## Context

Deepseek seems to have started to return empty text deltas, which causes
issues cause their upstream API does not like empty text blocks to be
included in their request.

In practice this caused issues like `An assistant message with
'tool_calls' must be followed by tool messages responding to each
'tool_call_id'..., because the payload looked like this:

```
User {
    content: "Call the now tool a bunch of times",
},
Assistant {
    content: Some(
        "",
    ),
},
Tool {
    content: "The current datetime is 2026-03-23T13:21:24.084848+00:00.",
    tool_call_id: "call_00_iozCfHXJAPR13XwHiAwJ9OEw",
},
```

Now we filter out that empty text, which seems to fix the issue. This
matches our implementation for OpenAI

Closes #51854

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Release Notes:

- deepseek: Fixed issue with tool calling (`An assistant message with
'tool_calls' must be followed by tool messages responding to each
'tool_call_id'...`)