[
  {
    "name": "gossip-001-cross-node-propagation",
    "description": "An envelope published at node A is observed at node B after a single round of gossip. The envelope's SAID is identical at both observation points; the gossip layer does not modify the wire bytes.",
    "scenario": {
      "publisher": "node_A",
      "publish_frame": 184300,
      "envelope_said": "EBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB",
      "envelope_canonical_cbor_hex": "a6677665727369",
      "gossip_rounds": 1,
      "observers": ["node_B"]
    },
    "expected_observations": [
      {
        "observer": "node_B",
        "observed_said": "EBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB",
        "observation_frame": 184301,
        "outcome": "accepted"
      }
    ]
  },
  {
    "name": "gossip-002-said-conflict-rejected",
    "description": "Two different envelopes are gossiped under the same SAID. The receiving node MUST reject the second envelope. The SAID is content-addressed (BLAKE3 of the canonical CBOR); two structurally-different envelopes producing the same SAID is either a collision (cryptographically negligible) or an adversarial substitution attempt. Either way, the receiver keeps the first observation and rejects the second.",
    "scenario": {
      "publisher_a": "node_A",
      "publisher_b": "node_B",
      "publish_frame": 184310,
      "envelope_a_said": "ECCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC",
      "envelope_a_canonical_cbor_hex": "a6677665727369aaaa",
      "envelope_b_said": "ECCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC",
      "envelope_b_canonical_cbor_hex": "a6677665727369bbbb",
      "receiver": "node_C"
    },
    "expected_outcome": {
      "accepted": "envelope_a",
      "rejected": "envelope_b",
      "rejection_reason": "said_collision_envelope_a_already_observed",
      "alert_class": "potential_substitution_attack"
    }
  },
  {
    "name": "gossip-003-sequence-gap-detection",
    "description": "An envelope arrives at node B referencing a previous-history-hash that node B has not seen. Node B MUST detect the gap, request the missing history via gossip backfill, and not commit the envelope's transition until the gap is closed. The expected behaviour is *not* to reject the envelope — it is to defer acceptance pending backfill.",
    "scenario": {
      "publisher": "node_A",
      "publish_frame": 184320,
      "envelope_said": "EDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD",
      "envelope_previous_history_hash": "EFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF",
      "receiver": "node_B",
      "receiver_known_history_heads": [
        "EAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
        "EBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB"
      ]
    },
    "expected_outcome": {
      "observer": "node_B",
      "outcome": "deferred_pending_backfill",
      "missing_history_hash": "EFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF",
      "backfill_request_targets": ["node_A"],
      "backfill_max_frames": 256,
      "alert_class": "history_gap_detected"
    }
  }
]