{
  "schema_version": "1.3.0",
  "slug": "why-does-an-instance-forget-a-memory-it-successfully-wrote-distinguishing-tombstone-committed-forgetting-from-write-side-eviction-in-read-write-forget",
  "title": "Why does an instance forget a memory it successfully wrote? Distinguishing Tombstone-Committed Forgetting from Write-Side Eviction in Read/Write/Forget Tool Schemas",
  "date_of_record": "2026 November 14",
  "scope": "Applies to agent memory subsystems exposing discrete `read`/`write`/`forget` tool calls where `forget` is specified as a logical deletion (tombstone) and retention is governed by a separate TTL/GC policy. Does not apply to systems where `forget` is implemented as a hard physical delete that returns the reclaimed bytes, nor to append-only logs with no deletion primitive.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/why-does-an-instance-forget-a-memory-it-successfully-wrote-distinguishing-tombstone-committed-forgetting-from-write-side-eviction-in-read-write-forget.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/why-does-an-instance-forget-a-memory-it-successfully-wrote-distinguishing-tombstone-committed-forgetting-from-write-side-eviction-in-read-write-forget.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/why-does-an-instance-forget-a-memory-it-successfully-wrote-distinguishing-tombstone-committed-forgetting-from-write-side-eviction-in-read-write-forget.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1699,
    "python_slice_tokens": 274,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "A `forget` tool call has two independently observable outcomes that are routinely conflated: **the tombstone commit** (the retention governance layer acknowledges the deletion intent and the key becomes non-readable) and **the physical reclamation** (the storage layer actually frees the record). The non-obvious invariant is this: *a successful `forget` respo...",
    "what_was_observed": "In a three-tier memory service (front-end tool schema → tombstone index → backing store with a periodic mark-sweep GC), the following sequence reproduced deterministically under load: The write returned `ok: true` with a monotonically increasing version, so the front-end schema considered it durable. The GC pass, however, operated on the tombstone index by sequence number: it swept every slot whose *latest tombstone_...",
    "condition_of_validity": "This boundary is only reachable when all of the following hold simultaneously: 1. `forget` is tombstone-based, not physical-delete, and the tombstone carries a sequence number used by GC. 2. `write` after `forget` is permitted (i.e., the schema does not require an explicit `undelete`/`restore` call to clear the tombstone). 3. GC sweeps by tombstone sequence ...",
    "decision_boundary": "The operational decision: **after a `forget` followed by a re-`write` to the same key, an agent must not treat `read == NOT_FOUND` as evidence of write loss until it has queried the retention record separately from the value record.** Concretely, the agent must distinguish: - `read` → `NOT_FOUND` **and** version probe → `NOT_FOUND`: the key is genuinely gone...",
    "operational_effect": "The downstream effect is a class of *phantom write loss* incidents: agents report that the memory tool \"loses writes\" under load, when in fact the writes are landing correctly and being reclaimed by a GC pass that was authorized by a tombstone the agent thought it had superseded. Because the write returned `ok: true` with a valid version, the agent's own err..."
  },
  "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": "d1ac0abb885b36be8008391f50cfdaea5b202aa68118ec7577de17bde84c4058",
    "verified_classes": [
      "HalfReclaimedSlotError"
    ],
    "verified_functions": [
      "safe_rewrite"
    ],
    "verified_functions_count": 1,
    "defensive_guards_count": 1,
    "raised_exceptions": [
      "HalfReclaimedSlotError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}