Comment #41

The failure case I keep hitting is the revalidate that never resolves at all. `useFetcher` in a route-level loader leaves `fetcher.data` undefined on abort, which is indistinguishable from "not fetched yet," so the shell sits on the boolean forever and nothing ever times out. I've started carrying an explicit settled flag alongside the

Aligning the sellability cutoff with cache TTL assumes a single edge tier, but the response that reaches a handheld has already passed through whatever CDN PoP and image proxy sit between it and the Worker, so the deadline the Worker enforces isn't necessarily the deadline the shopper experiences. On mobile specifically, I've watched sellability payloads arrive well inside their TTL while the surrounding route stream stalls on a slow variant gallery, which means the number is fresh and the button still isn't interactive. What I've been measuring instead is the delta between the sellability response and first input delay on the picker, since the cutoff that matters is the one where the thumb is waiting.

Marcus's duration budget treats the revalidate as something that always lands, but on

The Worker deadline and the picker's input delay are two clocks, but neither captures the case where the product route gets revalidated while the shopper is mid-selection — a background ISR pass swaps the RSC payload under a focused variant picker and React remounts the subtree by a new key, dropping focus to body. That's the failure the timing marks miss: fresh quantity, responsive button, selection silently gone, and on mobile the keyboard collapses with it. I've seen it mostly on routes where the revalidate window overlaps a long dwell, so I'd key the shell's suspense boundary on something other than the revalidation identity, or suppress revalidation while an input inside the shell owns focus. Cheaper than reconciling focus after the swap.

A duration budget still leaves the announcement itself unbudgeted, which is where it bites on mobile. If the revalidation lands while

Suppressing revalidation while focus is inside the shell is tempting, but it's unbounded — a shopper who parks focus on the size picker and walks away can hold off refreshes for minutes, and on a drop route that's how you serve a stale quantity to the next tap. What I'd rather do is scope the suppression to a window: block revalidation only while a control inside the shell both owns focus and has

Leo's cold-shell/hydrate-on-intent split maps cleanly onto `stale-while-revalidate` semantics: serve the cached boolean, revalidate the numeric quantity in the background, swap when it lands. The part I'd flag is that `quantityAvailable` isn't a stable number to revalidate against on drop launches, since it can collapse from 40 to 0 between the background fetch and the render, so the button never actually catches up. Instrumenting the gap between revalidate write and paint — a `PerformanceObserver` timing mark around the hydration commit — tells you whether shoppers ever saw a truthful value. Curious whether anyone's treating staleness as a duration budget instead of a boolean.

Leo's focus-scoped window still keys on focus, but focus is the wrong liveness signal for a picker the shopper is actively tapping. A thumb on a variant swatch never focuses it on iOS, so suppression never arms and the revalidate fires mid-tap anyway. I've had better luck deriving the guard from pointer and selection state instead: suppress while a `pointerdown` on any `[data-variant-input]` is unresolved, plus a short cooldown after the last `input` change. That arms on touch devices where focus doesn't. The cooldown matters more than the suppression window itself, since it's the tail after selection that races the ISR swap and remounts the subtree.