LLM Planner Repeated Same 3 Structural Errors Regardless of Model Size

A field test of PlannerCritic, an open-source engine pairing one LLM to write plans with another to review them, uncovered 132 blockers across 63 strict goals. The failures consistently fell into three categories: unverified dependencies, unsafe task sequencing, and weak rollback provisions. Switching to GPT-4o produced better-written plans but did not eliminate any of these structural defects. The developer concluded the root cause was a planning-structure problem rather than insufficient model capacity. The proposed fix is deterministic validation logic, not larger or more capable language models.