Using it in a plugin

• Part of: LH idb-keyval

A consuming plugin bundles the library in assets/lib/idb-keyval/ (index.js, umd.js, LICENSE) and copies snippets/lh-idb-keyval-fallback.php verbatim to includes/lh-idb-keyval-fallback.php. Never edit the copy: change the canonical snippet, bump its snippet version and recopy it everywhere. There is no Requires Plugins header, so the consumer stays independent and releasable.

What the snippet does

• Fallback check: lh_idb_keyval_use_fallback() is true when LH idb-keyval has not fired lh_idb_keyval_registered, so a plugin turned off by its init filter counts as inactive.
• Registration: lh_idb_keyval_register_fallback() registers the bundled copy only in that case.
• Registry: records each plugin using its own copy, with the version, in registration order. Only the first copy registers, as a script module ID can only be registered once.
• Site Health: one recommended test, added by whichever plugin loads the snippet first, lists those plugins and, when their versions differ, names the version every plugin is actually getting.
• Plugins screen: each such plugin’s row shows Using bundled idb-keyval x.y.z.
• Service workers: lh_idb_keyval_get_umd_url() returns the shared classic build when LH idb-keyval is active, otherwise the plugin’s own.

No admin notices and no debug-log output.