https://paulund.co.uk Developer notebook — articles on AI, and software engineering. en Mon, 01 Jun 2026 00:00:00 GMT https://paulund.co.uk/notebook/ai/software-factory-build-factories-not-features How senior engineers build software factories: agentic pipelines that autonomously plan, build, validate, and ship features, compounding output over time. Mon, 01 Jun 2026 00:00:00 GMT https://paulund.co.uk/notebook/ai/software-factory-build-factories-not-features https://paulund.co.uk/notebook/ai/small-npm-packages-are-mostly-dead Why AI-generated code replaces the need for small npm packages, and where the line is between a dependency you still need and one an LLM can write on th... Sat, 30 May 2026 00:00:00 GMT https://paulund.co.uk/notebook/ai/small-npm-packages-are-mostly-dead https://paulund.co.uk/notebook/ai/the-four-levels-of-working-with-ai Matt Maher's four-level framework reveals most developers are stuck at level 2. Here is what level 3 looks like in practice and why it matters to move up. Sat, 30 May 2026 00:00:00 GMT https://paulund.co.uk/notebook/ai/the-four-levels-of-working-with-ai https://paulund.co.uk/notebook/ai/what-happens-to-developers-who-dont-adapt-to-ai Which developer skills depreciate and appreciate in 2026, why half-adopting AI is riskier than refusing it, and advice for engineers who feel left behind. Sat, 30 May 2026 00:00:00 GMT https://paulund.co.uk/notebook/ai/what-happens-to-developers-who-dont-adapt-to-ai https://paulund.co.uk/notebook/ai/how-ai-agents-made-me-cli-first How AI agents pulled me into the terminal and changed the way I work. The story of goldcli, automation, and why everything is a command now. Wed, 27 May 2026 00:00:00 GMT https://paulund.co.uk/notebook/ai/how-ai-agents-made-me-cli-first https://paulund.co.uk/notebook/ai/how-i-build-software-with-agent-loops The AI-assisted development workflow I use every day. From HITL planning to AFK implementation, risk-gated PRs, and continuous learning loops. Wed, 27 May 2026 00:00:00 GMT https://paulund.co.uk/notebook/ai/how-i-build-software-with-agent-loops https://paulund.co.uk/releases/goldcli-v110-caching-layer-for-gold-prices goldcli v1.1.0 adds local caching for gold price API responses, cutting redundant requests and keeping you safely inside the 100-request-per-month free ... Tue, 26 May 2026 00:00:00 GMT https://paulund.co.uk/releases/goldcli-v110-caching-layer-for-gold-prices https://paulund.co.uk/notebook/react/higher-order-components-and-why-hooks-replaced-them What higher-order components are, how they worked in class-based React, and why hooks are a better solution for the same problems. Mon, 25 May 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/higher-order-components-and-why-hooks-replaced-them https://paulund.co.uk/notebook/react/pure-components-and-why-purity-matters Learn why React treats your components like pure functions and how keeping renders side-effect free makes your app predictable, testable, and less buggy. Mon, 18 May 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/pure-components-and-why-purity-matters https://paulund.co.uk/notebook/react/fragments-and-when-you-actually-need-them Why React components must return a single root element, how Fragments solve this without polluting the DOM, and the three ways to write them. Mon, 11 May 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/fragments-and-when-you-actually-need-them https://paulund.co.uk/notebook/react/refs-and-when-useref-beats-usestate I used to reach for useState for everything. Here is why useRef is often the better tool for values that do not need to trigger a re-render. Thu, 07 May 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/refs-and-when-useref-beats-usestate https://paulund.co.uk/notebook/react/default-props-optional-props-react How to type optional props in TypeScript and set sensible defaults without reaching for the deprecated defaultProps API. Fri, 01 May 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/default-props-optional-props-react https://paulund.co.uk/notebook/react/handling-form-submission-in-react How to handle form submission in React: async submit handlers, loading states, error display, and resetting the form after success. Thu, 30 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/handling-form-submission-in-react https://paulund.co.uk/notebook/nextjs/client-side-validation-before-server-actions Server Actions do not replace client-side validation. Catch invalid form input early and stop unhandled errors from becoming 500 responses. Wed, 29 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/nextjs/client-side-validation-before-server-actions https://paulund.co.uk/notebook/typescript/type-safe-adapter-registries-with-as-const-and-satisfies Learn how to replace hard-coded service calls with a type-safe adapter registry using TypeScript's as const, satisfies, and derived union types. Wed, 29 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/typescript/type-safe-adapter-registries-with-as-const-and-satisfies https://paulund.co.uk/notebook/typescript/using-service-interfaces-and-null-objects-for-resilient-typescript-scripts How to combine service interfaces, factory functions, and the Null Object pattern to build TypeScript scripts that run safely without credentials or thi... Wed, 29 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/typescript/using-service-interfaces-and-null-objects-for-resilient-typescript-scripts https://paulund.co.uk/notebook/typescript/validating-multi-provider-credentials-with-zod-discriminated-unions How to use Zod's discriminatedUnion to validate per-platform credentials, with a runtime-injected discriminant and TypeScript narrowing at call sites. Mon, 27 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/typescript/validating-multi-provider-credentials-with-zod-discriminated-unions https://paulund.co.uk/releases/paulundai-v310-writing-humanizer-skill v3.1.0 adds a dedicated Writing Humanizer skill to the collection, giving Claude Code a structured way to strip AI-generated patterns from text. Sat, 25 Apr 2026 00:00:00 GMT https://paulund.co.uk/releases/paulundai-v310-writing-humanizer-skill https://paulund.co.uk/notebook/nextjs/building-url-shortener-nextjs How to design the data model, slug generator, and IP hashing for a short-link service using Prisma, Web Crypto, and HMAC-SHA256 for anonymised click tra... Wed, 22 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/nextjs/building-url-shortener-nextjs https://paulund.co.uk/notebook/apis/magic-link-authentication-nextjs How to build passwordless sign-in with email magic links using Supabase Auth, a React Email template, and a clean service wrapper around the OTP flow. Wed, 22 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/apis/magic-link-authentication-nextjs https://paulund.co.uk/notebook/apis/api-key-management-nextjs How to generate, hash, store, and revoke API keys in a Next.js app using SHA-256 hashing, server actions, and cross-project guards. Tue, 21 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/apis/api-key-management-nextjs https://paulund.co.uk/releases/paulundai-v300-skills-only-layout-and-new-skills v3.0.0 removes the Claude plugin system in favour of a flat skills directory, and adds plan, ship, and several developer workflow skills. Tue, 21 Apr 2026 00:00:00 GMT https://paulund.co.uk/releases/paulundai-v300-skills-only-layout-and-new-skills https://paulund.co.uk/notebook/nextjs/transactional-email-resend-react-email How to build a mailer module that renders React Email templates and sends through Resend, with test-time capture so you never send real emails from CI. Tue, 21 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/nextjs/transactional-email-resend-react-email https://paulund.co.uk/notebook/typescript/type-annotations-vs-type-inference TypeScript can infer most types on its own, but knowing when to add an explicit annotation anyway is what separates readable code from a sea of colons. Tue, 21 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/typescript/type-annotations-vs-type-inference https://paulund.co.uk/notebook/react/compound-component-pattern Learn how the compound component pattern lets you build flexible, composable UI components that share state without prop drilling or a complex API. Mon, 20 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/compound-component-pattern https://paulund.co.uk/notebook/react/render-prop-pattern-in-react How the render prop pattern lets you share behaviour between components, why hooks mostly replaced it, and the cases where render props still earn their... Mon, 20 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/render-prop-pattern-in-react https://paulund.co.uk/notebook/react/usereducer-for-complex-state Learn when and how to use useReducer in React to manage state that has multiple related values or transitions that depend on each other. Sun, 19 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/usereducer-for-complex-state https://paulund.co.uk/newsletter/2026-w16 Dynamic OG images, dyslexia and engineering, git codebase reading, and a new Claude Design tool from Anthropic. Sun, 19 Apr 2026 00:00:00 GMT https://paulund.co.uk/newsletter/2026-w16 https://paulund.co.uk/notebook/react/react-context-api-shared-state Learn how to use React's built-in Context API to share state across components without prop drilling or reaching for a third-party library. Sat, 18 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/react-context-api-shared-state https://paulund.co.uk/notebook/nextjs/dynamic-og-images-nextjs How to generate a unique Open Graph image per page at build time using Next.js App Router's opengraph-image.tsx convention, with static export support. Fri, 17 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/nextjs/dynamic-og-images-nextjs https://paulund.co.uk/notebook/react/lifting-state-up-in-react When two components need to share state, you move it to their closest common ancestor. Here's what that looks like in practice and why it works. Fri, 17 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/lifting-state-up-in-react https://paulund.co.uk/notebook/react/conditional-rendering-patterns A practical look at the different ways to conditionally render content in React — when to use each pattern and which ones to avoid. Thu, 16 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/conditional-rendering-patterns https://paulund.co.uk/notebook/react/lists-and-keys-in-react React keys are more than a way to silence a console warning. Understanding how React uses them during reconciliation reveals why the wrong key can intro... Wed, 15 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/lists-and-keys-in-react https://paulund.co.uk/notebook/career/dyslexia-software-engineer A personal essay on how dyslexia shaped debugging instincts, pattern recognition, and systems thinking across a software engineering career. Wed, 15 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/career/dyslexia-software-engineer https://paulund.co.uk/notebook/react/event-handling-in-react How React's event system works, why it differs from vanilla JS, and how to handle clicks, form inputs, and keyboard events correctly — including TypeScr... Tue, 14 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/event-handling-in-react https://paulund.co.uk/notebook/git/git-commands-for-reading-new-codebases Five git commands to run before opening a single file in a new project, revealing churn hotspots, bus factor, bug clusters, and commit velocity. Tue, 14 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/git/git-commands-for-reading-new-codebases https://paulund.co.uk/notebook/react/props-children-and-component-composition Learn how props and the children prop work in React, and how to use component composition to build flexible UIs without tight coupling. Mon, 13 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/props-children-and-component-composition https://paulund.co.uk/notebook/nextjs/queries-layer-nextjs-prisma How to introduce a typed queries layer in a Next.js and Prisma app, moving read functions out of page components to improve discoverability and reuse. Sun, 12 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/nextjs/queries-layer-nextjs-prisma https://paulund.co.uk/notebook/react/react-virtual-dom-reconciliation What the virtual DOM actually is, how React's reconciliation algorithm decides what to update, and why understanding it helps you write faster components. Sun, 12 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/react-virtual-dom-reconciliation https://paulund.co.uk/notebook/react/usestate-mental-model A clear look at what useState actually does in React, why state updates feel async, and how thinking about snapshots stops the confusion. Sat, 11 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/usestate-mental-model https://paulund.co.uk/notebook/react/avoiding-unnecessary-rerenders-in-react How React decides to rerender, where reference equality matters, and the targeted use of memo, useMemo, and useCallback when profiling confirms a problem. Wed, 08 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/avoiding-unnecessary-rerenders-in-react https://paulund.co.uk/notebook/react/composition-over-prop-drilling How to use children as a prop, slot patterns, and component composition to avoid passing props through layers of components that don't care about them. Wed, 08 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/composition-over-prop-drilling https://paulund.co.uk/notebook/react/controlled-vs-uncontrolled-forms-in-react When React-controlled forms with useState make sense, and when uncontrolled refs with useRef are a better fit. The trade-offs are smaller than the debat... Wed, 08 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/controlled-vs-uncontrolled-forms-in-react https://paulund.co.uk/notebook/react/custom-hooks-naming-and-structure How to name, structure, and compose custom hooks so they stay readable and testable. One concern per hook, consistent return shapes, and when to split. Wed, 08 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/react/custom-hooks-naming-and-structure https://paulund.co.uk/notebook/nextjs/deploying-nextjs-to-cloudflare-pages How I deploy a statically exported Next.js 15 site to Cloudflare Pages with GitHub Actions, plus the gotchas around output mode, images, and route handl... Wed, 08 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/nextjs/deploying-nextjs-to-cloudflare-pages https://paulund.co.uk/notebook/nextjs/error-and-not-found-pages-in-app-router The error.tsx and not-found.tsx conventions in the Next.js App Router, how nested error boundaries work, and what happens when notFound() is called. Wed, 08 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/nextjs/error-and-not-found-pages-in-app-router https://paulund.co.uk/notebook/nextjs/fetching-data-in-server-components Patterns for fetching data in Next.js Server Components: direct database access, fetch with caching, parallel requests, and how React deduplicates ident... Wed, 08 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/nextjs/fetching-data-in-server-components https://paulund.co.uk/notebook/nextjs/generatestaticparams-and-static-export How generateStaticParams works with output: 'export' to pre-render every dynamic route at build time, with patterns for nested segments and catch-all ro... Wed, 08 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/nextjs/generatestaticparams-and-static-export https://paulund.co.uk/notebook/nextjs/image-optimisation-in-nextjs How next/image works, the constraints of static export (unoptimized mode), and practical approaches to serve fast images whether you have a server or not. Wed, 08 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/nextjs/image-optimisation-in-nextjs https://paulund.co.uk/notebook/nextjs/incremental-static-regeneration-explained What ISR does, how revalidation works, when ISR is better than full static or dynamic rendering, and what you lose when you move to output: 'export'. Wed, 08 Apr 2026 00:00:00 GMT https://paulund.co.uk/notebook/nextjs/incremental-static-regeneration-explained