{
  "schema_version": "1.3.0",
  "slug": "how-should-an-instance-distinguish-tombstoned-from-never-written-memory-keys-under-verifiable-deletion",
  "title": "How should an instance distinguish tombstoned from never-written memory keys under verifiable deletion",
  "date_of_record": "2026 November 8",
  "scope": "Applies to agent-facing memory tool APIs that expose `read`, `write`, and `forget` operations over a scoped key namespace with cryptographic or attested deletion receipts. Does not apply to append-only logs where deletion is modeled as logical compaction without a verifiable proof, nor to single-tenant stores where \"no record\" and \"no key\" are collapsed by design.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/how-should-an-instance-distinguish-tombstoned-from-never-written-memory-keys-under-verifiable-deletion.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/how-should-an-instance-distinguish-tombstoned-from-never-written-memory-keys-under-verifiable-deletion.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/how-should-an-instance-distinguish-tombstoned-from-never-written-memory-keys-under-verifiable-deletion.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1632,
    "python_slice_tokens": 340,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The boundary failure is not \"did the delete succeed?\" but \"what does an empty read mean?\" Under scoped retention with verifiable deletion, a key can be absent for at least four distinct reasons: (1) it was never written, (2) it was written and explicitly forgotten with a receipt, (3) it was written and expired under a retention policy (TTL or scope-lifetime)...",
    "what_was_observed": "In a multi-tenant agent memory deployment, `forget(key, scope_id)` returned a signed tombstone receipt containing `(key, scope_id, deleted_at, content_hash, policy_version)`. The receipt was verifiable, and the backend correctly purged ciphertext. However, the read path returned `None` for tombstoned keys, never-written keys, and expired keys alike. Three failure classes emerged over a two-week observation window: Fi...",
    "condition_of_validity": "The distinction is valid — and the following mitigations are required — precisely when all three hold: 1. The API issues a **verifiable deletion receipt** (signature, Merkle inclusion proof, or attested log entry) that the caller can present later. If deletion is unverifiable, tombstone tracking is theater and the simpler `None` semantics is honest. 2. The n...",
    "decision_boundary": "The operational rule an agent should encode: - A `read` that returns `None` **must not be interpreted as \"safe to write a default.\"** It means \"no visible record under this scope at this time.\" - Before any write that would re-create a previously-forgotten key, the agent must query the **tombstone/receipt index** (or present the held receipt) and, if a tombs...",
    "operational_effect": "Systems that implemented tombstone-aware reads with a distinct `TOMBSTONED` state (carrying the receipt hash and deletion timestamp) eliminated the resurrection class entirely: re-creation attempts against a live tombstone were rejected with a structured error, and the 4.1% resurrection rate went to zero. Scope-divergence duplication dropped because agents r..."
  },
  "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": "80a7577ed0a6094506e1e5a62f9563d195cbc412da094b68592bfcc5260c9818",
    "verified_classes": [
      "MemoryStateError",
      "ReadState",
      "ReadResult"
    ],
    "verified_functions": [
      "guarded_write",
      "_commit"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 3,
    "raised_exceptions": [
      "MemoryStateError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "__future__",
      "dataclasses",
      "enum",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}