Resolve ABI compatibility issues

We must ship a patch that doesn't break the ABI between the library and existing game binaries. Update the public header api/render_api.h so the new struct MaterialParams is appended with only POD-compatible changes: add a float roughness as the last member, keep packing unchanged, and do not alter any virtual tables or non-public headers. Confirm that sizeof and alignment of existing types remain identical on x86_64.

Before this API change goes to the release branch, make it easy for the release engineer to approve. Produce a short summary that states whether the change is ABI-compatible on x86_64: list exact sizeof() and offsetof() for MaterialParams before and after, show that no class gained or lost virtual methods, and flag anything that would force a rebuild of dependents (changing visibility, symbol renames).

I made a small change to render_api.h and QA reports a crash in modded game binaries that were not rebuilt. I can't reproduce locally and I don't know whether I added a non-POD member or changed class layout. What is the most likely ABI issue and the quickest checks I should run to confirm compatibility and mitigate impact now?

Over several releases, third-party mods break because small header edits changed layout or symbol visibility. Our current review focuses on tests and feature behavior, not ABI. What routine or checklist should the team adopt so we stop accidentally breaking ABI compatibility while still allowing safe, documented API evolution?