feat: implement request_human_approval tool for approval workflow #259
Description
Summary
Per D21, approval requests should be modeled as tool calls (request_human_approval). The approval decision is returned as a ToolResult — semantically correct since approval IS the tool's return value. This tool does not exist yet.
Design Spec Reference
- §12.4 D21 — Resume Injection
Scope
request_human_approvaltool implementation- Integration with approval store
- LLM conversation protocol compliance (tool result after tool call)
- Fallback: system message injection for engine-initiated parking