fix(deploy): reject hostnames with trailing hyphens

Tighten the hostname regex to disallow trailing hyphens, which are
invalid per DNS rules and would fail at the API with a confusing error.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: rexxars

packages/@sanity/cli/src/actions/deploy/deployStudio.ts

@@ -237,7 +237,7 @@ function resolveAppHost({
   }
 
   // Validate hostname characters (alphanumeric and hyphens only)
-  if (!/^[a-z0-9][a-z0-9-]*$/i.test(hostname)) {
+  if (!/^[a-z0-9]([a-z0-9-]*[a-z0-9])?$/i.test(hostname)) {
     output.error(
       `Invalid studio hostname "${hostname}". Hostnames can only contain letters, numbers, and hyphens.`,
       {exit: 1},

packages/@sanity/cli/src/commands/__tests__/deploy.studio.test.ts

@@ -1525,6 +1525,25 @@ describe('#deploy studio', () => {
       expect(error?.message).toContain('Invalid studio hostname')
       expect(error?.message).toContain('letters, numbers, and hyphens')
     })
+
+    test('should reject --url with trailing hyphen', async () => {
+      const cwd = await testFixture('basic-studio')
+      process.cwd = () => cwd
+
+      const projectId = 'test-project-id'
+
+      const {error} = await testCommand(DeployCommand, ['--url', 'my-studio-'], {
+        config: {root: cwd},
+        mocks: {
+          cliConfig: {
+            api: {projectId},
+          },
+        },
+      })
+
+      expect(error).toBeInstanceOf(Error)
+      expect(error?.message).toContain('Invalid studio hostname')
+    })
   })
 
   describe('unattended mode', () => {