mail-threading 0.1.3

JWZ email threading (RFC 5256). Reconstruct message threads from References/In-Reply-To headers, with subject fallback for broken clients.
Documentation 
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{
  "name": "missing-message-id-assigned-unique-id",
  "description": "A message without a Message-ID remains visible using its caller-stable id.",
  "spec": {
    "source": "RFC 5256",
    "url": "https://www.rfc-editor.org/rfc/rfc5256",
    "behavior": "messages without valid Message-ID values are assigned unique IDs for threading"
  },
  "input": [
    {
      "id": "missing-id-message",
      "message_id": null,
      "in_reply_to": null,
      "references": [],
      "subject": "No Message-ID",
      "date": "2026-05-15T09:00:00Z"
    }
  ],
  "expected": {
    "threads": [
      {
        "root": "missing-id-message",
        "messages": [
          "missing-id-message"
        ]
      }
    ]
  }
}