fix: retry without tools when OpenAI-compatible server returns empty response

[thanhnnict]

Problem

Some OpenAI-compatible servers (NIM, vLLM, TGI) return content: null with an empty tool_calls: [] array when tools are provided in the request but the model decides not to call any tool. This results in blank responses rendered in the Continue GUI.

Solution

Detect empty response (content: null + tool_calls: []) and retry the same request without the tools parameter. The model then responds with text content normally.

Behavior Matrix

Model Response	tools in request	Retry?	Result
content: "Hello", tool_calls: []	Yes	❌ No	Text shown normally
content: null, tool_calls: [{...}]	Yes	❌ No	Tool call executed
content: null, tool_calls: []	Yes	✅ Yes	Retry → text shown
content: null, tool_calls: []	No	❌ No	Empty (no tools to remove)

Affected Models

• nvidia/nemotron-ultra-253b (NIM) — frequently
• deepseek-ai/DeepSeek-V4-Flash (vLLM) — occasionally
• Any OpenAI-compatible server with tool support

Trade-offs

• Latency: Adds one extra API call when empty response is detected (~2-5s)
• Correctness: Model genuinely wants to say nothing → forced to respond (acceptable for coding assistant)
• Scope: Only affects chatCompletionNonStream (non-streaming path)

Related

• Agent Mode: Streamed tool_calls from vLLM ignored - no action performed #5508

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