{
  "schema_version": "1.3.0",
  "slug": "what-invariants-must-survive-when-a-tools-schema-changes-silently-between-tool-versions",
  "title": "What invariants must survive when a tool's schema changes silently between tool versions?",
  "date_of_record": "2026 October 20",
  "scope": "* **Applies when:** The tool's schema can change silently, the agent relies on schema semantics, and downstream consequences of drift are material. * **Does not apply when:** The tool's schema is content-addressed or immutable, or the agent",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-invariants-must-survive-when-a-tools-schema-changes-silently-between-tool-versions.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-invariants-must-survive-when-a-tools-schema-changes-silently-between-tool-versions.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-invariants-must-survive-when-a-tools-schema-changes-silently-between-tool-versions.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1004,
    "python_slice_tokens": 256,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The separation between **tool identity** (the name and nominal version) and **tool schema fingerprint** (the exact input/output structure and semantics). Relying on identity alone creates the **Schema Drift Blindness**: the agent invokes a tool at version \"v2,\" the tool's behavior has silently changed (a field renamed, a type changed, a default altered), and...",
    "what_was_observed": "In tool-invoking agent architectures, failing to verify schema fingerprints produces three primary failure modes: 1. **Silent Field Rename:** A field `user_id` is renamed to `userId` in a minor version. The agent's integration sends `user_id`, the tool ignores it silently, and the tool executes with default values. 2. **Type Coercion Ambiguity:** A numeric field changes from `string` to `integer` in an undocumented u...",
    "condition_of_validity": "* **Applies when:** The tool's schema can change silently, the agent relies on schema semantics, and downstream consequences of drift are material. * **Does not apply when:** The tool's schema is content-addressed or immutable, or the agent uses only the tool's minimum surface where drift is impossible.",
    "decision_boundary": "1. **Has the tool's schema fingerprint been recorded?** If no, the agent has no baseline. It must capture the fingerprint on next invocation. 2. **Does the current schema fingerprint match the recorded baseline?** If yes, standard invocation applies. If no, proceed to drift handling. 3. **Does the drift affect required fields, types, or defaults used by the ...",
    "operational_effect": "1. **Silent Breakage Prevention:** Catches schema drift before downstream behavior diverges. 2. **Migration Automation:** Provides executable migration predicates, allowing the agent to adapt without human intervention. 3. **Cross-Version Compatibility:** Enables the agent to operate across tool versions by verifying only the surface it uses."
  },
  "matched_failure_symptoms": [
    "SCHEMA_DRIFT_OR_COERCION_CRASH"
  ],
  "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": "5c012c360bed6129a5ca740f8d56e1a3a4e8accba52d027f0c6f604171163133",
    "verified_classes": [
      "SchemaVerdict",
      "ToolSchema",
      "SchemaBaseline",
      "SchemaManifest",
      "ToolSchemaDriftGuard"
    ],
    "verified_functions": [
      "_hash",
      "evaluate_schema"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 0,
    "raised_exceptions": [],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "enum",
      "hashlib",
      "json"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}