"Why are coding agents so dumb?": mtlynch argues the harness, not the model, is now the bottleneck

A daily OpenCode and Claude Code user says agents still run parallel subtasks one at a time, never hand gruntwork to cheaper models, write hard-to-read plans, stall overnight on trivial questions, and lack real OS-level sandboxes. He lists table stakes he wants out of the box, including per-task model routing, deterministic filesystem and network boundaries, and an AFK mode that decides after 30 minutes without a reply.