity_legacy_external_safety_reports.sql
new file mode 100644
index 00000000..994f3f37
--- /dev/null
+++ b/backend/migrations/116_auth_identity_legacy_external_safety_reports.sql
@@ -0,0 +1,336 @@
+CREATE OR REPLACE FUNCTION public.__migration_116_safe_legacy_metadata_jsonb(input_text TEXT)
+RETURNS JSONB
+LANGUAGE plpgsql
+AS $$
+DECLARE
+    parsed JSONB;
+BEGIN
+    IF input_text IS NULL OR BTRIM(input_text) = '' THEN
+        RETURN '{}'::jsonb;
+    END IF;
+
+    BEGIN
+        parsed := input_text::jsonb;
+    EXCEPTION
+        WHEN OTHERS THEN
+            RETURN '{}'::jsonb;
+    END;
+
+    IF jsonb_typeof(parsed) = 'object' THEN
+        RETURN parsed;
+    END IF;
+
+    RETURN jsonb_build_object('_legacy_metadata_raw_json', parsed);
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION public.__migration_116_is_valid_legacy_metadata_jsonb(input_text TEXT)
+RETURNS BOOLEAN
+LANGUAGE plpgsql
+AS $$
+DECLARE
+    parsed JSONB;
+BEGIN
+    IF input_text IS NULL OR BTRIM(input_text) = '' THEN
+        RETURN TRUE;
+    END IF;
+
+    parsed := input_text::jsonb;
+    RETURN TRUE;
+EXCEPTION
+    WHEN OTHERS THEN
+        RETURN FALSE;
+END;
+$$;
+
+DO $$
+BEGIN
+    IF to_regclass('public.user_external_identities') IS NULL THEN
+        RETURN;
+    END IF;
+
+    EXECUTE $sql$
+INSERT INTO auth_identity_migration_reports (report_type, report_key, details)
+SELECT
+    'legacy_external_identity_invalid_metadata_json',
+    'legacy_external_identity:' || uei.id::text,
+    jsonb_build_object(
+        'legacy_identity_id', uei.id,
+        'user_id', uei.user_id,
+        'provider', LOWER(BTRIM(COALESCE(uei.provider, ''))),
+        'provider_user_id', BTRIM(COALESCE(uei.provider_user_id, '')),
+        'provider_union_id', BTRIM(COALESCE(uei.provider_union_id, '')),
+        'reason', 'legacy metadata is not valid JSON; migration downgraded metadata to empty object',
+        'raw_metadata', LEFT(BTRIM(COALESCE(uei.metadata, '')), 1000),
+        'migration', '116_auth_identity_legacy_external_safety_reports'
+    )
+FROM user_external_identities AS uei
+JOIN users AS u ON u.id = uei.user_id
+WHERE u.deleted_at IS NULL
+  AND BTRIM(COALESCE(uei.metadata, '')) <> ''
+  AND NOT public.__migration_116_is_valid_legacy_metadata_jsonb(uei.metadata)
+ON CONFLICT (report_type, report_key) DO NOTHING;
+$sql$;
+
+    EXECUTE $sql$
+INSERT INTO auth_identity_migration_reports (report_type, report_key, details)
+SELECT
+    'legacy_external_identity_conflict',
+    'legacy_external_identity:' || legacy.id::text,
+    legacy.metadata_json || jsonb_build_object(
+        'legacy_identity_id', legacy.id,
+        'legacy_user_id', legacy.user_id,
+        'existing_identity_id', ai.id,
+        'existing_user_id', ai.user_id,
+        'provider_type', legacy.provider_type,
+        'provider_key', legacy.provider_key,
+        'provider_subject', legacy.provider_subject,
+        'reason', 'legacy canonical identity subject already belongs to another user',
+        'migration', '116_auth_identity_legacy_external_safety_reports'
+    )
+FROM (
+    SELECT
+        uei.id,
+        uei.user_id,
+        LOWER(BTRIM(COALESCE(uei.provider, ''))) AS provider_type,
+        CASE
+            WHEN LOWER(BTRIM(COALESCE(uei.provider, ''))) = 'wechat' THEN 'wechat-main'
+            ELSE 'linuxdo'
+        END AS provider_key,
+        CASE
+            WHEN LOWER(BTRIM(COALESCE(uei.provider, ''))) = 'wechat' THEN BTRIM(COALESCE(uei.provider_union_id, ''))
+            ELSE BTRIM(COALESCE(uei.provider_user_id, ''))
+        END AS provider_subject,
+        BTRIM(COALESCE(uei.provider_user_id, '')) AS provider_user_id,
+        BTRIM(COALESCE(uei.provider_union_id, '')) AS provider_union_id,
+        BTRIM(COALESCE(uei.provider_username, '')) AS provider_username,
+        BTRIM(COALESCE(uei.display_name, '')) AS display_name,
+        public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) AS metadata_json
+    FROM user_external_identities AS uei
+    JOIN users AS u ON u.id = uei.user_id
+    WHERE u.deleted_at IS NULL
+      AND LOWER(BTRIM(COALESCE(uei.provider, ''))) IN ('linuxdo', 'wechat')
+      AND (
+          (LOWER(BTRIM(COALESCE(uei.provider, ''))) = 'linuxdo' AND BTRIM(COALESCE(uei.provider_user_id, '')) <> '')
+          OR
+          (LOWER(BTRIM(COALESCE(uei.provider, ''))) = 'wechat' AND BTRIM(COALESCE(uei.provider_union_id, '')) <> '')
+      )
+) AS legacy
+JOIN auth_identities AS ai
+  ON ai.provider_type = legacy.provider_type
+ AND ai.provider_key = legacy.provider_key
+ AND ai.provider_subject = legacy.provider_subject
+WHERE ai.user_id <> legacy.user_id
+ON CONFLICT (report_type, report_key) DO NOTHING;
+$sql$;
+
+    EXECUTE $sql$
+INSERT INTO auth_identities (
+    user_id,
+    provider_type,
+    provider_key,
+    provider_subject,
+    verified_at,
+    metadata
+)
+SELECT
+    legacy.user_id,
+    legacy.provider_type,
+    legacy.provider_key,
+    legacy.provider_subject,
+    legacy.verified_at,
+    legacy.metadata_json || jsonb_build_object(
+        'legacy_identity_id', legacy.id,
+        'provider_user_id', legacy.provider_user_id,
+        'provider_union_id', NULLIF(legacy.provider_union_id, ''),
+        'provider_username', legacy.provider_username,
+        'display_name', legacy.display_name,
+        'migration', '116_auth_identity_legacy_external_safety_reports'
+    )
+FROM (
+    SELECT
+        uei.id,
+        uei.user_id,
+        LOWER(BTRIM(COALESCE(uei.provider, ''))) AS provider_type,
+        CASE
+            WHEN LOWER(BTRIM(COALESCE(uei.provider, ''))) = 'wechat' THEN 'wechat-main'
+            ELSE 'linuxdo'
+        END AS provider_key,
+        CASE
+            WHEN LOWER(BTRIM(COALESCE(uei.provider, ''))) = 'wechat' THEN BTRIM(COALESCE(uei.provider_union_id, ''))
+            ELSE BTRIM(COALESCE(uei.provider_user_id, ''))
+        END AS provider_subject,
+        BTRIM(COALESCE(uei.provider_user_id, '')) AS provider_user_id,
+        BTRIM(COALESCE(uei.provider_union_id, '')) AS provider_union_id,
+        BTRIM(COALESCE(uei.provider_username, '')) AS provider_username,
+        BTRIM(COALESCE(uei.display_name, '')) AS display_name,
+        public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) AS metadata_json,
+        COALESCE(uei.updated_at, uei.created_at, NOW()) AS verified_at
+    FROM user_external_identities AS uei
+    JOIN users AS u ON u.id = uei.user_id
+    WHERE u.deleted_at IS NULL
+      AND LOWER(BTRIM(COALESCE(uei.provider, ''))) IN ('linuxdo', 'wechat')
+      AND (
+          (LOWER(BTRIM(COALESCE(uei.provider, ''))) = 'linuxdo' AND BTRIM(COALESCE(uei.provider_user_id, '')) <> '')
+          OR
+          (LOWER(BTRIM(COALESCE(uei.provider, ''))) = 'wechat' AND BTRIM(COALESCE(uei.provider_union_id, '')) <> '')
+      )
+) AS legacy
+LEFT JOIN auth_identities AS ai
+  ON ai.provider_type = legacy.provider_type
+ AND ai.provider_key = legacy.provider_key
+ AND ai.provider_subject = legacy.provider_subject
+WHERE ai.id IS NULL
+ON CONFLICT (provider_type, provider_key, provider_subject) DO NOTHING;
+$sql$;
+
+    EXECUTE $sql$
+INSERT INTO auth_identity_migration_reports (report_type, report_key, details)
+SELECT
+    'legacy_external_channel_conflict',
+    'legacy_external_identity:' || legacy.id::text,
+    legacy.metadata_json || jsonb_build_object(
+        'legacy_identity_id', legacy.id,
+        'legacy_user_id', legacy.user_id,
+        'existing_channel_id', channel.id,
+        'existing_identity_id', existing_ai.id,
+        'existing_user_id', existing_ai.user_id,
+        'provider_type', 'wechat',
+        'provider_key', 'wechat-main',
+        'provider_subject', legacy.provider_union_id,
+        'channel', legacy.channel,
+        'channel_app_id', legacy.channel_app_id,
+        'channel_subject', legacy.provider_user_id,
+        'reason', 'legacy channel subject already belongs to another user',
+        'migration', '116_auth_identity_legacy_external_safety_reports'
+    )
+FROM (
+    SELECT
+        uei.id,
+        uei.user_id,
+        BTRIM(COALESCE(uei.provider_user_id, '')) AS provider_user_id,
+        BTRIM(COALESCE(uei.provider_union_id, '')) AS provider_union_id,
+        public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) AS metadata_json,
+        BTRIM(COALESCE(public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) ->> 'channel', '')) AS channel,
+        BTRIM(COALESCE(
+            public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) ->> 'channel_app_id',
+            public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) ->> 'appid',
+            public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) ->> 'app_id',
+            ''
+        )) AS channel_app_id
+    FROM user_external_identities AS uei
+    JOIN users AS u ON u.id = uei.user_id
+    WHERE u.deleted_at IS NULL
+      AND LOWER(BTRIM(COALESCE(uei.provider, ''))) = 'wechat'
+      AND BTRIM(COALESCE(uei.provider_union_id, '')) <> ''
+      AND BTRIM(COALESCE(uei.provider_user_id, '')) <> ''
+) AS legacy
+JOIN auth_identities AS legacy_ai
+  ON legacy_ai.user_id = legacy.user_id
+ AND legacy_ai.provider_type = 'wechat'
+ AND legacy_ai.provider_key = 'wechat-main'
+ AND legacy_ai.provider_subject = legacy.provider_union_id
+JOIN auth_identity_channels AS channel
+  ON channel.provider_type = 'wechat'
+ AND channel.provider_key = 'wechat-main'
+ AND channel.channel = legacy.channel
+ AND channel.channel_app_id = legacy.channel_app_id
+ AND channel.channel_subject = legacy.provider_user_id
+JOIN auth_identities AS existing_ai
+  ON existing_ai.id = channel.identity_id
+WHERE legacy.channel <> ''
+  AND legacy.channel_app_id <> ''
+  AND existing_ai.user_id <> legacy.user_id
+ON CONFLICT (report_type, report_key) DO NOTHING;
+$sql$;
+
+    EXECUTE $sql$
+INSERT INTO auth_identity_channels (
+    identity_id,
+    provider_type,
+    provider_key,
+    channel,
+    channel_app_id,
+    channel_subject,
+    metadata
+)
+SELECT
+    legacy_ai.id,
+    'wechat',
+    'wechat-main',
+    legacy.channel,
+    legacy.channel_app_id,
+    legacy.provider_user_id,
+    legacy.metadata_json || jsonb_build_object(
+        'openid', legacy.provider_user_id,
+        'unionid', legacy.provider_union_id,
+        'migration', '116_auth_identity_legacy_external_safety_reports'
+    )
+FROM (
+    SELECT
+        uei.user_id,
+        BTRIM(COALESCE(uei.provider_user_id, '')) AS provider_user_id,
+        BTRIM(COALESCE(uei.provider_union_id, '')) AS provider_union_id,
+        public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) AS metadata_json,
+        BTRIM(COALESCE(public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) ->> 'channel', '')) AS channel,
+        BTRIM(COALESCE(
+            public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) ->> 'channel_app_id',
+            public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) ->> 'appid',
+            public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) ->> 'app_id',
+            ''
+        )) AS channel_app_id
+    FROM user_external_identities AS uei
+    JOIN users AS u ON u.id = uei.user_id
+    WHERE u.deleted_at IS NULL
+      AND LOWER(BTRIM(COALESCE(uei.provider, ''))) = 'wechat'
+      AND BTRIM(COALESCE(uei.provider_union_id, '')) <> ''
+      AND BTRIM(COALESCE(uei.provider_user_id, '')) <> ''
+) AS legacy
+JOIN auth_identities AS legacy_ai
+  ON legacy_ai.user_id = legacy.user_id
+ AND legacy_ai.provider_type = 'wechat'
+ AND legacy_ai.provider_key = 'wechat-main'
+ AND legacy_ai.provider_subject = legacy.provider_union_id
+LEFT JOIN auth_identity_channels AS channel
+  ON channel.provider_type = 'wechat'
+ AND channel.provider_key = 'wechat-main'
+ AND channel.channel = legacy.channel
+ AND channel.channel_app_id = legacy.channel_app_id
+ AND channel.channel_subject = legacy.provider_user_id
+WHERE legacy.channel <> ''
+  AND legacy.channel_app_id <> ''
+  AND channel.id IS NULL
+ON CONFLICT DO NOTHING;
+$sql$;
+
+    EXECUTE $sql$
+INSERT INTO auth_identity_migration_reports (report_type, report_key, details)
+SELECT
+    'wechat_openid_only_requires_remediation',
+    'legacy_external_identity:' || legacy.id::text,
+    legacy.metadata_json || jsonb_build_object(
+        'legacy_identity_id', legacy.id,
+        'user_id', legacy.user_id,
+        'openid', legacy.provider_user_id,
+        'reason', 'legacy user_external_identities row only has openid and cannot be canonicalized offline',
+        'migration', '116_auth_identity_legacy_external_safety_reports'
+    )
+FROM (
+    SELECT
+        uei.id,
+        uei.user_id,
+        BTRIM(COALESCE(uei.provider_user_id, '')) AS provider_user_id,
+        public.__migration_116_safe_legacy_metadata_jsonb(uei.metadata) AS metadata_json
+    FROM user_external_identities AS uei
+    JOIN users AS u ON u.id = uei.user_id
+    WHERE u.deleted_at IS NULL
+      AND LOWER(BTRIM(COALESCE(uei.provider, ''))) = 'wechat'
+      AND BTRIM(COALESCE(uei.provider_user_id, '')) <> ''
+      AND BTRIM(COALESCE(uei.provider_union_id, '')) = ''
+) AS legacy
+ON CONFLICT (report_type, report_key) DO NOTHING;
+$sql$;
+END $$;
+
+DROP FUNCTION IF EXISTS public.__migration_116_is_valid_legacy_metadata_jsonb(TEXT);
+DROP FUNCTION IF EXISTS public.__migration_116_safe_legacy_metadata_jsonb(TEXT);