feat(zones): a blank dome stack is 3 spheres, not 1 (runicnpc 9e, D326)

The org lead chose 3 by eye at noon in RunicNPC's 9d player session. The
zone step sends it when its stack is left blank, and the field's hint says
so. The wire is unchanged: the module always sends a stack, and the bridge's
own default for a dome without one stays 1.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

server/test/zones.test.js

@@ -224,6 +224,16 @@ test('a zone crosses with its flags, settings, messages in the chat voice, and i
   })
 })
 
+test('a dome with its stack left blank stacks 3 spheres (D326)', async (t) => {
+  stubZones(t, { servers: [server('main', { domes: PATCHED })] })
+  const calls = stubWorld(t)
+  const result = await action('rust.zone.open').perform({
+    runId: 7, idempotencyKey: 'k', params: { monument: 'main/a', radius: 40, minutes: 5, dome: 'standard', domeStack: '' },
+  })
+  assert.strictEqual(result.ok, true, result.error)
+  assert.deepStrictEqual(calls[0].body.dome, { type: 0, stack: 3 })
+})
+
 test('a zone with no options crosses exactly as it always did', async (t) => {
   stubZones(t)
   const calls = stubWorld(t)