feat(frontend): load URL-encoded scripts on /scripts/add

The "Fork" action on run/[...run] and several workspace-settings
helper-script templates base64-JSON-encode a NewScript into the URL
hash on `/scripts/add#...`. Until now /scripts/add silently dropped
that payload — both call sites landed on a blank editor.

Decode `page.url.hash` at module top, and if it parses to an object,
apply it as `scriptHandle.draft` and surface "Loaded from URL". The
URL value wins over local autosave, ?template, ?hub, and YAML imports
because the hash represents an explicit "open this script" intent.

Parsing is inlined rather than reusing `decodeState` so an unrelated
hash (e.g. a future route anchor) doesn't fire its default "Impossible
to parse state" error toast.

frontend/src/routes/(root)/(logged)/scripts/add/+page.svelte

@@ -34,6 +34,28 @@
 	const collabLang = page.url.searchParams.get('lang') as ScriptLang | null
 	const wacParam = page.url.searchParams.get('wac')
 	const importParam = page.url.searchParams.get('import')
+
+	/** Some pages (run/[...run]'s "Fork" action, workspace_settings'
+	 * error/success-handler template buttons) base64-JSON-encode a NewScript
+	 * payload into the URL hash. That value is an explicit "open this script"
+	 * intent and wins over local autosave, templates, hubs, and YAML imports.
+	 *
+	 * We can't use `decodeState` from utils.ts directly — it fires its own
+	 * "Impossible to parse state" toast on failure, which would noise up the
+	 * UI when the hash isn't a script payload at all (e.g. a route anchor).
+	 */
+	function decodeUrlScript(): Partial<Script> | undefined {
+		const fragment = page.url.hash.startsWith('#') ? page.url.hash.slice(1) : ''
+		if (!fragment) return undefined
+		try {
+			const decoded = JSON.parse(decodeURIComponent(atob(fragment)))
+			if (decoded && typeof decoded === 'object') return decoded as Partial<Script>
+		} catch {
+			// Hash isn't a valid encoded script — ignore.
+		}
+		return undefined
+	}
+	const urlScript = decodeUrlScript()
 	// "+ Script" buttons navigate with ?nodraft=true to signal "start fresh".
 	// Wipe the persisted empty-path autosave and strip the flag from the URL
 	// synchronously so a reload doesn't wipe the freshly-started draft. A
@@ -73,13 +95,20 @@
 		}
 	}
 
-	// templatePath/hubPath/import flows replace the value before render, so
-	// defaultValue is left undefined for those to avoid flashing a blank editor.
+	// templatePath/hubPath/import/url-hash flows replace the value before
+	// render, so defaultValue is left undefined for those to avoid flashing a
+	// blank editor.
 	const scriptHandle = UserDraft.use<Script>('script', '', {
-		defaultValue: templatePath || hubPath ? undefined : defaultScript()
+		defaultValue: templatePath || hubPath || urlScript ? undefined : defaultScript()
 	})
 
+	if (urlScript) {
+		scriptHandle.draft = { ...defaultScript(), ...urlScript }
+		sendUserToast('Loaded from URL')
+	}
+
 	async function loadTemplate(): Promise<void> {
+		if (urlScript) return
 		if (templatePath) {
 			try {
 				const template = await ScriptService.getScriptByPath({
@@ -104,6 +133,7 @@
 	}
 
 	async function loadHub(): Promise<void> {
+		if (urlScript) return
 		if (hubPath) {
 			try {
 				const { content, language, summary } = await ScriptService.getHubScriptByPath({
@@ -128,7 +158,7 @@
 	loadHub()
 
 	let importedWacTemplate: 'wac_python' | 'wac_typescript' | undefined = undefined
-	if (importParam && $importScriptStore) {
+	if (!urlScript && importParam && $importScriptStore) {
 		const imported = $importScriptStore
 		$importScriptStore = undefined
 		const isWac = isWorkflowAsCode(imported.content ?? '', imported.language ?? '')