Register the card in the registry the frontend actually uses - #22
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Home Assistant replaces window.customElements with its own scoped registry while it boots. add_extra_js_url puts the card in the document, so it ran before that swap and defined its elements in a registry the frontend then stopped consulting. The failure was silent: define() succeeded, the module was served with 200 and text/javascript, the banner printed, and window.customCards listed the card because that lives on window rather than on the registry. But customElements.get() returned undefined, the picker did not offer the card, and dashboards using it showed "custom element doesn't exist". Re-importing the identical file after boot worked without raising "already defined", which identified the two registries. Registration now goes through a guarded helper and is repeated when the registry object is exchanged, so a browser that never swaps still registers exactly once. Observed on HA 2026.7.4 with Firefox; adding the card as a Lovelace resource was the workaround, since resources load after the boot.
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Home Assistant replaces window.customElements with its own scoped registry while it boots. add_extra_js_url puts the card in the document, so it ran before that swap and defined its elements in a registry the frontend then stopped consulting.
The failure was silent: define() succeeded, the module was served with 200 and text/javascript, the banner printed, and window.customCards listed the card because that lives on window rather than on the registry. But customElements.get() returned undefined, the picker did not offer the card, and dashboards using it showed "custom element doesn't exist". Re-importing the identical file after boot worked without raising "already defined", which identified the two registries.
Registration now goes through a guarded helper and is repeated when the registry object is exchanged, so a browser that never swaps still registers exactly once. Observed on HA 2026.7.4 with Firefox; adding the card as a Lovelace resource was the workaround, since resources load after the boot.