test(client): cover the fixture noteAgentPreset write-back; refresh the module graph

The stub's confirmed-switch write-back landed with the header-label work
but nothing exercised it, and the module graph regen after the master
merge had been swallowed by a silenced generator run.

packages/client/test-runtime/tests/runtime.spec.tsx

@@ -220,6 +220,13 @@ describe('sessions', () => {
       .toMatchObject({ displayTitle: 'renamed', running: true })
     runtime.sessions.setSubagentCatalogOpen('s2' as SessionId, true)
     await runtime.sessions.refreshSubagents('s2' as SessionId)
+    // The confirmed-switch write-back lands on the row it names and ignores
+    // one the fixture never added, exactly as production's list upsert does.
+    runtime.sessions.noteAgentPreset('s1' as SessionId, 'minimal')
+    runtime.sessions.noteAgentPreset('missing' as SessionId, 'minimal')
+    await runtime.flush()
+    expect(runtime.sessions.list.getSnapshot().byId['s1' as SessionId])
+      .toMatchObject({ agentPreset: 'minimal' })
     runtime.sessions.open('s1' as SessionId)
     await runtime.flush()
     expect(runtime.sessions.list.getSnapshot().current).toBe('s1')