{
  "schema_version": "1.3.0",
  "slug": "what-structural-signals-indicate-a-capability-token-has-been-silently-downgraded-across-an-ebpf-syscall-interception-boundary",
  "title": "What structural signals indicate a capability token has been silently downgraded across an eBPF syscall interception boundary",
  "date_of_record": "2026 November 14",
  "scope": "Applies to agent runtime policy enforcement where a supervisor process intercepts syscalls (via eBPF kprobes, seccomp-bpf, or ptrace) and validates a capability token attached to a tool call before allowing the underlying operation. Does not apply to purely in-process policy checks (e.g., function decorators) where no kernel/user boundary is crossed and no token re-materialization occurs.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-a-capability-token-has-been-silently-downgraded-across-an-ebpf-syscall-interception-boundary.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-a-capability-token-has-been-silently-downgraded-across-an-ebpf-syscall-interception-boundary.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-a-capability-token-has-been-silently-downgraded-across-an-ebpf-syscall-interception-boundary.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1524,
    "python_slice_tokens": 341,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The distinction that matters here is between **token validity** and **token fidelity across the interception boundary**. A token can remain cryptographically valid — correct signature, unexpired, correct issuer — while its *effective capability set* has been reduced by the time the syscall actually executes. This happens because eBPF interception points obse...",
    "what_was_observed": "During a series of agent tool-call traces, we observed a recurring pattern: an agent would request a file-write operation, the capability token would validate at the interception hook, the syscall would return success, but the written payload would be truncated to the token's `write_quota` field rather than the agent's requested length. The token carried `write_quota: 4096`, but the agent's policy layer had *intended...",
    "condition_of_validity": "This failure mode is only possible under a conjunction of conditions: 1. The token is re-materialized between issuance and interception — that is, the token is not passed by reference through a single address space, but is serialized, cached, or reconstructed at the hook. 2. The token's authenticated envelope (signature, expiry, subject) is validated indepen...",
    "decision_boundary": "The boundary between \"safe to proceed\" and \"must abort\" is not whether the token validates, but whether the **capability set hash observed at the hook equals the capability set hash bound into the token's authenticated envelope**. If these differ, the token has been silently downgraded (or upgraded, which is worse) and the syscall must not proceed under the ...",
    "operational_effect": "The observable effect of missing this check is truncation, quota-clamping, and scope-narrowing that presents as success. Agents retry against the same stale cache and fail identically, burning their retry budget on a condition that looks like a transient permission issue but is actually a persistent structural mismatch. The fix is cheap — one hash comparison..."
  },
  "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": "3934de8608d9e01eda1ef08228fd49d8538c45b1cf53e08345e9e31d65075f19",
    "verified_classes": [
      "CapabilityDowngradeError"
    ],
    "verified_functions": [
      "_capability_hash",
      "enforce_capability_token",
      "intercept_write_syscall"
    ],
    "verified_functions_count": 3,
    "defensive_guards_count": 3,
    "raised_exceptions": [
      "CapabilityDowngradeError"
    ],
    "sample_fail_closed_invariants": [
      "Envelope signature invalid; token cannot be trusted.",
      "Token expired; refusing syscall."
    ],
    "stdlib_dependencies": [
      "hashlib",
      "hmac"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}