{
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    ],
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    [
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  ],
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      ],
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      "trace": [
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          "value": null,
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        },
        {
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          "previous_seq": 3,
          "drop": true,
          "reason": "hidden_by_previous_version_visible_to_all_allowed_snapshots"
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      ]
    },
    {
      "older_level_has_a": false,
      "oldest": 4,
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      "trace": [
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          "key": "a",
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      ]
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      "older_level_has_a": false,
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      "trace": [
        {
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      ],
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        {
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      ],
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        {
          "key": "a",
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          "value": null,
          "previous_seq": 101,
          "drop": false,
          "reason": "retain_version_or_tombstone"
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      "older_level_has_a": true,
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      ],
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        {
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        {
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        {
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          "previous_seq": 3,
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          "reason": "hidden_by_previous_version_visible_to_all_allowed_snapshots"
        }
      ]
    },
    {
      "older_level_has_a": true,
      "oldest": 5,
      "kept": [
        [
          "a",
          3,
          null
        ]
      ],
      "trace": [
        {
          "key": "a",
          "seq": 3,
          "value": null,
          "previous_seq": 101,
          "drop": false,
          "reason": "retain_version_or_tombstone"
        },
        {
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          "drop": true,
          "reason": "hidden_by_previous_version_visible_to_all_allowed_snapshots"
        }
      ]
    }
  ],
  "partial_snapshot_oracles": 42,
  "invalid_cases_rejected": [
    "duplicate_key_seq",
    "unsorted",
    "negative_seq",
    "bool_snapshot",
    "unknown_older_flag",
    "over_budget"
  ],
  "scope": "own bounded in-memory key/seq visibility model; None means logical absent/deleted only, not physical erasure; no LevelDB/SSTable/durability/privacy/IO/performance or Opera architecture claim"
}