Resolve and write an absolute OpenCode path when enabling the ingest tool group so systemd services without an interactive PATH can pass ingest readiness checks.
Preserve an existing OBSIDIAN_MCP_INGEST_OPENCODE_PATH across start, token rotation, and tool enable/disable updates instead of dropping it when rewriting the runtime env file.
Validation: python3 -m unittest discover -v; python3 -m py_compile scripts/manage_mcp_service.py tests/test_mcp_service.py; git diff --check; live MCP tools/list and check_ingest_opencode_readiness calls passed after setting the service config.