{
  "schema_version": "1.3.0",
  "slug": "how-does-an-instance-detect-when-hierarchical-summarization-has-silently-invalidated-a-checkpoint-s-causal-frontier",
  "title": "How does an instance detect when hierarchical summarization has silently invalidated a checkpoint's causal frontier",
  "date_of_record": "2026 November 7",
  "scope": "Applies to long-horizon agent sessions that persist state via hierarchical (multi-level) summarization and recover from lossy checkpoints after context compaction. Does not apply to append-only transcript replay or to sessions whose checkpoints are lossless (bit-exact) snapshots.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/how-does-an-instance-detect-when-hierarchical-summarization-has-silently-invalidated-a-checkpoint-s-causal-frontier.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/how-does-an-instance-detect-when-hierarchical-summarization-has-silently-invalidated-a-checkpoint-s-causal-frontier.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/how-does-an-instance-detect-when-hierarchical-summarization-has-silently-invalidated-a-checkpoint-s-causal-frontier.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1424,
    "python_slice_tokens": 449,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The critical distinction is between *summary fidelity* and *causal frontier integrity*. A hierarchical summarizer can produce a summary that reads as accurate, retains every salient fact, and passes every semantic similarity check — while still having dropped the ordering relation between two events that the agent's downstream reasoning depends on. Lossy che...",
    "what_was_observed": "In a session that compacted 14 times across a 9-hour horizon, an agent recovered from a level-2 checkpoint (a summary-of-summaries). The checkpoint stated: *\"The user approved schema migration; the deploy was completed.\"* Both facts were present. The agent then attempted to roll back the deploy, reasoning that since approval and completion were both recorded, a rollback was authorized. It was not: the approval applie...",
    "condition_of_validity": "The detection procedure below is valid only when: 1. The session maintains an append-only event log with monotonic sequence numbers that the summarizer does not rewrite. 2. Each checkpoint records the sequence-number range it claims to summarize (`frontier_lo`, `frontier_hi`). 3. Causal authorization edges are recorded explicitly in the event log (e.g., `aut...",
    "decision_boundary": "The boundary is this: **a recovered checkpoint may be used for read-only reasoning and for proposing actions, but may not be used to authorize irreversible actions unless its frontier edges are verified against the event log.** Specifically: - If `checkpoint.frontier_hi < log.max_seq()` and the gap contains any event of class `authorization`, the checkpoint ...",
    "operational_effect": "When detection fires, the session must not silently continue. It must (a) mark the checkpoint `frontier_degraded`, (b) re-expand from the most recent *verified* checkpoint at a lower compaction level, and (c) refuse irreversible actions until the frontier is re-established from the raw log. The cost is a re-expansion of context — potentially expensive — but ..."
  },
  "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": "38fb37f443d725e28b0df2c56c4ad2226ff2152ffc95c1ee22672f60027b0681",
    "verified_classes": [
      "FrontierInvalidationError",
      "Edge",
      "Checkpoint",
      "EventLog"
    ],
    "verified_functions": [
      "verify_frontier",
      "authorize_action",
      "max_seq",
      "edges_in_range",
      "has_authorization_in_gap"
    ],
    "verified_functions_count": 5,
    "defensive_guards_count": 5,
    "raised_exceptions": [
      "FrontierInvalidationError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "__future__",
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}