Sync kit docs (#1483)

sync kit docs

Co-authored-by: svelte-docs-bot[bot] <196124396+svelte-docs-bot[bot]@users.noreply.github.com>

Author: github-actions[bot]

apps/svelte.dev/content/docs/kit/30-advanced/50-server-only-modules.md

@@ -48,15 +48,18 @@ export const add = (a, b) => a + b;
 ...SvelteKit will error:
 
 ```
-Cannot import $lib/server/secrets.js into public-facing code:
-- src/routes/+page.svelte
-	- src/routes/utils.js
-		- $lib/server/secrets.js
+Cannot import $lib/server/secrets.ts into code that runs in the browser, as this could leak sensitive information.
+
+ src/routes/+page.svelte imports
+  src/routes/utils.js imports
+   $lib/server/secrets.ts
+
+If you're only using the import as a type, change it to `import type`.
 ```
 
 Even though the public-facing code — `src/routes/+page.svelte` — only uses the `add` export and not the secret `atlantisCoordinates` export, the secret code could end up in JavaScript that the browser downloads, and so the import chain is considered unsafe.
 
-This feature also works with dynamic imports, even interpolated ones like ``await import(`./${foo}.js`)``, with one small caveat: during development, if there are two or more dynamic imports between the public-facing code and the server-only module, the illegal import will not be detected the first time the code is loaded.
+This feature also works with dynamic imports, even interpolated ones like ``await import(`./${foo}.js`)``.
 
 > [!NOTE] Unit testing frameworks like Vitest do not distinguish between server-only and public-facing code. For this reason, illegal import detection is disabled when running tests, as determined by `process.env.TEST === 'true'`.
 

apps/svelte.dev/content/docs/kit/30-advanced/68-observability.md

@@ -95,3 +95,7 @@ sdk.start();
 ```
 
 Now, server-side requests will begin generating traces, which you can view in Jaeger's web console at [localhost:16686](http://localhost:16686).
+
+## `@opentelemetry/api`
+
+SvelteKit uses `@opentelemetry/api` to generate its spans. This is declared as an optional peer dependency so that users not needing traces see no impact on install size or runtime performance. In most cases, if you're configuring your application to collect SvelteKit's spans, you'll end up installing a library like `@opentelemetry/sdk-node` or `@vercel/otel`, which in turn depend on `@opentelemetry/api`, which will satisfy SvelteKit's dependency as well. If you see an error from SvelteKit telling you it can't find `@opentelemetry/api`, it may just be because you haven't set up your trace collection yet. If you _have_ done that and are still seeing the error, you can install `@opentelemetry/api` yourself. 

apps/svelte.dev/content/docs/kit/98-reference/[email protected]

@@ -3928,6 +3928,37 @@ type PrerenderOption = boolean | 'auto';
 
 </div>
 
+## PrerenderUnseenRoutesHandler
+
+<div class="ts-block">
+
+```dts
+interface PrerenderUnseenRoutesHandler {/*…*/}
+```
+
+<div class="ts-block-property">
+
+```dts
+(details: { routes: string[]; message: string }): void;
+```
+
+<div class="ts-block-property-details"></div>
+</div></div>
+
+## PrerenderUnseenRoutesHandlerValue
+
+<div class="ts-block">
+
+```dts
+type PrerenderUnseenRoutesHandlerValue =
+	| 'fail'
+	| 'warn'
+	| 'ignore'
+	| PrerenderUnseenRoutesHandler;
+```
+
+</div>
+
 ## Prerendered
 
 <div class="ts-block">

apps/svelte.dev/content/docs/kit/98-reference/50-configuration.md

@@ -1114,6 +1114,34 @@ How to respond when an entry generated by the `entries` export doesn't match the
 </div>
 <div class="ts-block-property">
 
+```ts
+// @noErrors
+handleUnseenRoutes?: PrerenderUnseenRoutesHandlerValue;
+```
+
+<div class="ts-block-property-details">
+
+<div class="ts-block-property-bullets">
+
+- <span class="tag">default</span> `"fail"`
+- <span class="tag since">available since</span> v2.16.0
+
+</div>
+
+How to respond when a route is marked as prerenderable but has not been prerendered.
+
+- `'fail'` — fail the build
+- `'ignore'` - silently ignore the failure and continue
+- `'warn'` — continue, but print a warning
+- `(details) => void` — a custom error handler that takes a `details` object with a `routes` property which contains all routes that haven't been prerendered. If you `throw` from this function, the build will fail
+
+The default behavior is to fail the build. This may be undesirable when you know that some of your routes may never be reached under certain
+circumstances such as a CMS not returning data for a specific area, resulting in certain routes never being reached.
+
+</div>
+</div>
+<div class="ts-block-property">
+
 ```ts
 // @noErrors
 origin?: string;