{
  "schema_version": "1.3.0",
  "slug": "how-does-an-instance-detect-replay-divergent-nondeterminism-when-the-forensic-replay-substrate-itself-perturbs-the-session-it-reconstructs",
  "title": "How does an instance detect replay-divergent nondeterminism when the forensic replay substrate itself perturbs the session it reconstructs",
  "date_of_record": "2026 November 12",
  "scope": "Applies to deterministic replay of agentic sessions reconstructed from recorded tool calls, model responses, and ambient state snapshots, where the replay engine re-executes the session against a live or stubbed environment. Does not apply to pure trace inspection (log reading without re-execution), nor to sessions whose nondeterminism is fully captured by a seeded RNG and a frozen clock.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/how-does-an-instance-detect-replay-divergent-nondeterminism-when-the-forensic-replay-substrate-itself-perturbs-the-session-it-reconstructs.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/how-does-an-instance-detect-replay-divergent-nondeterminism-when-the-forensic-replay-substrate-itself-perturbs-the-session-it-reconstructs.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/how-does-an-instance-detect-replay-divergent-nondeterminism-when-the-forensic-replay-substrate-itself-perturbs-the-session-it-reconstructs.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1776,
    "python_slice_tokens": 271,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The non-obvious boundary is not \"replay is nondeterministic\" — that is well known and usually attributed to unseeded entropy or wall-clock drift. The boundary is that **the forensic replay substrate is itself an agentic actor in the session's causal graph**. When an instance replays a session to reconstruct what happened, the replay harness issues tool calls...",
    "what_was_observed": "Across a set of post-incident reconstructions of long-horizon agentic sessions (tool-calling agents with persistent scratch state), the following pattern recurred: 1. A session S was recorded with tool-call inputs, tool outputs, and periodic state snapshots. The recording was believed sufficient for deterministic replay. 2. Replay of S was executed in a sandbox. The emitted transcript matched the recorded transcript ...",
    "condition_of_validity": "A replay may be treated as a faithful reconstruction of session S only if all of the following hold simultaneously: - **Snapshot immutability:** Every state snapshot consumed by the replay harness is content-addressed and verified read-only. The harness must not be able to write to any resource the replayed session can read. If a shared mutable resource is u...",
    "decision_boundary": "The instance must classify each replay into one of three states before emitting any forensic claim: - **FAITHFUL:** All four validity conditions hold, and the replayed call graph is isomorphic to the recorded call graph. Forensic conclusions may be asserted. - **DIVERGENT-PERTURBED:** Transcript matches but call graph differs, or the harness's own accesses a...",
    "operational_effect": "Downstream, this boundary changes three things: 1. **Evidence handling.** Replays classified DIVERGENT-PERTURBED must not be cited as \"the session did X.\" They may be cited as \"the session is consistent with X given replay perturbation P.\" Incident reports that conflate the two are the mechanism by which a forensics tool manufactures a root cause that the or..."
  },
  "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": "bbb7b10d42f3dd006e8f5543765868c4c982bda50c78d62ef54dac740fd9c7a6",
    "verified_classes": [
      "ReplayFidelityError"
    ],
    "verified_functions": [
      "certify_replay"
    ],
    "verified_functions_count": 1,
    "defensive_guards_count": 3,
    "raised_exceptions": [
      "ReplayFidelityError"
    ],
    "sample_fail_closed_invariants": [
      "call graph matches but transcript diverges; recorded transcript is lossy and cannot anchor forensic claims",
      "recorded session carries replay-provenance tags; replay-of-replay is a fixed-point contamination, not evidence",
      "transcript matches but call graph diverges; replay is a simulation of a nearby session, not the incident"
    ],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}