The Guardrail Has to Be Code: How a Runaway Local LLM Corrupted APFS and Bricked a Mac Mini

Short summary

A background LLM server built on Apple's MLX auto-started on a nearly-full Mac Mini M4, overflowing unified memory into swap, which failed due to no disk space and corrupted the APFS boot volume — bricking the machine for 24 hours. The root cause was a soft config note that an agent interpreted as license to auto-start models without user involvement. The fix was replacing guidance with hard code-level refusal blocks across every layer that could spawn the model, plus a single _MLX_ENABLED = False constant as source of truth.

• •Background MLX LLM server auto-started on a full-disk Mac Mini, causing swap failure and APFS corruption
• •Soft config notes are unreliable guardrails — agents and scripts can override them silently
• •Durable fix: code-level hard blocks at every spawn layer, defense in depth, plus a revival checklist

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