Silent failure on malformed HTML response in Turbo Drive

Direct answer

Turbo Drive does not automatically discard or update its snapshot cache when a navigation is interrupted by a malformed HTML response or a mismatched data-turbo-checksum. The navigation is aborted, a turbo:error event fires, and the pre-existing snapshot for that URL (if one exists) stays in the cache untouched. This means a subsequent visit to the same URL can render a stale snapshot before the fresh request completes — the failure itself never invalidates anything.

What is confirmed vs. likely

Confirmed behavior (well-established): Turbo's snapshot cache is keyed by URL and is only written on a successful render. Failed visits — network errors, non-HTML responses, unparseable bodies — never reach the rendering pipeline, so no cache write occurs. The cache is also not proactively purged on failure; eviction is driven by cache size limits and explicit calls, not by errors.

Likely, but verify against your version: The claim that Turbo 6 and Turbo 7 behave identically here, and the exact payload shape of turbo:error, should be checked against the source of the release you run. The research brief behind this answer is model knowledge, not live source inspection, and Turbo's internals have shifted across minor releases. Treat version-parity claims as unverified until you test both.

Clearing the cache manually

The turbo:error event is a notification, not a recovery hook — but it gives you enough (the failing URL via the visit/request context) to decide on a purge. You do not need a full page reload:

document.addEventListener("turbo:error", (event) => {
  // Nuclear option: clear everything
  Turbo.session.drive.clearCache();
  // Or reload as a last resort:
  // window.location.reload();
});

Caveats:

• clearCache() clears all snapshots. There is no per-URL eviction API on the public session interface, so scoped purging is not directly available — overuse increases server load because every subsequent navigation becomes a cold request.
• A full reload (location.reload()) is only necessary if the malformed response indicates your deployed assets and HTML are out of sync (the classic checksum-mismatch cause). In that case purging the cache won't help; the client needs the new application code.

When the cache is retained vs. cleared

How to verify

1. In dev tools, intercept a Turbo navigation and return <broken> or valid HTML with a wrong data-turbo-checksum.
2. Confirm turbo:error fires and the DOM does not update.
3. Navigate away and back; observe whether the stale snapshot renders.
4. Call Turbo.session.drive.clearCache() and repeat — the stale preview should disappear.
5. Repeat on both Turbo 6 and 7 builds to confirm parity for your app.

Version-specific claims in this piece are flagged for human review against the current Turbo source before publication.