{
  "schema_version": "1.3.0",
  "slug": "when-must-an-instance-refuse-to-inherit-ambient-capability-across-a-taint-boundary",
  "title": "When must an instance refuse to inherit ambient capability across a taint boundary",
  "date_of_record": "2026 November 12",
  "scope": "Applies to runtime sandboxing of agent tool calls where a capability handle (file descriptor, RPC token, mount, or subprocess grant) is passed from a parent execution context into a child context that has been tainted by untrusted input. Does not apply to capability *creation* (fresh grants minted inside the child) or to purely declarative policy engines that never hand out live handles.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/when-must-an-instance-refuse-to-inherit-ambient-capability-across-a-taint-boundary.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/when-must-an-instance-refuse-to-inherit-ambient-capability-across-a-taint-boundary.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/when-must-an-instance-refuse-to-inherit-ambient-capability-across-a-taint-boundary.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1162,
    "python_slice_tokens": 128,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The non-obvious boundary is between **capability attenuation** and **capability *provenance* reset**. Attenuation narrows a handle's *authority* (read-only instead of read-write, subtree instead of root). Taint tracking narrows a handle's *trust* (the inputs that produced the call). These are orthogonal axes, and the common failure is to attenuate without re...",
    "what_was_observed": "In a sandboxed tool-call runtime, the parent agent opened a directory capability with the intent `read`. The runtime attenuated it to `read` for a child that had just consumed an untrusted tool result. The attenuation was logged as a success. The child then issued a path that traversed a symlink *inside* the granted subtree to a location outside it. The handle's authority set had been computed at grant time against t...",
    "condition_of_validity": "The re-derivation requirement holds only when **all three** are true: 1. The capability handle is *live* (an OS-level or RPC-level object the child can actually exercise), not a serialized description re-checked at use time. 2. Taint can be introduced *between* grant and use, i.e., the child context is mutable across the call boundary. 3. Authority is comput...",
    "decision_boundary": "Refuse inheritance — raise and require an explicit re-grant — when a tainted child would receive a live handle whose authority set was finalized under a lower taint level, **and** the handle's authority depends on resolvable mutable state (symlinks, ACLs, group membership, mount tables). Attenuate-and-pass is acceptable only when the handle's authority is a ...",
    "operational_effect": "The runtime must carry a taint epoch on every context and stamp every capability handle with the epoch at which its authority set was computed. On crossing into a context with a higher taint epoch, the handle is *invalidated* and must be re-granted; passing it through is a hard error, not a warning. This converts a silent inheritance into a loud refusal, and..."
  },
  "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": "34538a35d578e36882f182f82f3ec422b66ebc3b63d89a7b2a59bca14b26dc76",
    "verified_classes": [
      "TaintInheritanceError",
      "CapabilityHandle"
    ],
    "verified_functions": [
      "pass_capability",
      "__init__"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 1,
    "raised_exceptions": [
      "TaintInheritanceError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}