fix: Suppress spinner on same-route navigation in layout (#3338)

.claude/rules/svelte-components.md

@@ -37,6 +37,20 @@ Import from `flowbite-svelte`. Use Tailwind CSS v4 utility classes. Dark mode: `
 
 When copying button styles from a reference component, always check all three axes: `color`, `size`, and `class`. Omitting `color` applies Flowbite's default (filled blue).
 
+## Complex `{#if}` Conditions — Extract to Named Functions
+
+When a template condition requires API-specific knowledge or combines multiple null checks, extract it to a private function in `<script>`. A named function communicates intent at the call site; the implementation detail stays in one place. This applies even when the function is used only once.
+
+```svelte
+<!-- Bad: requires knowing $app/state's null semantics to understand -->
+{#if navigating.from !== null && navigating.from.route.id !== navigating.to?.route.id}
+
+<!-- Good: intent readable without knowing the API -->
+function isCrossRouteNavigation(): boolean { ... }
+
+{#if isCrossRouteNavigation()}
+```
+
 ## `{@const}` Placement
 
 `{@const}` must be an **immediate child** of a block statement (`{#if}`, `{#each}`, `{:else}`, `{#snippet}`, etc.). Placing it inside an HTML element is a compile error:

.claude/rules/sveltekit.md

@@ -73,6 +73,12 @@ const grade = gradeRaw as TaskGrade;
 
 The same pattern applies to `url.searchParams.get()` in `+server.ts` handlers.
 
+## `$app/state`: navigating Idle Check
+
+`navigating` from `$app/state` always exists as an object. Use `navigating.from === null` to detect the idle state — not `navigating === null`.
+
+To limit spinner display to cross-route navigation only, compare `navigating.from.route.id` with `navigating.to?.route.id`. Same-route query-param changes produce equal ids.
+
 ## Page Component Props
 
 SvelteKit page components (`+page.svelte`) accept only `data` and `form` as props (`svelte/valid-prop-names-in-kit-pages`). Commented-out features that reference other props are not "dead code" — remove only the violating prop declaration, preserve the feature code.

src/routes/+layout.svelte

@@ -2,8 +2,7 @@
   // See:
   // https://github.com/oekazuma/svelte-meta-tags
   // https://oekazuma.github.io/svelte-meta-tags/ja/migration-guide/
-  import { page } from '$app/state';
-  import { navigating } from '$app/stores';
+  import { navigating, page } from '$app/state';
 
   import { MetaTags, deepMerge } from 'svelte-meta-tags';
 
@@ -20,6 +19,16 @@
   let { data, children } = $props();
 
   let metaTags = $derived(deepMerge(data.baseMetaTags, page.data.pageMetaTags));
+
+  // $app/state's navigating has from === null when no navigation is occurring (unlike $app/stores
+  // where the entire object is null). route.id is a route path pattern (e.g. "/workbooks"),
+  // so same-route param changes produce equal ids and do not trigger the spinner.
+  //
+  // See:
+  // https://svelte.dev/docs/kit/$app-state#navigating
+  function isCrossRouteNavigation(): boolean {
+    return navigating.from !== null && navigating.from.route.id !== navigating.to?.route.id;
+  }
 </script>
 
 <Header />
@@ -29,9 +38,7 @@
 
 <ErrorMessageToast errorMessage={$errorMessageStore} />
 
-<!-- See: -->
-<!-- https://svelte.dev/docs/kit/$app-stores#navigating -->
-{#if $navigating}
+{#if isCrossRouteNavigation()}
   <SpinnerWrapper />
 {:else}
   {@render children?.()}