feat(cursor): implement permission approval for interaction_query

[chenhg5]

Summary

• Implemented permission approval flow for Cursor Agent's interaction_query events
• Added stdin pipe to cursorSession for writing responses back to Cursor process
• Modified handleInteractionQuery to emit EventPermissionRequest for user approval
• Implemented RespondPermission to write interaction_query/response via stdin
• Auto-approve for yolo/force mode, request user approval for default mode

Root Cause

Cursor Agent in default mode was auto-rejecting all tool calls because:

• RespondPermission was a no-op (empty implementation)
• handleInteractionQuery only emitted EventToolUse, not EventPermissionRequest
• Cursor waited for response, timed out, and auto-rejected

Test plan

• go build ./... passes
• go vet ./... passes
• go test ./... passes
• Manual: Cursor Agent in default mode prompts user for tool approval
• Manual: yolo/force mode continues to auto-approve

Closes #785

🤖 Generated with Claude Code

[chenhg5]

Review Summary

Solid implementation of the two-way permission flow for Cursor Agent. This fixes a real and reproducible bug: Cursor's default mode was auto-rejecting all tool calls because RespondPermission was a no-op. CI is green across all 5 checks.

As an owner PR, I can't formally approve — but sharing detailed notes for the record.

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🟡 Protocol: query_type in response may not match Cursor's expected value
File: agent/cursor/session.go, writeJSON call in RespondPermission
Why: The outgoing response hardcodes "query_type": "permission" regardless of the actual incoming query type (shellRequestQuery, webFetchRequestQuery, etc.). If Cursor Agent key-dispatches responses on query_type, it may not route the response back to the correct handler.
Fix: Consider passing queryType through to RespondPermission via core.PermissionResult or a separate field, then echoing the original value in the response.

🟡 response.response.id type mismatch
File: agent/cursor/session.go line ~545
Why: requestID is parsed as float64 from JSON and converted to string via fmt.Sprintf("%d", int(requestID)). If Cursor expects a numeric id in the response payload, sending it as a string may cause a routing failure.
Fix: Confirm Cursor's expected type for id in the response; send as int if needed.

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✅ Good: stdin mutex (stdinMu) prevents concurrent write races correctly.
✅ Good: Auto-approve path in yolo/force mode still emits EventToolUse for visibility — clean separation of concerns.
✅ Good: Failure path in RespondPermission checks cs.alive before writing — avoids write-on-closed-pipe panics.

If the query_type echo and id type are confirmed correct by manual testing (or by inspecting Cursor's source), this is ready to merge.