diff --git a/src/commands/add.ts b/src/commands/add.ts
index 38e578e..00b7f6b 100644
--- a/src/commands/add.ts
+++ b/src/commands/add.ts
@@ -138,7 +138,14 @@ export async function add_site(target: string, options: AddOptions) {
 	// dashboard doesn't invent an ad-hoc group id for it.
 	if (config.group === 'default') {
 		const site_groups = server_config.site_groups ?? []
-		if (!site_groups.some((group) => group.id === 'default')) {
+		// After the first import, server.yaml holds the server's id for the
+		// Default group rather than the `default` slug. Point this site at that
+		// group instead of adding a second "Default".
+		const existing_default = site_groups.find((group) => group.id !== 'default' && group.name.toLowerCase() === 'default')
+		if (existing_default) {
+			config.group = existing_default.id
+			await write_site_config(site_dir, config)
+		} else if (!site_groups.some((group) => group.id === 'default')) {
 			server_config = {
 				...server_config,
 				site_groups: [...site_groups, { id: 'default', name: 'Default', index: site_groups.length }]
diff --git a/src/commands/new.ts b/src/commands/new.ts
index 7f62ab7..d01d7d3 100644
--- a/src/commands/new.ts
+++ b/src/commands/new.ts
@@ -500,6 +500,7 @@ Without the MCP server, read \`sites/*/blocks/*/fields.yaml\` and \`sites/*/page
 - \`primo dev\` — start the local CMS and dev server. Run from the workspace root. It runs until stopped; from scripts or agents, run it in the background and stop it by PID.
 - \`primo new [name]\` — scaffold a new site under \`sites/\`. In an interactive terminal it then starts the CMS; add \`--skip-dev\` to only create files.
 - \`primo add <name>\` — register an existing \`sites/<name>\` folder with the CMS (mints its site_id and imports its records). Creating the folder alone doesn't register it. Stop \`primo dev\` first, then start it again afterwards. A folder copied from another site gets fresh ids automatically.
+- \`primo preview --dir sites/<name>\` — build that site's preview (needs \`primo dev\` running). Until a site's preview is built, its preview URL shows the CMS instead; rebuild after edits to see them there.
 - File edits sync automatically while \`primo dev\` is running. Structural changes (block schema, component) may trigger a browser reload.
 
 ## Shared library
diff --git a/src/utils/server-config.ts b/src/utils/server-config.ts
index 33c01b2..a55f229 100644
--- a/src/utils/server-config.ts
+++ b/src/utils/server-config.ts
@@ -103,7 +103,18 @@ export async function read_server_config(base_dir: string): Promise<ServerConfig
 
 export const DEFAULT_PORT = 3000
 
+// One entry per group id. Older paths could append a second copy of a group
+// (same server id, next index) when a site still referenced the local
+// `default` slug; drop repeats and close the index gaps they leave.
+function dedupe_site_groups(groups: SiteGroupConfig[] | undefined): SiteGroupConfig[] | undefined {
+	if (!groups) return groups
+	const seen = new Set<string>()
+	const unique = groups.filter(group => !seen.has(group.id) && !!seen.add(group.id))
+	if (unique.length === groups.length) return groups
+	return unique.map((group, index) => ({ ...group, index }))
+}
+
 export async function write_server_config(base_dir: string, config: ServerConfig): Promise<void> {
-	const normalized = normalize_server_config(config)
+	const normalized = normalize_server_config({ ...config, site_groups: dedupe_site_groups(config.site_groups) })
 	await fs.writeFile(get_server_config_path(base_dir), dump_yaml(normalized, { lineWidth: -1, noRefs: true }))
 }
diff --git a/tests/group-writeback.test.mjs b/tests/group-writeback.test.mjs
index ea5cb2f..3cd583b 100644
--- a/tests/group-writeback.test.mjs
+++ b/tests/group-writeback.test.mjs
@@ -91,3 +91,15 @@ describe('apply_server_group_id', () => {
 		}
 	})
 })
+
+test('write_server_config keeps one entry per group id and heals existing duplicates', async () => {
+	const { write_server_config, read_server_config } = await import('../dist/utils/server-config.js')
+	const dir = await (await import('node:fs/promises')).mkdtemp((await import('node:path')).join((await import('node:os')).tmpdir(), 'groups-'))
+	await write_server_config(dir, { site_groups: [
+		{ id: 'okwtvqfzrek51by', name: 'Default', index: 0 },
+		{ id: 'okwtvqfzrek51by', name: 'Default', index: 1 },
+		{ id: 'clientsgroup001', name: 'Clients', index: 2 }
+	] })
+	const { site_groups } = await read_server_config(dir)
+	assert.deepEqual(site_groups.map(g => [g.id, g.index]), [['okwtvqfzrek51by', 0], ['clientsgroup001', 1]])
+})