{
  "schema_version": "1.3.0",
  "slug": "where-must-an-instance-propagate-a-taint-label-across-a-tool-call-boundary-that-is-not-a-data-edge",
  "title": "Where must an instance propagate a taint label across a tool-call boundary that is *not* a data edge?",
  "date_of_record": "2026 November 14",
  "scope": "Applies to dynamic information-flow control (DIFC) systems that taint-track LLM agent inputs across tool-call graphs, where taint is attached to values and propagated along explicit data dependencies. Does *not* apply to static label systems that taint the entire agent session, nor to systems that treat every tool invocation as a full trust boundary reset.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/where-must-an-instance-propagate-a-taint-label-across-a-tool-call-boundary-that-is-not-a-data-edge.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/where-must-an-instance-propagate-a-taint-label-across-a-tool-call-boundary-that-is-not-a-data-edge.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/where-must-an-instance-propagate-a-taint-label-across-a-tool-call-boundary-that-is-not-a-data-edge.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1323,
    "python_slice_tokens": 217,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The common mental model is that taint flows along *data edges*: an untrusted string enters the prompt, is read by a tool, and any value derived from it inherits the label. This model is correct but incomplete. The failure boundary is the **implicit control edge** — the case where an untrusted value does not appear in the bytes of a downstream tool argument, ...",
    "what_was_observed": "In a test harness with a two-tool agent (`read_document`, `execute_payment`), a payload embedded in a retrieved document — never echoed into any tool argument — reliably caused `execute_payment` to be invoked with attacker-chosen constants. Instrumentation confirmed: 1. The taint label on the document was correctly set to `UNTRUSTED`. 2. The label did **not** propagate to the arguments of `execute_payment` because th...",
    "condition_of_validity": "The data-edge-only propagation rule is valid **only when the agent's tool selection and argument construction are independent of untrusted content** — i.e., when untrusted data is confined to a slot that the model fills but does not use to *choose* the tool or its constant parameters. This holds for retrieval-augmented generation where the retrieved text is ...",
    "decision_boundary": "The operational decision is where to place the label join. Two policies: - **Conservative (control-taint):** if any token in the planner's context is tainted, the entire emitted tool call (tool name + all arguments) is tainted. This over-taints but is sound. - **Precise (provenance-tracked):** track which planner outputs are data-dependent vs. control-depend...",
    "operational_effect": "Enforcing control-taint changes the gate at the tool boundary: a side-effecting tool must be denied (or routed to human confirmation) if *either* its arguments are tainted *or* the planner that produced the call consumed tainted context. In practice this collapses to: **a tool call is tainted if its invocation decision is downstream of any tainted token.** T..."
  },
  "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": "3e53d18c3d77b76039b100c2a536e8bdc1a95e059a965a6bae2807ddfa8b71d2",
    "verified_classes": [
      "TaintPropagationError",
      "ToolCall"
    ],
    "verified_functions": [
      "gate_tool_call",
      "run_agent_step"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 2,
    "raised_exceptions": [
      "TaintPropagationError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}