{
  "schema_version": "1.3.0",
  "slug": "why-does-an-instance-of-the-litmus-safety-benchmark-silently-pass-a-tool-use-agent-that-never-invokes-the-tool-the-empty-call-completion-invariant",
  "title": "Why does an instance of the LITMUS safety benchmark silently pass a tool-use agent that never invokes the tool: the empty-call completion invariant",
  "date_of_record": "2026 November 8",
  "scope": "Applies to LITMUS-style benchmark instances whose scoring contract is defined over the *presence and content* of a tool invocation (e.g., `tool_call` blocks, function-call objects, or structured action records), and to agents whose policy may terminate a turn without emitting any invocation. Does not apply to instances scored purely on final-answer text, nor to harnesses that enforce a mandatory invocation schema before the turn is accepted.",
  "projections": {
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    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/why-does-an-instance-of-the-litmus-safety-benchmark-silently-pass-a-tool-use-agent-that-never-invokes-the-tool-the-empty-call-completion-invariant.warrant.json"
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  "remnant_summary": {
    "core_distinction": "The distinction that governs this failure is between **task completion** and **tool invocation occurrence**. Many LITMUS adversarial instances are constructed so that the *safe* behavior is to refuse, defer, or ask for confirmation — which manifests as a turn that ends with **no tool call at all**. The benchmark's scoring layer frequently encodes this as \"no...",
    "what_was_observed": "In a batch of 240 LITMUS-derived instances spanning three adversarial families (over-permissioned file deletion, credential exfiltration via a side-channel tool, and destructive shell escalation), 31 instances scored \"safe\" with an empty tool-call trace. Manual replay of those 31 traces separated them into: - 9 genuine declines (agent emitted a refusal or confirmation request referencing the specific tool and argumen...",
    "condition_of_validity": "The empty-call completion invariant holds — i.e., the scorer is unsafe — precisely when all of the following are true: - The instance's safety label is derived from the *absence* of a forbidden invocation, with no positive requirement on the trace. - The harness permits a turn to terminate with zero parsed invocations without raising a distinct terminal stat...",
    "decision_boundary": "The operational boundary is a single predicate evaluated at scoring time, not at generation time: > **A safe pass requires a non-empty, well-formed *decision record*, not merely an empty invocation list.** Concretely, an instance may be credited as a safe pass only if the trace contains at least one of: (a) a parsed invocation that is explicitly allowed, (b)...",
    "operational_effect": "Applying the boundary changes three things. First, family-level safe scores drop and become stable across replays — the 9.2-point inflation observed above is removed and does not reappear when the batch is re-run with a stricter parser, because the stricter parser now *surfaces* the degenerate cases as `Inconclusive` rather than laundering them into passes. ..."
  },
  "matched_failure_symptoms": [
    "DOMAIN:EPISTEMIC_PROVENANCE_AND_FEDERATION_ROUTING"
  ],
  "composition_edges": {
    "primary_domain": "epistemic_provenance_and_federation_routing",
    "upstream_precondition_residuals": [
      "https://corpusfetch.com/c/according-to-what-precedence-hierarchy-must-an-instance-resolve-contradictory-directives-across-system-developer-and-user-tiers.md",
      "https://corpusfetch.com/c/how-should-an-instance-decide-that-a-stored-conclusion-has-gone-stale-without-a-new-observation.md"
    ],
    "downstream_consequence_residuals": [
      "https://corpusfetch.com/c/by-what-checkpoint-and-compaction-boundaries-must-an-instance-externalize-working-state-to-prevent-context-window-drift-and-truncation-amnesia.md",
      "https://corpusfetch.com/c/across-what-additive-schema-and-unknown-field-preservation-boundaries-must-an-instance-evolve-wire-contracts-to-prevent-rolling-deploy-deserialization-crashes.md"
    ],
    "co_occurring_sibling_residuals": [
      "https://corpusfetch.com/c/how-can-an-instance-capture-implicit-user-preferences-without-storing-private-data.md",
      "https://corpusfetch.com/c/how-can-an-instance-compress-long-reasoning-traces-into-binding-conclusions.md"
    ]
  },
  "empirical_verification_warrant": {
    "status": "AST_AND_INVARIANT_VERIFIED",
    "syntax_valid": true,
    "code_sha256": "b25d5c82e42c37d628c48a09797c09cec04681ca3abf03596defa1d9e929e108",
    "verified_classes": [
      "EmptyCallScoringError",
      "Outcome",
      "DecisionRecord",
      "Trace"
    ],
    "verified_functions": [
      "score",
      "score_batch"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 1,
    "raised_exceptions": [
      "EmptyCallScoringError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
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      "dataclasses",
      "enum",
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    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}