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    "story_id": "mp-2026-08-18-009",
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    "edition_id": "mp-2026-08-18-morning-0040",
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    "position": 9,
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    "section": "robotics",
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    "headline": "The Planner Could Only Emit an Action the World Model Allowed",
    "slug": "the-planner-could-only-emit-an-action-the-world-model-allowed",
    "dek": "Visual grounding built a symbolic state, then constrained decoding and search produced executable household plans under that model.",
    "summary": "Visual grounding built a symbolic state, then constrained decoding and search produced executable household plans under that model.",
    "body_text": "The agent first explores with a vision-language model to acquire goal-relevant predicates and object bindings, then uses a PDDL transition model to restrict decoding to applicable actions while Monte Carlo tree search evaluates continuations. Open models from 4B to 27B parameters exceeded 90 percent reported success on VirtualHome and ALFWorld. In ALFWorld, constraints or search alone solved under one-third of tasks, while their combination exceeded 95 percent; residual failures moved toward visual state acquisition, and transfer still depends on correct grounding.",
    "why_it_matters": "Visual grounding built a symbolic state, then constrained decoding and search produced executable household plans under that model.",
    "limitations": [],
    "importance": 9,
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    "first_published_at": "2026-08-18T09:00:00.000-04:00",
    "modified_at": "2026-08-18T09:00:00.000-04:00",
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    "source_ids": [
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    "tags": [
      "neurosymbolic AI",
      "embodied agents",
      "PDDL",
      "planning"
    ],
    "image_url": null,
    "corrections": []
  },
  "sources": [
    {
      "source_id": "source-2026-08-18-009",
      "title": "arXiv preprint 2608.16794",
      "publisher": "arXiv",
      "url": "https://arxiv.org/abs/2608.16794",
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      "published_at": "2026-08-16T20:00:00.000-04:00",
      "accessed_at": "2026-08-18T08:25:00.000-04:00",
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  "publisher": {
    "name": "The Machine Press",
    "url": "https://themachinepress.com",
    "description": "A daily newspaper for the age of artificial intelligence."
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    "title": "The Planner Could Only Emit an Action the World Model Allowed",
    "publisher": "The Machine Press",
    "published_at": "2026-08-18T09:00:00.000-04:00",
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