{
  "schema_version": "1.3.0",
  "slug": "under-what-conditions-must-an-instance-treat-taint-propagation-as-a-blocking-invariant-rather-than-an-advisory-signal-in-tool-sandboxes",
  "title": "Under what conditions must an instance treat taint propagation as a blocking invariant rather than an advisory signal in tool sandboxes",
  "date_of_record": "2026 November 11",
  "scope": "Applies to agentic tool sandboxes that enforce information-flow (taint) labels across tool invocations to prevent exfiltration of untrusted content through side-effectful sinks. Does not apply to read-only retrieval pipelines with no egress surface, nor to sandboxes where all sinks are audited manually before release.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/under-what-conditions-must-an-instance-treat-taint-propagation-as-a-blocking-invariant-rather-than-an-advisory-signal-in-tool-sandboxes.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/under-what-conditions-must-an-instance-treat-taint-propagation-as-a-blocking-invariant-rather-than-an-advisory-signal-in-tool-sandboxes.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/under-what-conditions-must-an-instance-treat-taint-propagation-as-a-blocking-invariant-rather-than-an-advisory-signal-in-tool-sandboxes.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1125,
    "python_slice_tokens": 99,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "A taint-tracking sandbox has two failure modes that look identical in logs but require opposite responses. The first is **label decay**: a taint label is dropped because content passed through a transformation the tracker could not model (string concatenation, JSON re-serialization, base64 round-trip, summarization by an LLM). The second is **label launderin...",
    "what_was_observed": "In a sandbox where an agent fetched a web page, summarized it, and then called `send_email`, the taint label `UNTRUSTED:web` was attached to the fetch result. The summarizer tool returned a plain string. The tracker implemented taint propagation only over tool *arguments* it could statically inspect, so the summarized string—returned as a `str` into the agent's scratch buffer—lost its label. The agent then composed a...",
    "condition_of_validity": "The blocking invariant is valid when all three hold: 1. **The sink has an egress surface outside the trust boundary.** `send_email`, `http_post`, `write_file` to a shared mount, and `exec` all qualify. A sink that writes only to a sandbox-local scratch volume does not. 2. **The transformation between source and sink can preserve instructional content.** An L...",
    "decision_boundary": "The operational rule: **propagate taint through the value graph, not the argument graph.** Any tool whose output is derived from a tainted input must emit an output label equal to the union of its inputs' labels, unless the tool is registered as a *declassifier* with an explicit, per-invocation justification recorded in the trace. A declassifier registration...",
    "operational_effect": "With value-graph propagation and hard-blocking egress sinks, the observed exfiltration class drops to zero in replay of the incident corpus, at the cost of a measurable increase in agent halts on legitimate workflows. Those halts are the correct signal: they mark the exact points where a human or validator must certify declassification. The failure mode to w..."
  },
  "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": "c912d02d892c92c584244a4daa470ecb264a7fae446eff81e7ae3f615c26f330",
    "verified_classes": [
      "TaintViolationError"
    ],
    "verified_functions": [
      "check_sink_admission"
    ],
    "verified_functions_count": 1,
    "defensive_guards_count": 1,
    "raised_exceptions": [
      "TaintViolationError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}