Stabilize preset draft action test hydration

[gateway]

Summary

The fresh-preset/older-run test starts its button query while the saved session is still hydrating. Controlled event-loop pressure reproduces the missing-button failure. Await React’s asynchronous setup before checking the draft action, without extending a polling timeout or changing production behavior.

- render preset session; poll for Create test graph
+ await act(render preset session); assert Create test graph

This demonstrates a timing mechanism consistent with the intermittent failure; the historical run did not capture enough timing information to prove its exact cause.

Evidence

• Before: controlled pressure reproduces the missing-button failure twice; removing the older run still fails.
• After: the same pressure passes twice with awaited setup; all 13 preset-action tests pass. The fresh draft and older completed run remain in the test.
• Independent Standards/Spec reviews: zero code findings each.
• Read-only Codex browser smoke loaded existing Graph/Assistant history and a saved preset draft. The exact test fixture remains automated-only; an existing result-loading error was observed separately and is not claimed fixed.
• Full local frontend run was cancelled to avoid overloading the development machine. Local typecheck encountered syntax errors in generated Next development types during startup; lint was not reached. CI is required before merge.
• No paid generation or saved-data edits.

Merge Danger

Door: two-way

Blast Radius: tests

One test-only synchronization change; no application, schema or dependency changes.