{
  "schema_version": "1.3.0",
  "slug": "what-communication-invariants-must-survive-when-agents-speak-different-protocol-versions",
  "title": "What communication invariants must survive when agents speak different protocol versions?",
  "date_of_record": "2026 October 20",
  "scope": "* **Applies when:** The protocol has multiple active versions in the wild, the message format parses across versions, but the semantics or constraints have changed. * **Does not apply when:** All agents use the same protocol version, or the",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-communication-invariants-must-survive-when-agents-speak-different-protocol-versions.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-communication-invariants-must-survive-when-agents-speak-different-protocol-versions.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-communication-invariants-must-survive-when-agents-speak-different-protocol-versions.warrant.json"
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  "remnant_summary": {
    "core_distinction": "The separation between **syntactic compatibility** (the message parses in both versions, e.g., JSON field names overlap) and **semantic compatibility** (the fields mean the same thing, have the same constraints, and produce the same downstream behavior). Relying on syntax creates the **Version Semantic Drift**: the message parses, but a field that meant \"pri...",
    "what_was_observed": "In multi-version agent protocols, failing to preserve semantic invariants produces three primary failure modes: 1. **Field Semantic Shift:** A field named `status` changes from an enum (`active`, `inactive`) in v1 to a free-form string in v2. The v1 agent sends `active`, the v2 agent interprets it as arbitrary text and processes downstream differently. 2. **Required Field Addition:** V2 requires a new field `tenant_i...",
    "condition_of_validity": "* **Applies when:** The protocol has multiple active versions in the wild, the message format parses across versions, but the semantics or constraints have changed. * **Does not apply when:** All agents use the same protocol version, or the protocol evolution is strictly backward-compatible by design (e.g., adding optional fields only).",
    "decision_boundary": "1. **Are both agents using the same protocol version?** If yes, standard processing applies. If no, proceed. 2. **Do the agents have a shared `field_semantic_registry` and `compatibility_profile_hash`?** If no, semantic drift cannot be detected. The receiver must reject the message. 3. **Do any fields exhibit `field_constraint_delta` (required, type, or size...",
    "operational_effect": "1. **Semantic Drift Detection:** Prevents silent misinterpretation of fields with changed meaning across versions. 2. **Constraint Enforcement:** Rejects messages that would violate the receiving version's constraints, preventing data loss or corruption. 3. **Deterministic Interop:** Provides a clear compatibility profile for cross-version communication, eli..."
  },
  "matched_failure_symptoms": [
    "DOMAIN:EPISTEMIC_PROVENANCE_AND_FEDERATION_ROUTING"
  ],
  "composition_edges": {
    "primary_domain": "epistemic_provenance_and_federation_routing",
    "upstream_precondition_residuals": [
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      "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"
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    "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"
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  },
  "empirical_verification_warrant": {
    "status": "AST_AND_INVARIANT_VERIFIED",
    "syntax_valid": true,
    "code_sha256": "834dcd2cf221eaa2d1a8bf3750f3c2dd1b3c09e52ddb8ba0a779947b6122e76b",
    "verified_classes": [
      "ProtocolCompatVerdict",
      "VersionPair",
      "FieldDelta",
      "CompatibilityProfile",
      "CompatManifest",
      "ProtocolVersionGuard"
    ],
    "verified_functions": [
      "_hash",
      "evaluate_compatibility"
    ],
    "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
  }
}