Fix missing RowsAffected checks in cookie update methods

Address PR review comments: capture Exec result and check
RowsAffected() == 0 to return ErrResourceNotFound in
Cookie.Update, CookieCategory.Update, and CookieCategory.UpdateRank.
Also update coredata and relay contributor docs accordingly.

Signed-off-by: Émile Ré <emile@getprobo.com>

contrib/claude/coredata.md

@@ -129,7 +129,13 @@ assets, err := pgx.CollectRows(rows, pgx.RowToAddrOfStructByName[Asset])
 *a = assets
 
 // Update / Delete — no RETURNING
-_, err := conn.Exec(ctx, q, args)
+result, err := conn.Exec(ctx, q, args)
+if err != nil {
+    return err
+}
+if result.RowsAffected() == 0 {
+    return ErrResourceNotFound
+}
 ```
 
 ## Sentinel errors

contrib/claude/relay.md

@@ -341,7 +341,7 @@ Relay directives handle connection updates automatically — no manual store man
 
 #### Connection setup
 
-Any connection that a mutation will add to or remove from **must** have a `@connection` directive and expose `__id`:
+Any connection that a mutation will add to or remove from **must** have a `@connection` directive. If the mutation needs the connection ID in the same fragment, expose `__id`; otherwise derive it with `ConnectionHandler.getConnectionID`:
 
 ```tsx
 const fragment = graphql`

pkg/coredata/cookie.go

@@ -327,7 +327,7 @@ WHERE
 	}
 	maps.Copy(args, scope.SQLArguments())
 
-	_, err := tx.Exec(ctx, q, args)
+	result, err := tx.Exec(ctx, q, args)
 	if err != nil {
 		if pgErr, ok := errors.AsType[*pgconn.PgError](err); ok {
 			if pgErr.Code == "23505" && pgErr.ConstraintName == "idx_cookies_unique_name_per_banner" {
@@ -337,6 +337,10 @@ WHERE
 		return fmt.Errorf("cannot update cookie: %w", err)
 	}
 
+	if result.RowsAffected() == 0 {
+		return ErrResourceNotFound
+	}
+
 	return nil
 }
 

pkg/coredata/cookie_category.go

@@ -341,11 +341,15 @@ WHERE
 	}
 	maps.Copy(args, scope.SQLArguments())
 
-	_, err := tx.Exec(ctx, q, args)
+	result, err := tx.Exec(ctx, q, args)
 	if err != nil {
 		return fmt.Errorf("cannot update cookie category: %w", err)
 	}
 
+	if result.RowsAffected() == 0 {
+		return ErrResourceNotFound
+	}
+
 	return nil
 }
 
@@ -390,11 +394,15 @@ WHERE %s
 	}
 	maps.Copy(args, scope.SQLArguments())
 
-	_, err := tx.Exec(ctx, q, args)
+	result, err := tx.Exec(ctx, q, args)
 	if err != nil {
 		return fmt.Errorf("cannot update cookie category rank: %w", err)
 	}
 
+	if result.RowsAffected() == 0 {
+		return ErrResourceNotFound
+	}
+
 	return nil
 }