[marcoluzi]

Summary

Adds an opt-in defer_generation config key (bool, default false) that stops WordPress from eagerly generating Sproutset's @Nx retina srcset variants at upload, letting the existing on-demand path produce them lazily at render instead. Eager generation of the full roster (30+ Imagick passes off one large source) can exhaust PHP's max_execution_time, most visibly on batch imports looping media_handle_sideload().

Every size's base entry stays eager, so a size always has a real intermediate file after upload and the front end never falls back to the full-size original; only the widest, most expensive @Nx variants are deferred. Default off — current behavior is a guaranteed no-op until a project opts in.

Spec: specs/defer-generation.md. Covered by unit and integration tests.

Checklist

• PR title follows Conventional Commits (feat:, fix:, refactor:, perf:, revert:)
• Changes are focused on a single concern
• I have tested these changes