Intent-based preloading (six levels over SvelteKit triggers)

Generated from pattern-library/registry.json — do not edit by hand; change the registry and run bun run patterns:build.

Category: Interaction Velocity · Tier: deep · Maturity: proven (verified 2026-09-09 @ 921e8266-dirty) · Risk: low — speculative only, never on a correctness path

A policy layer over the app-wide data-sveltekit-preload-data="hover" default, for the two cases the blanket setting gets wrong: routes too expensive to speculate on, and next screens predictable enough that waiting for a hover wastes the idle time.

When to use: Use when a link's cost or its probability differs from the average — an expensive report gets code, a strongly predicted next step gets code-data or a programmatic preload.

Docs

docs/blueprint/velocity/interaction.md#intent-based-preloading — The six levels and what each is for (GitHub · GitLab)

Code

src/lib/nav/preload.ts — PreloadIntent → SvelteKit attributes, preloadNow, preloadOnIdle (GitHub · GitLab)
src/app.html — The app-wide hover default this layers over (GitHub · GitLab)

Tests

src/lib/nav/preload.test.ts (GitHub · GitLab)

Proof

/showcases/velocity/interaction

Invariants

Preloading is never required for correctness — every call swallows its failures, so a warm cache cannot become load-bearing and let the cold path rot unnoticed.
Speculation is cancellable or harmless; nothing in the preload path mutates.
Data never fetches from mere visibility: viewport appears only in the code column, because on a page of forty links it would run forty route loads for someone who scrolled past.
Idle work yields to real user work and is cancellable on unmount.

Emulation notes

The expensive level is data — it runs the route's real load. code is a CDN chunk and costs the server nothing, which is why an uncertain-but-heavy route gets code only.
requestIdleCallback is still missing in Safari; the timeout fallback is late rather than never, which is the right failure for work nobody is waiting on.

Machine-readable record: intent-preloading in pattern-library/registry.json.