L8 Principal Building a Full Stack App From Scratch
In a Nutshell
L8 principal Kun built a complete iOS allowance-tracking app called "Edie's Wallet" from scratch in one session using GPT-5.6 Luna agents orchestrated through Herder and First Mate. He deployed a $5.50/month VPS backend with PostgreSQL and Fastify, implemented Apple Sign-In, and produced a working SwiftUI app that syncs parent-controlled balances to a child read-only view. The workflow relied on parallel agent streams, Lavish interactive planning artifacts, Autonomic Vault for secret authorization, and server-side context compaction to maintain continuity across a 272k-token window.
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Kun, an L8 principal engineer who worked at Meta, Microsoft, and Atlassian, begins building a real project from scratch using his agentic engineering workflow. The project stems from a previous video that received 600,000 views, with viewers requesting a demonstration of building an actual application.
Starting from an empty terminal, Kun launches Herder as his replacement for T-Max to manage agent sessions. He then sets up First Mate, an open source project he created, which allows the captain to communicate with only one agent (the first mate) while the first mate handles all task juggling, reducing cognitive load and context switching.
First Mate is launched using the PI agent harness with the Luna model (GPT 5.6 Luna on X high reasoning level) instead of the default GPT 5.6. The ground rule is established that every task and crew mate will be dispatched to PI agents running this specific model configuration.
Kun activates calm mode in First Mate, which hides all tool calls, scripts, and technical noise, displaying only prompts and responses. This approach works well with modern models where steering is rarely needed, unlike older less intelligent models where observing tool calls was necessary to catch mistakes.
The project is named Edd's Wallet - an app for children to manage allowances. Current methods involve writing in notebooks or relying on memory, which becomes difficult with multiple rules for allowances and spending. The app serves as a balance tracker while teaching basic financial concepts like balance, loans, credit card mechanics, payments, and interest on savings.
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