test: fix flaky legacy-layout agent create NUT (Bot User race)

[nico-pappagianis]

What

The agent create > should retrieve the legacy Bot / GenAiPlanner layout ... NUT (test/nuts/agent.nut.ts) fails intermittently, pod-dependent, with:

Error creating agent : User doesn't have access to agent.
isSuccess: false   // expected false to equal true

Root cause

The customer agentType maps to core's EinsteinServiceAgent, which requires a Bot User holding the Digital Agent license + AgentforceServiceAgentUser permset. When Agent.create is called with no agentSettings.userId, core auto-creates that Bot User in the same transaction as the BotDefinition save; the pre-save validation trigger intermittently cannot see the just-created license/permset assignment and rejects with "User doesn't have access to agent."

The describe's before hook already pre-provisions a Bot User, assigns the permset, and waits for the assignment to commit (waitForPermSetAssignment), storing it in botUserId. The sibling should create an agent from a spec test already passes userId: botUserId; this legacy test never got the same fix.

Fix

Pass userId: botUserId in the legacy test's agentSettings so core reuses the already-committed user instead of racing on a fresh one.

Testing

• yarn tsc -b passes.
• The NUT needs a scratch org + default dev hub, not run in this environment. Because the failure is a race, verify with several runs across pods:

  TESTKIT_HUB_USERNAME="<devhub>" yarn mocha "test/nuts/agent.nut.ts" --grep "agent create" --timeout 1800000 --slow 4500

Test-only change; no runtime code touched.

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