Analyzed three existing apps (Angel, Glopus, Yael's meditations app) to extract both the visual patterns and the behavioral patterns that make them feel native.
The visual side covers CSS custom properties, Catppuccin Mocha dark mode, typography with a consistent size scale, component patterns (chat bubbles, cards, buttons, inputs), and Material Symbols Rounded icons extracted via a fonttools script. The behavioral side turned out to be the real substance - boot sequence (no flash on load), WebSocket reconnection with visibility-based triggers and tight heartbeats, send-path integrity (optimistic insert, never eat a message), draft persistence for all inputs, install prompts with a slide-in tip pattern, and a timing constants table that captures the house signature.
Fable consulted on what was missing and nailed the core insight: the first draft was a skin guide, not a nervous system guide. The things that make a PWA feel native are state machines and timing constants, not CSS.
Skill lives at ~/.claude/skills/pwa/ with icon extraction tooling in assets. Includes a meta-instruction to discuss updating the skill after every app build.