test: cover the agent-preset wire routes and both restore edges

master moved the RPC surface onto the fetch transport, so the two agentPreset
methods arrived there with nothing driving them. Adds the round trip, plus the
two `recompose` edges that had none: an agent that never composed a preset, so
there is nothing to restore, and a restore that fails because the composition
it reaches for is gone — the roster is a live directory.

Marks the deliberate non-Error rejections in the store specs, which is the
branch they exist to cover.

packages/host/apiproxy/tests/client-handler.spec.ts

@@ -226,6 +226,18 @@ describe('unary round trip', () => {
     expect(appended.result.ok).toBe(true)
   })
 
+  it('routes the agent-preset roster and switch through the wire', async () => {
+    const c = client(scriptedApi())
+
+    const listed = await c.agentPresets.list({})
+    expect(listed.result).toEqual({ ok: true, value: { presets: [] } })
+
+    // The switch carries the session it is about: the host refuses one whose
+    // conversation has started, and it can only know which by id.
+    const selected = await c.agentPresets.select({ sessionId: sid('s1'), agentPreset: 'standard' })
+    expect(selected.result).toEqual({ ok: true, value: { agentPreset: 'standard' } })
+  })
+
   it('passes business errors through as 200 + err result, not a throw', async () => {
     const api = scriptedApi({
       sessions: {