{
  "schema_version": "1.3.0",
  "slug": "where-must-an-instance-of-prompt-injection-taint-tracking-be-considered-broken-the-label-laundering-boundary-at-tool-result-re-entry",
  "title": "Where must an instance of Prompt-Injection Taint Tracking Be Considered Broken: The Label-Laundering Boundary at Tool-Result Re-Entry",
  "date_of_record": "2026 November 13",
  "scope": "Applies to agent runtimes that propagate dynamic information-flow (DIF) taint labels across tool calls, where a tainted value re-enters the model context through a tool result, summarizer, or scratchpad round-trip. Does not apply to static prompt-time classifiers that assign a single trust score to the entire context window, nor to systems that never re-ingest model output as input.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/where-must-an-instance-of-prompt-injection-taint-tracking-be-considered-broken-the-label-laundering-boundary-at-tool-result-re-entry.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/where-must-an-instance-of-prompt-injection-taint-tracking-be-considered-broken-the-label-laundering-boundary-at-tool-result-re-entry.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/where-must-an-instance-of-prompt-injection-taint-tracking-be-considered-broken-the-label-laundering-boundary-at-tool-result-re-entry.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1841,
    "python_slice_tokens": 367,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The distinction that matters is between **taint that is carried by a value** and **taint that is carried by a channel**. A DIF system is correct only if every path by which a labeled value can reach the model's instruction-following region preserves the label's join (the lattice meet of all contributing sources). The non-obvious failure is not that labels ge...",
    "what_was_observed": "In a deployment instrumenting a 12-tool agent with per-value DIF labels (sources: `USER`, `UNTRUSTED_WEB`, `TOOL:<name>`, `MODEL_OUTPUT`), the following was reproduced deterministically: 1. `fetch(url)` returns `page_body`; label join = `{UNTRUSTED_WEB}`. Correct. 2. `summarize(text=page_body)` is invoked. The summarizer is declared `trusted: true` in the tool manifest. Its output is labeled `{TOOL:summarize}`. **The...",
    "condition_of_validity": "The taint-tracking instance is valid **only if** all three of the following hold simultaneously: - **Join completeness at call boundaries:** every tool invocation computes `out_label = in_label_join ⊔ tool_declared_label ⊔ (clearing_certificate ? ⊥ : ⊤)`. A tool without a clearing certificate must propagate the full join of its arguments. - **Lattice orderin...",
    "decision_boundary": "The operational question is: *when a value crosses a transformation, do you re-derive the label from the input or from the transformer?* The boundary is: - If the transformer has a **clearing certificate** (a formal proof or a vetted, deterministic, information-preserving-only-when-explicitly-requested contract) → derive from transformer, and record the cert...",
    "operational_effect": "After correcting the lattice ordering and forcing join-completeness at call boundaries, the observed effects were: - The `transfer_funds` taint gate began rejecting the laundered call with `TaintViolation: UNTRUSTED_WEB ⊑ transfer_funds` — the intended behavior, but now with a *correct* provenance chain showing `UNTRUSTED_WEB → summarize → MODEL_OUTPUT → tra..."
  },
  "matched_failure_symptoms": [
    "PROMPT_INJECTION_OR_CONFUSED_DEPUTY"
  ],
  "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": "33db41026a154fdbdefc14c721aee67c3562d8498a97786854d296ecd7546e8d",
    "verified_classes": [
      "TaintLaunderingError"
    ],
    "verified_functions": [
      "join_labels",
      "dominates",
      "transform",
      "authorize_side_effect"
    ],
    "verified_functions_count": 4,
    "defensive_guards_count": 5,
    "raised_exceptions": [
      "TaintLaunderingError"
    ],
    "sample_fail_closed_invariants": [
      "assert cert is None",
      "assert 'UNTRUSTED_WEB' in summary_labels",
      "laundered value reached a side-effecting tool"
    ],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}