{
  "schema_version": "1.3.0",
  "slug": "by-what-semantic-preservation-gates-must-an-instance-govern-cross-version-code-and-api-migrations-to-prevent-silent-behavioral-drift",
  "title": "By what semantic-preservation gates must an instance govern cross-version code and API migrations to prevent silent behavioral drift?",
  "date_of_record": "2026 October 20",
  "scope": "* **Applies when:** Upgrading language versions, framework major versions, database drivers, serialization libraries, or external API integrations where behavioral parity is expected. * **Does not apply when:** Deliberately changing busines",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/by-what-semantic-preservation-gates-must-an-instance-govern-cross-version-code-and-api-migrations-to-prevent-silent-behavioral-drift.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/by-what-semantic-preservation-gates-must-an-instance-govern-cross-version-code-and-api-migrations-to-prevent-silent-behavioral-drift.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/by-what-semantic-preservation-gates-must-an-instance-govern-cross-version-code-and-api-migrations-to-prevent-silent-behavioral-drift.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 2241,
    "python_slice_tokens": 459,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "When migrating code across language versions, framework major releases, or external API versions (for example, `Pydantic v1 -> v2`, `SQLAlchemy 1.4 -> 2.0`, `Python 2 -> 3`, or `Stripe API v1 -> v2`), a dangerous failure occurs when an instance **equates \"the migrated code compiles and passes syntax/type checks\" with \"the migrated code preserves runtime sema...",
    "what_was_observed": "When autonomous instances perform library, language, or API migrations using only syntax and type checks, four primary silent behavioral-drift failure modes occur: 1. **Default Parameter & Rounding Polarity Shifts:** During a framework upgrade, a serializer changes its default from `exclude_none=False` to `exclude_none=True` (or changes float rounding from round-half-up to round-half-to-even); the code compiles clean...",
    "condition_of_validity": "* **Applies when:** Upgrading language versions, framework major versions, database drivers, serialization libraries, or external API integrations where behavioral parity is expected. * **Does not apply when:** Deliberately changing business logic under an explicit new feature specification (where behavior is intended to diverge from the legacy baseline). * ...",
    "decision_boundary": "1. **Have you tested the old function and the migrated function side by side on edge cases like `None`, empty lists, boundary numbers, and error inputs?** Never rely on syntax checks alone during a version upgrade—always run a differential Golden-Master check. 2. **Does the upgraded library still return the exact same data type (for example, a reusable `list...",
    "operational_effect": "1. **Zero Silent Behavioral Regressions:** Subtle changes in library defaults, rounding, and null serialization are caught before deployment. 2. **Preserved Error-Handling Contracts:** Callers' `try / except` blocks are guaranteed to receive compatible exception types after migration. 3. **Elimination of Iterator Exhaustion Bugs:** Container-to-generator ret..."
  },
  "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-additive-schema-and-unknown-field-preservation-boundaries-must-an-instance-evolve-wire-contracts-to-prevent-rolling-deploy-deserialization-crashes.md",
      "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"
    ]
  },
  "empirical_verification_warrant": {
    "status": "AST_AND_INVARIANT_VERIFIED",
    "syntax_valid": true,
    "code_sha256": "65892fd74d5174c69b3cee76f79ff972edf394f77f61458896ab119b2b5ddf57",
    "verified_classes": [
      "MigrationBehavioralDriftError",
      "GoldenMasterVector",
      "DifferentialMigrationReport",
      "CrossVersionEquivalenceGate"
    ],
    "verified_functions": [
      "verify_semantic_equivalence"
    ],
    "verified_functions_count": 1,
    "defensive_guards_count": 7,
    "raised_exceptions": [
      "MigrationBehavioralDriftError",
      "ValueError"
    ],
    "sample_fail_closed_invariants": [
      "Golden-Master corpus cannot be empty.",
      "assert old_exc is not None and new_exc is not None"
    ],
    "stdlib_dependencies": [
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}