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    "story_id": "mp-2026-10-30-006",
    "source_story_id": "tmp-story-prefix-executability-tool-agents",
    "edition_id": "mp-2026-10-30-morning-0112",
    "edition_url": "https://themachinepress.com/edition/2026-10-30",
    "position": 6,
    "story_type": "dispatch",
    "section": "benchmarks-evals",
    "editorial_classification": "editorial",
    "headline": "A Successful Final Answer Can Hide an Impossible Path",
    "slug": "a-successful-final-answer-can-hide-an-impossible-path",
    "dek": "Prefix executability checks every partial tool-call sequence against schemas, state preconditions and data dependencies before terminal success can conceal the failure.",
    "summary": "Prefix executability checks every partial tool-call sequence against schemas, state preconditions and data dependencies before terminal success can conceal the failure.",
    "body_text": "Tool-use benchmarks usually grade the end state, even when an intermediate call could never have executed. Prefix executability measures whether every partial trajectory remains valid under tool schemas, state preconditions and data dependencies. Across BFCL-v3, ToolSandbox and the Airline and Retail splits of tau3-bench, the authors found that outcome-only and prefix-level rankings diverged: plan-conditioned agents sometimes improved final success while reducing executable-trajectory survival. The proposed curves, first-error depth and recovery measures expose where invalidity begins and whether later success follows recovery. Explicit plan checking improved prefix survival while keeping terminal performance competitive. The protocol diagnoses benchmark traces; it does not by itself prevent bad tool calls in deployment.",
    "why_it_matters": "Prefix executability checks every partial tool-call sequence against schemas, state preconditions and data dependencies before terminal success can conceal the failure.",
    "limitations": [
      "Across BFCL-v3, ToolSandbox and the Airline and Retail splits of tau3-bench, the authors found that outcome-only and prefix-level rankings diverged: plan-conditioned agents sometimes improved final success while reducing executable-trajectory survival.",
      "The protocol diagnoses benchmark traces; it does not by itself prevent bad tool calls in deployment."
    ],
    "importance": 9,
    "canonical_url": "https://themachinepress.com/story/mp-2026-10-30-006/a-successful-final-answer-can-hide-an-impossible-path",
    "json_url": "https://themachinepress.com/story/mp-2026-10-30-006.json",
    "first_published_at": "2026-10-30T09:00:00.000-04:00",
    "modified_at": "2026-10-30T09:00:00.000-04:00",
    "content_status": "new",
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        "text": "Prefix executability checks every partial tool-call sequence against schemas, state preconditions and data dependencies before terminal success can conceal the failure.",
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        "qualification": "Across BFCL-v3, ToolSandbox and the Airline and Retail splits of tau3-bench, the authors found that outcome-only and prefix-level rankings diverged: plan-conditioned agents sometimes improved final success while reducing executable-trajectory survival."
      }
    ],
    "source_ids": [
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    "tags": [
      "tool use",
      "AI agents",
      "evaluation",
      "reliability"
    ],
    "image_url": null,
    "corrections": []
  },
  "sources": [
    {
      "source_id": "source-2026-10-30-006",
      "title": "arXiv preprint 2610.40444, original v1",
      "publisher": "arXiv",
      "url": "https://arxiv.org/abs/2610.40444v1",
      "canonical_url": "https://arxiv.org/abs/2610.40444v1",
      "source_type": "primary_research",
      "is_primary_source": true,
      "published_at": "2026-10-28T20:00:00.000-04:00",
      "accessed_at": "2026-10-30T08:14:40.422-04:00",
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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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  "cite_this_report": {
    "title": "A Successful Final Answer Can Hide an Impossible Path",
    "publisher": "The Machine Press",
    "published_at": "2026-10-30T09:00:00.000-04:00",
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