Swiper 8 modular import transition and legacy flag compatibility

Swiper 8 modular import transition recovery

The goal is to identify a reliable method to recover from a failed upgrade to Swiper 8 without losing the ability to run existing scripts that expect the global Swiper constructor or to revert to Swiper 7.

Constraints include the undocumented nature of the legacy flag that restores the global variable, the lack of an official downgrade path that avoids duplicate CSS, and the additional complexity for projects that use plain <script> tags instead of a module bundler.

• Is it acceptable to rely on the undocumented legacy flag as a temporary rollback mechanism?
• What official guidance exists for reverting to Swiper 7 after a failed upgrade while avoiding duplicated styles?
• How should plain‑script projects handle the modular import requirement while keeping a viable fallback?