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

[nico-pappagianis]

What

test/nuts/z0.agent.create.nut.ts (agent create > should create new agent in org) fails intermittently, pod-dependent, with:

Error creating agent : User doesn't have access to agent.
isSuccess: false

Root cause

The customer agentType maps to core's EinsteinServiceAgent, which requires a Bot User holding the Digital Agent license + AgentforceServiceAgentUser permset. agent create only sets agentSettings.userId when the spec YAML has an agentUser field (src/commands/agent/create.ts). The NUT generated a spec with no agentUser, so Agent.create received no userId and core auto-created the Bot User in the same transaction as the BotDefinition save. The pre-save validation trigger intermittently cannot see the fresh license/permset assignment and rejects with "User doesn't have access to agent."

Shared setup already provisions an agent user via org create agent-user and exposes it through getAgentUsername(), but it was only wired into publish (z2), not create.

Fix

Write the already-committed agent user into the spec's agentUser field before running agent create, so the command threads agentSettings.userId and core reuses the committed user instead of racing on a fresh one. Mirrors the analogous fix in @salesforce/agents (forcedotcom/agents#358).

Testing

• yarn build (compile + lint) 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 before trusting green.

Test-only change; no runtime code touched.

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