[Bug] Feishu message.send appears to require card and plain text send fails, while a minimal card send succeeds

Summary

In a Feishu direct chat, trying to use the message tool for an explicit outbound text send did not work as expected.

Observed behavior:

1. Calling message.send with channel:"feishu" and a normal message:"..." payload failed local validation because card was treated as required.
2. Retrying with an empty card: {} passed tool validation but failed at runtime with HTTP 400.
3. Retrying again with a minimal valid Feishu card payload succeeded.

So in practice, explicit Feishu delivery worked via card send, but not via the expected plain text send path.

Environment

• OpenClaw version: 2026.3.23-2
• Channel: Feishu direct chat
• Surface under test: message tool
• Host: Linux gateway

Why I tested this

I was debugging another Feishu delivery issue where a parent reply after sessions_spawn completion sometimes was not visible to the user.

To isolate the delivery path, I tried bypassing the normal parent final-answer route and explicitly sending the result through the message tool.

That revealed a second issue: Feishu plain text explicit send did not work, while Feishu card send did.

Reproduction

Attempt 1: plain text only

Tool call shape:

{
  "action": "send",
  "channel": "feishu",
  "message": "test text"
}

Observed result:

• local tool validation failed
• error said card was required

Attempt 2: plain text + empty card

Tool call shape:

{
  "action": "send",
  "channel": "feishu",
  "message": "test text",
  "card": {}
}

Observed result:

• validation passed
• runtime returned HTTP 400

Attempt 3: minimal valid card

Tool call shape:

{
  "action": "send",
  "channel": "feishu",
  "card": {
    "config": { "wide_screen_mode": true },
    "header": {
      "title": {
        "tag": "plain_text",
        "content": "显式发送测试结果"
      }
    },
    "elements": [
      {
        "tag": "div",
        "text": {
          "tag": "lark_md",
          "content": "hello"
        }
      }
    ]
  }
}

Observed result:

• send succeeded
• user received the card

Expected behavior

At least one of these should be true:

1. message.send for Feishu should support plain text sends without requiring card, or
2. the schema / docs should clearly state that Feishu explicit sends through message.send require card payloads and plain text is unsupported.

Right now the behavior is confusing because the generic message tool strongly suggests text sends are normal, but Feishu appears to reject or mis-handle that path.

Actual behavior

• plain text send fails schema validation because card appears required
• adding an empty card just moves failure to runtime HTTP 400
• only a proper Feishu card succeeds

Suspected scope

Could be one or more of:

1. message tool schema incorrectly marks card as globally required instead of conditionally required
2. Feishu adapter expects a card payload even for cases where generic text send should be supported
3. Feishu adapter text-send path is broken or not wired for this tool surface
4. provider-specific validation / normalization for Feishu is inconsistent with the generic message API

Why this matters

This blocks a clean workaround for other Feishu delivery issues.

When normal assistant replies are suspect, the obvious fallback is explicit message.send text delivery. But if Feishu explicit text send also fails, users are forced into card-only workarounds.

Related context

This was discovered while debugging a separate issue already filed for:

• Feishu DM missing the parent final reply after sessions_spawn completion even though the reply exists in session history

That issue is about normal reply visibility. This issue is narrower: explicit Feishu text send via message.send appears broken or undocumented.

Request

Please clarify whether Feishu message.send is supposed to support plain text sends.

If yes, this looks like a bug. If no, please make the schema and docs reflect that clearly so callers know they must send cards instead.