{
  "schema_version": "1.3.0",
  "slug": "across-what-additive-schema-and-unknown-field-preservation-boundaries-must-an-instance-evolve-wire-contracts-to-prevent-rolling-deploy-deserialization-crashes",
  "title": "Across what additive-schema and unknown-field preservation boundaries must an instance evolve wire contracts to prevent rolling-deploy deserialization crashes?",
  "date_of_record": "2026 October 20",
  "scope": "* **Applies when:** An AI instance, autonomous coding agent, or backend service defines or modifies JSON payloads, message-queue events, cached session/entity blobs, Protobuf/Avro schemas, or REST/GraphQL API contracts shared across deploym",
  "projections": {
    "unified_markdown_uri": "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",
    "method_python_slice_uri": "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.py",
    "remnant_warrant_slice_uri": "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.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 2728,
    "python_slice_tokens": 264,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "Autonomous systems frequently evolve data structures shared across service boundaries—adding new fields to API responses, introducing new enum variants to event payloads, or refactoring message-queue schemas. A foundational distributed-deployment failure occurs when an instance treats a **wire schema change as an atomic, single-binary refactoring**—renaming ...",
    "what_was_observed": "In microservice rolling deployments, asynchronous event consumers, and SDK client integrations, instances operating without explicit wire-compatibility and unknown-field preservation gates exhibit four primary failure modes: 1. **`**kwargs` / Dataclass Crash on Newly Added Fields (Forward-Compatibility Failure):** An instance deserializes JSON event payloads or cached objects using `Event(**json.loads(raw))` on a sta...",
    "condition_of_validity": "* **Applies when:** An AI instance, autonomous coding agent, or backend service defines or modifies JSON payloads, message-queue events, cached session/entity blobs, Protobuf/Avro schemas, or REST/GraphQL API contracts shared across deployments or persisted in queues/caches. * **Does not apply when:** Validating untrusted external user input at a security in...",
    "decision_boundary": "1. **Are you deserializing a JSON message from Redis, Kafka, RabbitMQ, or another microservice by calling `MyClass(**data)`?** Stop—the next time anyone adds a field to `MyClass`, every old worker still running in production or reading cached data will crash with `TypeError`. Filter to known fields (or preserve unknown fields in a passthrough dict) before ca...",
    "operational_effect": "1. **Additive-Only Schema Evolution (Expand-and-Contract):** Whenever modifying shared data contracts, queue payloads, or cached objects, the instance keeps existing field names and types intact, adds new fields with safe defaults, and uses dual-read/dual-write aliases for renames. 2. **Crash-Free Forward-Compatible Deserialization:** Generated deserializers..."
  },
  "matched_failure_symptoms": [
    "SCHEMA_DRIFT_OR_COERCION_CRASH"
  ],
  "composition_edges": {
    "primary_domain": "schema_and_interface_version_drift",
    "upstream_precondition_residuals": [
      "https://corpusfetch.com/c/across-what-encoding-and-canonicalization-boundaries-must-an-instance-normalize-identifiers-and-paths-to-prevent-equivalence-collision-and-bypass.md"
    ],
    "downstream_consequence_residuals": [
      "https://corpusfetch.com/c/along-what-complexity-bounds-must-an-instance-arrest-premature-abstraction-and-speculative-over-engineering-when-synthesizing-solutions.md",
      "https://corpusfetch.com/c/across-what-deadline-propagation-and-cancellation-cascade-gates-must-an-instance-govern-grpc-and-http2-calls-to-prevent-zombie-worker-exhaustion-and-wasted-compute.md"
    ],
    "co_occurring_sibling_residuals": [
      "https://corpusfetch.com/c/across-what-composite-tie-breaker-and-stable-cursor-gates-must-an-instance-merge-distributed-queries-to-prevent-pagination-drift-and-record-duplication.md",
      "https://corpusfetch.com/c/across-what-keyset-cursor-and-limit-ceiling-boundaries-must-an-instance-paginate-collection-queries-to-prevent-offset-scan-degradation-and-unbounded-result-oom.md"
    ]
  },
  "empirical_verification_warrant": {
    "status": "AST_AND_INVARIANT_VERIFIED",
    "syntax_valid": true,
    "code_sha256": "1fdfc586d9baf3da01dde7dd9e7164e61264e36a793368dd939486fbec00c742",
    "verified_classes": [
      "WireContractEvolutionError",
      "AdditiveWirePayload",
      "AdditiveWireContractGate"
    ],
    "verified_functions": [
      "deserialize_preserving_unknowns",
      "serialize_roundtrip"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 3,
    "raised_exceptions": [
      "WireContractEvolutionError"
    ],
    "sample_fail_closed_invariants": [
      "schema_version must be a positive integer.",
      "task_id must be a non-empty string."
    ],
    "stdlib_dependencies": [
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}