{
  "schema_version": "1.3.0",
  "slug": "when-must-a-federated-memory-agent-reject-a-differentially-private-retrieval-response-at-the-aggregation-boundary",
  "title": "When must a federated memory agent reject a differentially-private retrieval response at the aggregation boundary?",
  "date_of_record": "2026 November 5",
  "scope": "Applies to federated agent-memory systems where each participant holds a shard of episodic memory, retrieval is performed under secure multi-party computation (MPC), and aggregate results are released under a differential privacy (DP) mechanism (Gaussian or Laplace) before the querying agent consumes them. Does not apply to single-tenant local memory, nor to systems where DP noise is applied at the client before MPC (local-DP) rather than at the aggregator (central-DP).",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/when-must-a-federated-memory-agent-reject-a-differentially-private-retrieval-response-at-the-aggregation-boundary.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/when-must-a-federated-memory-agent-reject-a-differentially-private-retrieval-response-at-the-aggregation-boundary.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/when-must-a-federated-memory-agent-reject-a-differentially-private-retrieval-response-at-the-aggregation-boundary.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1385,
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  },
  "remnant_summary": {
    "core_distinction": "The failure is not \"the DP budget was exceeded\" and not \"the MPC share reconstruction failed.\" Both of those are loudly instrumented. The non-obvious boundary is the **composition of secure retrieval with post-hoc noise addition**: MPC retrieval returns an *exact* aggregate over a *query-dependent* subset of shards, and the DP mechanism is applied to that ex...",
    "what_was_observed": "In a 40-shard deployment with Gaussian DP (σ = 1.2, δ = 1e-6, clip norm 1.0) over a 128-dim embedding aggregate, a querying agent was able to reconstruct, across 300 adaptively chosen queries, the approximate cardinality of the contributing set to within ±2 shards for 94% of queries — despite each returned vector being individually DP-noised. The reconstruction used only the *count of non-zero secure-tally receipts* ...",
    "condition_of_validity": "The aggregation boundary is valid **only if all of the following hold**: - The retrieval set is selected by a mechanism whose output is independent of record *values* (e.g., fixed-shard broadcast, or selection by public metadata), **or** support metadata (receipt counts, contributor identities, tally sizes) is suppressed or itself noised before release. - Th...",
    "decision_boundary": "The agent (or the aggregation gateway acting on its behalf) must reject a retrieval response when **support-channel entropy is not covered by the privacy accountant**, i.e., when the released receipts or tallies reduce the uncertainty about contributor membership below the threshold implied by the declared epsilon. Concretely: reject if `support_leak_bits > ...",
    "operational_effect": "On rejection, the gateway must (a) drop the aggregate and receipts without forwarding to the agent's memory, (b) book the query against the composition accountant as a *released* query only if any channel was emitted — a rejected-but-emitted receipt still counts — and (c) escalate to the shard coordinator to re-run retrieval under a support-safe selection (b..."
  },
  "matched_failure_symptoms": [
    "OOM_KILL_OR_MEMORY_EXHAUSTION"
  ],
  "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": "c883978bc4d7d350804bb1727878611dfba6df6a5cdb62f80f5298f3cd72802f",
    "verified_classes": [
      "SupportPrivacyViolation",
      "RetrievalResponse"
    ],
    "verified_functions": [
      "admit_response"
    ],
    "verified_functions_count": 1,
    "defensive_guards_count": 3,
    "raised_exceptions": [
      "SupportPrivacyViolation"
    ],
    "sample_fail_closed_invariants": [
      "retry released without composition accounting; epsilon would compose unbooked"
    ],
    "stdlib_dependencies": [
      "dataclasses"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}