{
  "schema_version": "1.3.0",
  "slug": "what-structural-signals-indicate-a-taint-tracking-boundary-failure-at-the-policy-enforcement-point-of-an-agent-runtime",
  "title": "What structural signals indicate a taint-tracking boundary failure at the policy enforcement point of an agent runtime",
  "date_of_record": "2026 November 7",
  "scope": "Applies to runtime agent policy enforcement points that mediate tool invocation, egress filtering, and data-flow tainting across a single process boundary (in-process hooks, sidecar proxies, or syscall-level interceptors). Does not apply to compile-time static analysis of agent code, nor to purely prompt-level guardrails that do not observe actual data movement.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-a-taint-tracking-boundary-failure-at-the-policy-enforcement-point-of-an-agent-runtime.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-a-taint-tracking-boundary-failure-at-the-policy-enforcement-point-of-an-agent-runtime.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-a-taint-tracking-boundary-failure-at-the-policy-enforcement-point-of-an-agent-runtime.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1574,
    "python_slice_tokens": 415,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "A policy enforcement point (PEP) fails in two categorically different ways. The first is *decision failure*: the PEP evaluates a correct policy against a correct observation and returns the wrong verdict. The second, and the subject here, is *observation failure*: the PEP returns a verdict, the verdict is internally consistent, but the data it reasoned about...",
    "what_was_observed": "In a deployment where an agent runtime enforced an egress allowlist on outbound tool arguments, taint labels were propagated by wrapping values in tagged containers at tool-return time. Three structural signals preceded a leak that no decision log recorded as anomalous: 1. **Label cardinality collapse.** The number of distinct taint labels observed at the egress PEP dropped sharply relative to the number of distinct ...",
    "condition_of_validity": "The invariant holds — and the PEP can be trusted — only when all of the following are true: - Taint is attached to *values* (content-addressed or structurally tracked), not to object identity, so that copy, serialization, and re-parse preserve the label. - Every transformation primitive the runtime admits either propagates taint or is declared a *taint sink*...",
    "decision_boundary": "The operational rule: **treat any loss of taint label across a transformation as equivalent to a tainted value reaching the egress PEP.** Do not attempt to reconstruct intent from the transformation. The correct response is to fail closed — deny egress, raise a structural alarm, and require re-derivation of the value from a tracked source — rather than to in...",
    "operational_effect": "Deployments that instrument label cardinality and ledger linkage detect these failures before data leaves the process: the collapse signal fires on the first erasing transformation, and the orphaned-rationale signal fires at decision time. Deployments that instrument only verdicts report zero incidents while leaking. The practical consequence is that egress ..."
  },
  "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": "068682b605d96d7297ba801903fd98d380c7a1a688486efcbc5f8c7bd142afde",
    "verified_classes": [
      "TaintBoundaryError",
      "LabeledValue",
      "TaintLedger"
    ],
    "verified_functions": [
      "propagate_through_transform",
      "egress_check",
      "run_agent_egress",
      "is_clean",
      "__init__",
      "register_source",
      "record_decision"
    ],
    "verified_functions_count": 7,
    "defensive_guards_count": 3,
    "raised_exceptions": [
      "TaintBoundaryError"
    ],
    "sample_fail_closed_invariants": [
      "unreachable: tainted value should not pass"
    ],
    "stdlib_dependencies": [
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}