feat(sdk): add langwatch config to ScenarioConfig for race-condition-free multi-tenant runs

[drewdrewthis]

Summary

• Adds optional langwatch field to ScenarioConfig that takes precedence over env vars
• Eliminates the mutex-guarded process.env mutation pattern required for concurrent multi-tenant scenario execution
• Priority chain: options.langwatch > cfg.langwatch > LANGWATCH_* env vars
• Moves LangwatchConfig type to the domain layer (avoids circular import)
• Adds target: ES2022 to tsconfig to support top-level await in test files

Before:

// Race condition! Must serialize concurrent runs
process.env.LANGWATCH_API_KEY = project.apiKey;
await run({ name, agents, ... });

After:

// Safe for concurrent multi-tenant execution
await run({ name, agents, langwatch: { apiKey: project.apiKey }, ... });

Test plan

• pnpm typecheck — clean
• 20 unit tests pass including 2 new tests:
  • cfg.langwatch used when no options provided
  • options.langwatch takes priority over cfg.langwatch

Closes #203

🤖 Generated with Claude Code

[github-actions]

Automated low-risk assessment

This PR was evaluated against the repository's Low-Risk Pull Requests procedure.

• Scope: Adds LangwatchConfig and a langwatch?: LangwatchConfig on ScenarioConfig, changes EventBus construction to prefer options.langwatch then cfg.langwatch then env vars, moves the LangwatchConfig type to the domain layer, updates tsconfig target to ES2022, and adds unit tests.
• Exclusions confirmed: no changes to auth, security settings, database schema, business-critical logic, or external integrations.
• Classification: low-risk-change under the documented policy.

The changes are limited to adding a LangwatchConfig type and an optional langwatch field on ScenarioConfig, updating the precedence when constructing the existing EventBus (options > cfg > env), moving the type to the domain layer, a tsconfig target bump, and adding tests. It does not modify authentication/authorization logic, database schemas, business‑critical calculations, or change the external API integration itself (only how credentials/config are provided), so it fits the low‑risk criteria. The tsconfig change is a build/test config tweak and the other edits are straightforward and easily reversible.

An approving review has been submitted by automation. The PR may merge once required CI checks pass.

[github-actions]

Approved by automation: PR qualifies as low-risk-change under the documented policy.

[drewdrewthis]

[grinder] READY for human review

CI: green (zero failing, zero pending)
Review: APPROVED by automation (low-risk-change policy)
Threads: zero unresolved

Verified by:
`command gh pr checks 545` → all pass: ci-checks (24.x) pass, javascript-complete pass, python-complete pass
`command gh pr view 545 --json reviewDecision` → "APPROVED"