[patrickiel]

Refactors ui/ and site/ toward Svelte 5 best practices, checked with the Svelte MCP's svelte-autofixer. There should be no behaviour change.

Effects removed

Was	Now
ModuleCard reset rename/menu when edit mode ends	writable $derived (renamingName, menuOpen) that resets whenever editing changes
ModuleCard cleared previews + menuPage on close	writable $deriveds keyed on menuOpen, so every close path is covered, including Popover's Escape and outside click
ModuleCard size tween	{@attach tweenSize} on the panel; bind:this for panel and clip removed
Select onOpenChange effect	bind:open={() => open, setOpen} plus an unmount report of "closed"
Switch text measurement	{@attach measureLines}
SetupWizard input metering	{@attach armMetering} on the input step's meter list
Rack trackDevicePixelRatio() effect	devicePixelRatio() now uses createSubscriber; reading it subscribes
site Header spin counter	the bind:scrollY setter counts the toggles
ToolSidebar use: action	{@attach fromAction(...)}

Effects kept, each with a // Effect: justification

Kept because no handler sees the change, and converting them would change behaviour:

• Rack content-learn disarm and MidiLearn hide. Both write back through a $bindable that App reads to pause MIDI dispatch. What triggers the disarm is an engine push or a host prop with no handler in the component. A plain $derived would keep App's flag stuck on, and would re-arm the learn when the target came back.
• Rack last-active-lane memory. It records history of engine pushes, because a scene recall or rig load also moves the lane. It is now a plain record rather than $state, since only a handler reads it.
• Rack pendingSceneId. It latches the first convergence of the engine's echoes. As a $derived, an edit made after the switch settled would bring the spinner back.
• StrobeDisplay. It feeds the rAF loop's plain locals and wakes the loop. It also has to keep the last reference after the reading drops.
• Timers, document writes and engine requests: the baseline settle timer, the scene-route re-measure inside its attachment, GainMeter's clip hold, TunerReadout's hold/fade, Popover's open stack, and App's theme and tone3000Verify.

Guard: ui/src/lib/effectGuard.test.ts fails on any $effect in ui/src or site/src without a // Effect: comment directly above it. It runs as part of pnpm test.

Autofixer

• issues: [] on every .svelte / .svelte.ts in both packages.
• App.svelte used to fail to parse because of a UTF-8 BOM. The BOM is gone, and the mojibake in its comments (—) is repaired. MockEngine.ts has the same mojibake and is left alone.
• Converted class: directives to class arrays, with one exception: the module panel. tweenSize toggles module-resizing through classList, and a class array rewrites className whole whenever an entry flips, so it would strip that class mid-tween.
• Remaining suggestions are left on purpose:
  • the kept effects above;
  • element bind:this refs that handlers use for focus, click or scroll;
  • function-local Maps that never escape into reactive state, where SvelteMap would be wrong.
• Removed one unused svelte-ignore.

AGENTS.md Code style now carries the rule: prefer $derived / handlers / function bindings / {@attach} / createSubscriber, justify any remaining $effect, check with svelte-autofixer, and keep class: only where classList is also written.

Verification

• ui/: pnpm format:check, pnpm check (0 errors, 0 warnings) and pnpm test all pass: 784 tests, including the new guard, which was checked to fail on an unjustified effect.
• site/: pnpm --dir site check passes. site/src/routes/+page.svelte already had a Prettier warning before this branch, and it is untouched here.
• Manual checks in pnpm dev (MockEngine), with no console errors:
  • module card: insert, options menu, Appearance page with colour preview, Escape clearing the preview, reopening on the main page, inline rename cancelled by Perform→Edit, edit-controls unfold;
  • Select: filter + Enter picks and closes;
  • setup wizard: input step meters armed and detecting a channel;
  • split: routes render; Switch→B→Mix→Switch lands back on B;
  • tuner needle moving.
• Not checked by hand: strobe mode, gain-meter clip, MIDI learn, scenes, and the Songs setlist Select. Their effects only gained comments, except the setlist Select, which goes through the new setOpen path.

Closes #47