fix: TRAC-284 Coalesce rapid cart quantity/delete clicks#3103
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chanceaclark merged 1 commit intoJul 14, 2026
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Server actions run strictly serially, so rapid clicks on cart quantity +/- or delete buttons queued unboundedly, and navigating away while the queue drained could freeze the page until a hard refresh. Quantity clicks now coalesce into a single absolute-quantity update per line item via a debounced, single-flight dispatcher; deletes are serialized the same way. Each control is still a real progressive-enhancement form (posting straight to the server action) so it keeps working before hydration or if the app bundle fails to load; JS intercepts the submit to route through the dispatcher instead. The cart section is now keyed by cart entityId only (previously entityId-version), since remounting on every mutation could swallow clicks landing during the DOM swap and drop queued actions, leaving the UI stuck pending until a hard refresh. Cart revalidation is unified on revalidateTag (previously a mix of that and revalidatePath). Also fixes the checkout button spinning forever if its navigation is cancelled (Esc, "Stay" on the leave-page prompt, a flaky connection): the URL-string checkout action awaited a promise that never resolved, so a cancelled redirect left retry clicks queued behind a dead action. It now settles after a short timeout or on bfcache restore. Fixes TRAC-284 Co-Authored-By: Claude <noreply@anthropic.com>
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Jira: TRAC-284
What/Why?
Server actions run strictly serially with no abort/parallelism, so rapid clicks on the cart's quantity +/- or delete buttons queued up unboundedly. Combined with optimistic UI, users could click far ahead of the server, and navigating away while the queue drained had historically frozen client-side routing until a hard refresh. See Linear LTRAC-284 for the full prior investigation and options considered.
The fix: a per-line-item pending-intent map + debounced, single-flight dispatcher in
CartClient. Rapid clicks coalesce into one absolute-quantityupdaterequest (replacing the old per-clickincrement/decrementintents, which also collapsed ~150 duplicated lines in the server action into one branch). Deletes flush immediately and are serialized the same way. At most one action is ever in flight, so a failed request only rolls back one gesture instead of an entire queue.Progressive enhancement: each +/-/delete control is its own
display: contentsmicro-form carrying a real, pre-computed absolute quantity (or delete) straight to the server action. Without JS (or before hydration), clicking still works as a normal page round-trip. With JS,onSubmitintercepts and routes through the dispatcher instead. Quantity is clamped server-side only (z.coerce.number().int().min(1)) — no client-side quantity clamp, since thedisabledattribute already prevents decrementing below 1 in every reachable path.Why the cart section is now keyed by
entityIdonly (previouslyentityId-version): keying onversionremounted the whole section on every mutation. React drops actions dispatched into a hook that unmounts before they run, which could deadlock the old design, and clicks landing mid-DOM-swap hit handler-less nodes — this was the actual mechanism behind the "stuck forever" freeze a merchant reported on video. Dispatcher state now lives at the component instance level (not module scope), so if anything ever does remount mid-flight, the failure mode is a harmless snap-back to server truth, not a deadlock.Also fixed: the checkout button spinning forever if its navigation was cancelled (pressing Esc, choosing "Stay" on the leave-page confirm, a dropped connection). The URL-string checkout action awaited a promise around
window.location.assignthat never resolved by design; a cancelled redirect left retry clicks queued behind that dead action forever. It now settles after 8s or onpageshow(bfcache restore), re-enabling the button as a retry.Cart revalidation is also unified on
revalidateTag(TAGS.cart)(previously a mix of that andrevalidatePath('/cart')).This branch went through a full review pass (code-review at high effort with two background verifier agents on timing edge cases, simplify, security-review) before this PR was opened; all findings were resolved and re-verified.
Rollout/Rollback
Standard PR merge to
canary; no feature flag, migration, or experiment involved. Rollback is a straight revert — no schema or data changes.Testing
Verified end-to-end against a live sandbox store with Playwright, covering:
<Stream>/Suspense fallback swap), quantity +/- and delete all work as real page round-trips against the server action.Manual repro steps from the original ticket: add 10+ variants to cart, rapidly click delete/quantity buttons, then click a nav link — no freeze, no hard refresh required.