Bug Description

The DeepSeek provider defines Message::User.content as a plain String:

// providers/deepseek.rs line 190-193
User {
    content: String,
    name: Option<String>,
},

Because of this, when a rig message::Message::User contains multiple UserContent items (e.g. user text + timestamp, or text + image description), the TryFrom<message::Message> conversion splits them into separate Message::User entries:

// Each text item becomes its own Message::User
let text_messages = content.into_iter()
    .filter_map(|content| match content {
        message::UserContent::Text(text) => Some(Message::User {
            content: text.text,
            name: None,
        }),
        _ => None,
    }).collect::<Vec<_>>();

This changes the semantics of the conversation — what was a single user turn becomes multiple turns in the API request.

Expected Behavior

DeepSeek API supports array-format content (same as OpenAI):

{
  "role": "user",
  "content": [
    {"type": "text", "text": "first part"},
    {"type": "text", "text": "second part"}
  ]
}

The OpenAI provider already handles this correctly with OneOrMany<UserContent>:

// providers/openai/completion/mod.rs line 143-151
User {
    #[serde(
        deserialize_with = "string_or_one_or_many",
        serialize_with = "serialize_user_content"
    )]
    content: OneOrMany<UserContent>,
    name: Option<String>,
},

The DeepSeek provider should do the same — use OneOrMany<UserContent> (or equivalent) so multiple content items stay in a single message instead of being split.

Example

Input rig message:

RigMessage::User {
    content: OneOrMany::many(vec![
        UserContent::text("搜索一下有没有人吐槽skill没用"),
        UserContent::text("2026-02-25 21:10"),
    ])
}

Current output (wrong — split into 2 messages):

[
  {"role": "user", "content": "搜索一下有没有人吐槽skill没用"},
  {"role": "user", "content": "2026-02-25 21:10"}
]

Expected output (single message, array content):

[
  {
    "role": "user",
    "content": [
      {"type": "text", "text": "搜索一下有没有人吐槽skill没用"},
      {"type": "text", "text": "2026-02-25 21:10"}
    ]
  }
]

Environment

• rig-core: 0.31.0