Fix deep link installation for mods containing + (plus sign) (#6464)

* ffix: preserve literal '+' in deep link URI thru API call

* chore: check for missing projects during installs

* chore: remove accidental test files and quote error ID

* fix rustfmt formatting for the change

apps/app-frontend/src/providers/content-install.ts

@@ -807,6 +807,11 @@ export function createContentInstall(opts: {
 	) {
 		const project: Labrinth.Projects.v2.Project = await get_project(projectId, 'must_revalidate')
 
+		if (!project) {
+			opts.handleError(`Project not found: '${projectId}'`)
+			return
+		}
+
 		if (project.project_type === 'modpack') {
 			const version = versionId ?? project.versions[project.versions.length - 1]
 			const packs = await list()

packages/app-lib/src/state/cache.rs

@@ -1105,8 +1105,15 @@ impl CachedEntry {
                 .collect::<Vec<_>>()
                 .chunks(MAX_REQUEST_SIZE)
                 .map(|chunk| {
-                    serde_json::to_string(&chunk)
-                        .map(|keys| format!("{api_url}{url}{keys}"))
+                    serde_json::to_string(&chunk).map(|keys| {
+                        format!(
+                            "{api_url}{url}{}",
+                            url::form_urlencoded::byte_serialize(
+                                keys.as_bytes()
+                            )
+                            .collect::<String>()
+                        )
+                    })
                 })
                 .collect::<Result<Vec<_>, _>>()?;