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When srcset maxes at 1000w on retina PDP

Sander KorfOctober 1, 20264 min read

PDP packshots looked soft on phones while cards stayed sharp. sizes asked for retina pixels but srcset stopped at 1000w. I matched candidates and one builder.

nextjssanityplaywright+1

Centra incomplete address is permanent

Sander KorfSeptember 30, 20263 min read

A paid Centra order with a blank city blocked our warehouse export queue for eighty minutes. Classify bad address data as permanent and ack the event.

centratypescriptmonorepo

Superseded listen start must not call stop

Sander KorfSeptember 29, 20264 min read

Guided session app granted mic access then showed could not start listening. A stale Listen start called stop and bumped the generation counter past the winner.

reactwebsocketsaudio

Tax estimate is not the creator payout

Sander KorfSeptember 29, 20264 min read

Creator marketplace cards reused a Stripe Tax preview total as payout. Creators read fee plus tax as cash in hand. Split payoutCents from the estimate.

reacttypescriptpayments

Withhold ended LLM steps after move-on

Sander KorfSeptember 24, 20263 min read

Fast models re-showed three resistance memories after move-on. Ended-step instructions must leave the system prompt, not fight a movedOn flag.

llmconvextypescript

Nested Embla: watchDrag and viewport gutters

Sander KorfSeptember 23, 20264 min read

On a Centra PDP, nested Embla carousels for card media and edge-bleed rails hit two traps. Use watchDrag on the parent; safe-area inset on the viewport.

centraemblanextjs+1

Instant Nav needs an SSR shell, not ssr false

Sander KorfSeptember 21, 20263 min read

Fashion liveshow soft nav painted an empty shell. Instant Nav locks static HTML; next/dynamic with ssr false and cookie awaits blocked landmarks e2e needed.

nextjsbambuserperformance

Revalidate type lists, not only references

Sander KorfSeptember 21, 20263 min read

Liveshow detail refreshed after Sanity edits but the overview stayed stale for hours. Type-based GROQ lists never matched reference-only revalidation.

sanitynextjscache

Sparse webhooks need hydrate or a 503 retry

Sander KorfSeptember 21, 20263 min read

BamHub liveshow webhooks sync into Sanity for a public listing. Sparse payloads left shows unpublished until I hydrated from the API or returned 503 for retry.

sanitynextjsbambuser

Late STT must no-op after transcript purge

Sander KorfSeptember 18, 20264 min read

Purge deleted transcript overlays while vendor STT still ran. Completion handlers recreated erased text. Missing overlay row means return, not upsert.

convex

Check both rate limits before you spend

Sander KorfSeptember 18, 20264 min read

STT under per-thread and global Convex buckets spent the thread token when global was empty. Check both before limit and throw so the mutation rolls back.

convex

Map null keys collapse Shopify live variants

Sander KorfSeptember 18, 20263 min read

Shopify PLPs showed wrong Size facets when variant overrides keyed a Map by null shopifyProductId on consolidated locales. Use the store Product GID.

algoliashopifysanity

Algolia v5 replaceAllObjects false-timeouts

Sander KorfSeptember 17, 20264 min read

Fashion full-catalog rebuilds false-fail when replaceAllObjects hits fifty waitForTask polls. Large indexes need a custom copy, batch, and move path.

algolianextjsshopify

RN Modal kills GestureDetector button taps

Sander KorfSeptember 17, 20263 min read

Accept buttons in my Expo app worked everywhere except RN Modal dialogs. GestureDetector taps died silently because Modal renders outside the gesture root.

exporeact-nativegesture-handler

Keep nav backdrop open until close completes

Sander KorfSeptember 16, 20264 min read

On a fashion storefront mega menu, the dim layer snapped off when Base UI cleared the menu value at the start of the exit animation, not the end.

nextjsreacta11y

Nested remote cache breaks Next.js prerender

Sander KorfSeptember 15, 20264 min read

Homepage prerender on a Centra Next.js build failed with 'Filling a cache during prerender timed out'. Nested use cache remote boundaries caused the hang.

nextjscentraperformance

Next redirect 441 in a Cache Components admin

Sander KorfSeptember 14, 20264 min read

Soft-nav to a Convex movement catalog hit React error 441 when a redirect streamed in Suspense. I render the index and pick the default group client-side.

nextjsreactconvex

Centra card video: muted autoplay after mount

Sander KorfSeptember 14, 20263 min read

PLP cards with optional Sanity video stay silent or flash wrong when autoPlay lives in SSR. I start muted loops in a client effect and respect reduced motion.

centrasanitynextjs

Convex Identify reducer before admin UI

Sander KorfSeptember 11, 20264 min read

Clinicians read Identify as a spreadsheet. Engineers cannot prove it ends. I seed Convex, write a pure reducer, and replay the sheet paths in Vitest first.

convexvitesttypescript

Pick a winner when Identify Compare stalls

Sander KorfSeptember 11, 20264 min read

When two movements stay yes after Compare, looping the same chips teaches nothing. I pause for a pick, hatch the losers, and end the run as a hypothesis.

convextypescriptvitest

Lock Identify rules to a typed Convex menu

Sander KorfSeptember 11, 20264 min read

Identify is a clinician movement engine on Convex. Spreadsheet authors invent words weekly; lock metrics and actions to validators so the reducer stays boring.

convextypescript

Klaviyo email video? Poster, not video tag

Sander KorfSeptember 9, 20264 min read

Gmail and Outlook strip video in campaigns. Ship a poster image with an optional play overlay and an outbound link baked at send time from the CMS.

klaviyoreact-emailsanity

Biome bans vendor imports in shop UI

Sander KorfSeptember 9, 20263 min read

On a Centra fashion storefront, product cards broke when commerce API types leaked into JSX. Map to storefront DTOs and ban vendor imports in shop components.

centrasanitybiome+1

Centra CanonicalPath fixes Instant Nav shell

Sander KorfSeptember 8, 20263 min read

Collection pages stuck on loading after Instant Nav. Own PLP slugs per locale, 308 the rest, and skip waiting on empty query strings for the shell.

centranextjsseo

Server-side country labels fix E2E fills

Sander KorfSeptember 8, 20263 min read

Checkout country dropdowns rebuilt after hydration and emptied a test fill. Precompute localized names on the server before the form paints.

intlnextjsplaywright

Centra PDP add to cart stays pressable

Sander KorfSeptember 7, 20264 min read

A fashion PDP that greys out add to cart until size is picked looks broken. Validate on submit, show the hint after a miss, then focus the chips.

centranextjstailwind

Convex session audio purge is terminal-only

Sander KorfSeptember 7, 20263 min read

A research product records session audio apart from chat. Deleting a thread must not wipe the rolls. Admin purge is terminal-only and deletes chunks first.

convexnextjs

Sanity Look pins on a Centra PDP cover crop

Sander KorfSeptember 7, 20263 min read

Editors pin Shop the Look dots on the full photo. A tall cover crop on the product page slides those dots off the garment unless you remap them once.

sanitycentranextjs+1

Centra colour siblings dedupe by uri

Sander KorfSeptember 2, 20264 min read

Colour swatches showed Black twice on a fashion PDP. Dedupe siblings on the URL you paint, then hide the picker when only one colour exists.

centranextjstailwind

Centra size guide transposes the chart

Sander KorfSeptember 2, 20263 min read

Fashion size guides store measurements as rows. Shoppers need size rows on the product page. Flip the sheet once so the numbers match the layout.

centranextjstailwind+1

Centra OOS size swaps the primary CTA

Sander KorfSeptember 2, 20264 min read

An out of stock size on a fashion product page should not grey out checkout. Flip the main button to a notify action and reuse one overlay for every sheet.

centranextjstailwind+1

CSS view() timelines vs IntersectionObserver

Sander KorfSeptember 2, 20264 min read

Below-the-fold blocks on my Next.js site faded in with a client observer. Scroll timelines do the fade now, and older browsers just show the content.

cssnextjstailwind+1

Next.js MDX in HTML, not behind Suspense

Sander KorfSeptember 2, 20264 min read

Crawlers never ran my blog JavaScript, so they got a shell with no article. I flattened the static pages and now test the HTML with scripts turned off.

nextjsmdxplaywright+1

Ship Convex with Vercel Git, not Actions

Sander KorfSeptember 1, 20264 min read

Preview and production disagreed because one push deployed twice. I let Vercel Git own the build, run Convex there, and keep Actions for tests only.

vercelconvexgithub-actions+1

Algolia filter taps paid INP for new objects

Sander KorfAugust 31, 20264 min read

Fashion PLP filter chips felt frozen when an observability hook retried on new object refs each render. Key the effect on queryID, not the results bag.

algoliainstantsearchnextjs+2

Homepage skip links jumped the fold late

Sander KorfAugust 31, 20263 min read

I awaited a cached translation for a skip link and the Shopify homepage jumped. That one string now renders inside the section that already waits.

next-intlnextjssanity+1

Next.js Suspense fallbacks wreck CLS P95

Sander KorfAugust 31, 20263 min read

Empty loading slots made my CMS blocks jump in late and wrecked layout stability. I now reserve height per section type and watch P95, not P75.

nextjssanityshopify+2

Sanity labels hid my Algolia merch pins

Sander KorfAugust 26, 20263 min read

On a fashion storefront PLP, merchandisers pin hero SKUs in Sanity CMS but Algolia ignores them when Groq filters on the desk title instead of the schema id.

algoliasanitynextjs+1

Keep Algolia admin keys off the storefront

Sander KorfAugust 25, 20263 min read

A fashion PLP runs Algolia InstantSearch in the browser. Only the search-only key belongs in client code; writes stay on the server with the admin key.

algoliainstantsearchnextjs+1

Centra to Klaviyo tags need a plugin contract

Sander KorfAugust 22, 20264 min read

Fashion checkout mail never arrives if you invent the event names. Copy the plugin tags and split the catalog id so receipts and restock emails actually send.

centraklaviyo

Dutch Klaviyo receipts arrived in English

Sander KorfAugust 21, 20263 min read

Dutch shoppers got English order emails from Klaviyo. I now pick the storefront language on the server before the event leaves, not in a default template.

next-intlklaviyocentra+1

Staging deep links must not hijack production

Sander KorfAugust 20, 20263 min read

A mobile app ships production and staging builds. Reusing production Universal Link hosts sends QA to the store app and makes staging reset links look broken.

expoeasdeeplinks

EAS SHA-1 fails under Worklets Bundle Mode

Sander KorfAugust 19, 20264 min read

My Expo cloud build died hashing the JS bundle. I pinned Worklets Bundle Mode to false in Babel so Metro stopped hashing a graph I never asked for.

expoeasmetro+1

Reclaim Firebase orphan without password wipe

Sander KorfAugust 18, 20264 min read

An existing email is not always a blank account. I send a password reset when a login already exists, and I only set a password when none is on file.

firebaseexpo

eToro deploy vs rotate: idle cash not rotate

Sander KorfAugust 12, 20268 min read

A live eToro book sat in cash while the allocator returned success. I force a deploy, park leftover in indexes, and name the fee skip when a rotate waits.

etorotrading

eToro search 404: query fields, not ticker

Sander KorfAugust 12, 20264 min read

A live eToro rebalance returned 200 with zero orders. Search 404ed on a bad fields list. I keep the ticker map and treat an empty 200 as the miss.

etoroapiredis

Timed-out eToro opens are at-most-once

Sander KorfAugust 12, 20265 min read

A timeout on an eToro open can still fill the book. I treat open as at-most-once, leave closes on v1, and pick settlement from the matching leverage config.

etoroapi

eToro LLM overlay ±10pp: critic cannot veto

Sander KorfAugust 12, 20264 min read

A live eToro book went to cash when the model rejected the prompt. I keep a fully invested core, cap tilts at ten points, and ignore a critic on idle cash.

etorollmtypescript

Vercel Workflows: skip closed eToro legs

Sander KorfAugust 12, 20264 min read

When a market is closed, I skip that eToro leg instead of retrying the whole Vercel Workflows step. A retry after a partial fill can buy the same names twice.

verceletoroworkflows

Full Stack AI Engineer from Amsterdam

Sander KorfJanuary 2, 20262 min read

I ship agentic Convex workflows and production Gen AI from Amsterdam. Posts cover what I build, who I work with, and what usually breaks in production.

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