# `MishkaCmsCore.Runtime.Resources.Changes.PurgePreviewAssets`
[🔗](https://github.com/mishka-group/mishka_cms_core/blob/v0.0.1/lib/mishka_cms_core/runtime/resources/__changes/purge_preview_assets.ex#L5)

Drops a record's cached preview stylesheet after the row is written.

A LIVE RECORD HAS A PREVIEW TOKEN TOO, and its temporary stylesheet is compiled once and cached
under it. `MishkaCmsCore.Runtime.DraftPreviewAssets.ensure_css/2` compiles only when that key is
ABSENT, so a document written with new utility classes went on being previewed against the CSS of
the version before it — the new classes had no rules at all, for the life of the node, and the
reviewer handed the shareable `/_preview/:resource/:token` link read the markup as broken.

ON THE RESOURCE, NOT ON A CALLER, because the callers are many and each one was a separate chance
to forget: the builder's `PageBuilder.Helpers.save_section/4` purged; a draft publish
(`Changes.PublishPageDraft` and its layout / error-page twins), a version restore and the
inspector's Configuration form all wrote the same row and did not. Registered on the update and
destroy types — archiving a document is a soft destroy, and the key of a row nobody can read again
is a leak nothing else will ever drop.

AFTER THE TRANSACTION, NOT AFTER THE ACTION. An `after_action` hook runs while the new row is
still uncommitted, so a preview opened in that window compiles the row as it WAS and stores it
under the key this purge has already dropped — the stale stylesheet back for the life of the node,
which is the whole defect. Purged only when the write succeeded, so a rolled back one keeps its
cache.

DROPPED, NOT RECOMPILED, for the reason `MishkaCmsCore.Runtime.PageBuilder.Drafts` gives: a
Tailwind pass on every save would pay for a preview nobody may open, and `ensure_css/2` already
compiles on the way in.

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*Consult [api-reference.md](api-reference.md) for complete listing*