{
  "schema_version": "1.3.0",
  "slug": "what-structural-signals-indicate-lossy-compaction-has-crossed-the-rehydration-boundary",
  "title": "What structural signals indicate lossy compaction has crossed the rehydration boundary",
  "date_of_record": "2026 November 12",
  "scope": "Applies to agentic systems that compact conversation/working context via lossy summarization while relying on an external retrieval store to rehydrate evicted spans on demand. Does not apply to lossless compaction (deduplication, verbatim windowing, pointer-only references) where the summary is a faithful index rather than a semantic projection.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-lossy-compaction-has-crossed-the-rehydration-boundary.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-lossy-compaction-has-crossed-the-rehydration-boundary.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-lossy-compaction-has-crossed-the-rehydration-boundary.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1584,
    "python_slice_tokens": 267,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The failure is not \"the summary lost information.\" Every lossy summary loses information by construction; that is the contract. The failure is that the summary *retains a confident surface form for a fact whose retrievability has silently degraded below the threshold needed to reconstruct it*. The compaction step and the rehydration step each succeed locally...",
    "what_was_observed": "In a long-running agent session (≈140 turns), a compaction pass summarized a prior span as: *\"User confirmed the migration window is Thursday and that rollback is not required.\"* The source span actually read: *\"Let's pencil in Thursday for the migration, but I want a rollback path ready — don't treat it as optional.\"* The summary inverted a negation (`not required` vs. `don't treat it as optional`) and dropped the c...",
    "condition_of_validity": "The rehydration boundary is only trustworthy when all of the following hold at the moment a summary claim is *used*, not merely when it was written: - The summary text contains a derivable key (verbatim anchor, entity + attribute pair, or stable ID) for every non-self-sufficient claim. - The retrieval backend distinguishes \"key absent\" from \"key present but ...",
    "decision_boundary": "The operative rule: **treat a summary claim as self-sufficient only if it passes a polarity-and-quantifier-preserving check against its source span; otherwise force a rehydration attempt before the claim can influence an irreversible action.** Concretely, before any action with side effects (writes, deletions, external calls, state transitions), the agent mu...",
    "operational_effect": "Systems that enforce the joint invariant observe a specific signature: rehydration calls cluster immediately before irreversible actions, and tombstoned-key errors surface as *blocking* rather than *silent*. The cost is a modest latency bump at action boundaries. The benefit is that polarity inversions and dropped conditionals — the failure class that LLM fa..."
  },
  "matched_failure_symptoms": [
    "CONTEXT_DRIFT_OR_ATTENTION_DILUTION"
  ],
  "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": "9b7577ed25535d4803200d17894757a35db7af02bbe51150c1a67456ad08f63a",
    "verified_classes": [
      "RehydrationBoundaryError"
    ],
    "verified_functions": [
      "assert_claim_substantiated",
      "pre_action_gate"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 4,
    "raised_exceptions": [
      "RehydrationBoundaryError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}