fix: require structured blocking questions

[MattPua]

Problem

Agents can end a turn with a plain-text blocking question, causing the task to appear finished instead of waiting for user input.

Changes

• Require AskUserQuestion for blocking questions in the default system prompt
• Add regression coverage for the prompt guidance

How did you test this?

• pnpm exec biome check packages/workspace-server/src/services/agent/agent.ts packages/workspace-server/src/services/agent/agent.test.ts
• pnpm --filter @posthog/workspace-server exec vitest run src/services/agent/agent.test.ts
• pnpm --filter @posthog/workspace-server typecheck
• Pre-commit pnpm typecheck

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

[trunk-io]

😎 Merged successfully - details.

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit dc0d803.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix: document question tools for both ad..." | Re-trigger Greptile}