fix: support ACP question prompts via extMethod

[hikaruczl]

Summary

• gate ACP question support on both OPENCODE_ENABLE_QUESTION_TOOL and a client-advertised opencode/question capability
• bridge internal question.asked events to ACP clients over extMethod("opencode/question", ...) and reply/reject through the existing question API
• document the extension contract and cover the new flow in ACP event-subscription tests

Validation

• bun test ./test/acp/event-subscription.test.ts
• bun test ./test/tool/question.test.ts
• bun test ./test/acp/agent-interface.test.ts
• bun run typecheck

[github-actions]

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[github-actions]

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my searches, I found one PR that is closely related to the current PR #20016:

Related PR:

• fix(acp): unblock question tool in ACP mode #18657 - fix(acp): unblock question tool in ACP mode (fix(acp): unblock question tool in ACP mode #18657)
  • This PR is directly related as it also addresses question tool functionality in ACP mode. The current PR (fix: support ACP question prompts via extMethod #20016) appears to build upon or enhance this previous fix by adding support for question prompts via extMethod.

The other PRs found (#13750, #17921, #13974) are tangentially related to question tool handling but address different aspects (enabling the tool, handling question.asked events, and preventing hangs).

[hikaruczl]

Closing this fork PR; opening the same changes against sst/opencode instead.