FeishuInboundMapper

Parses a decrypted Feishu Event Subscription v2 envelope into an InboundMessage.

Schema 2.0 envelope shape:

{
"schema": "2.0",
"header": {"event_id":"...","event_type":"im.message.receive_v1","tenant_key":"...", ...},
"event": {
"sender": {"sender_id":{"open_id":"...","user_id":"...","union_id":"..."}, "sender_type":"user"},
"message": {
"message_id":"om_...",
"chat_id":"oc_...",
"chat_type":"p2p|group",
"message_type":"text|...",
"content":"{\"text\":\"@_user_1 hello\"}"
}
}
}

Text messages (message_type=text) map to their content; the inner content field is a JSON-encoded string and is re-parsed to read the text field. Media messages (image / file / folder / audio / media) map to a neutral marker text plus the ChannelMediaMetadata contract: the image_key / file_key material identifiers and per-kind metadata are preserved verbatim, and fetching the bytes (a token-authenticated message-resource download) is left to the application. Other message types (post, sticker, interactive, share cards, ...) are returned as Optional#empty() so the caller can ack without dispatching.