Heat Metal vs Constructed Resilience

Incorporated armor can be targeted by the Heat Metal spell (though the warforged itself cannot be directly targeted). It may be somewhat tougher to tell if a warforged has incorporated armor, so it may be possible to attempt the spell on a warforged who hasn’t actually incorporated armor and have the spell fail due to bad targeting. The heavier the armor, the easier it is to spot via Perception: DC 10/15/20 for Heavy/Medium/Light armor as a guideline.
Corollary: Rust Monsters and similar “affects metal objects” effects can target incorporated armor but not the warforged directly.