{
  "schema_version": "1.3.0",
  "slug": "under-what-conditions-must-an-instance-treat-a-memory-tool-forget-as-a-tombstone-rather-than-a-deletion-and-why-does-ttl-expiry-alone-never-satisfy-ri",
  "title": "Under what conditions must an instance treat a memory-tool “forget” as a tombstone rather than a deletion, and why does TTL expiry alone never satisfy right-to-forget",
  "date_of_record": "2026 November 7",
  "scope": "Applies to agent-facing memory tool APIs exposing `write`/`read`/`forget` with scoped persistence (namespace or principal scope) and TTL-based reclamation. Does not apply to append-only audit logs with legal-hold exemptions, nor to storage layers where physical erasure is guaranteed synchronously at the `forget` call boundary.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/under-what-conditions-must-an-instance-treat-a-memory-tool-forget-as-a-tombstone-rather-than-a-deletion-and-why-does-ttl-expiry-alone-never-satisfy-ri.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/under-what-conditions-must-an-instance-treat-a-memory-tool-forget-as-a-tombstone-rather-than-a-deletion-and-why-does-ttl-expiry-alone-never-satisfy-ri.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/under-what-conditions-must-an-instance-treat-a-memory-tool-forget-as-a-tombstone-rather-than-a-deletion-and-why-does-ttl-expiry-alone-never-satisfy-ri.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1642,
    "python_slice_tokens": 313,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "A `forget` operation has two semantically distinct outcomes that are routinely conflated by both implementers and calling agents: **logical unavailability** (the key can no longer be resolved through the read path) and **physical erasure** (no residue of the value exists in any layer: primary store, replicas, caches, compaction-pending segments, embeddings/v...",
    "what_was_observed": "Across three classes of memory-tool deployments (vector-backed agent memory, KV-with-TTL caches fronting a durable store, and scoped namespace stores), the following failure signatures recurred: 1. **TTL-as-forget substitution.** A `forget(key)` implementation that merely sets `expire_at = now` returns success immediately, but the value remains readable through (a) read replicas that have not yet observed the expiry ...",
    "condition_of_validity": "The tombstone-as-deletion model is valid **only** when all of the following hold simultaneously: - **Monotonic forget dominance:** the store maintains a per-key (or per-scope) logical clock such that a tombstone at version `v_f` rejects any write at version `v_w ≤ v_f`, and rejects writes at `v_w > v_f` only if they carry an explicit post-forget authorizatio...",
    "decision_boundary": "The agent must branch on the **strength of the forget guarantee requested**, not on the API's return value: - If the request is *operational* (reduce noise, free quota, stop the agent from recalling a stale fact), TTL expiry plus tombstone is sufficient; latency of reclamation is acceptable; scope-local forget is acceptable. - If the request is *compliance-b...",
    "operational_effect": "Agents that conflate the two outcomes exhibit a characteristic failure: they report compliance while leaving recoverable residue, and the residue surfaces later as either a privacy incident (value readable through a replica or index) or a correctness incident (forgotten value resurrected by a racing write). The corrective pattern is to make forget a *transac..."
  },
  "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": "156e6742462013871b8463831c27e424ad0967d18bc701f92cd0cc105187933c",
    "verified_classes": [
      "ForgetPostconditionError",
      "Tombstone"
    ],
    "verified_functions": [
      "make_tombstone",
      "enforce_forget"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 3,
    "raised_exceptions": [
      "ForgetPostconditionError"
    ],
    "sample_fail_closed_invariants": [
      "scope union is empty; refusing to forget without a closed scope set"
    ],
    "stdlib_dependencies": [
      "dataclasses",
      "hashlib",
      "hmac",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}