fix(provider): only send tool_stream for Z.AI providers in streaming path (zeroclaw-labs#5806)

Squashed commits:

* a639203 fix(provider): only send tool_stream for Z.AI providers in streaming path

  The streaming method stream_chat_with_tools unconditionally set
  tool_stream: true for all providers when streaming was enabled.
  This caused 400 Bad Request errors on non-Z.AI OpenAI-compatible
  endpoints (e.g. litellm proxies) that reject the unrecognized
  tool_stream key.

  The non-streaming path already correctly used tool_stream_for_tools()
  which gates on requires_tool_stream() (Z.AI host or name check).
  Apply the same guard to both streaming payload branches so the field
  is only serialized for Z.AI providers.

  Related: zeroclaw-labs#2901

Author: zavertiaev

crates/zeroclaw-providers/src/compatible.rs

@@ -2195,7 +2195,11 @@ impl Provider for OpenAiCompatibleProvider {
                 messages: Self::convert_messages_for_native(&effective_messages, !merge),
                 temperature,
                 reasoning_effort: self.reasoning_effort.clone(),
-                tool_stream: if options.enabled { Some(true) } else { None },
+                tool_stream: if options.enabled {
+                    self.tool_stream_for_tools(true)
+                } else {
+                    None
+                },
                 stream: Some(options.enabled),
                 tools: tools.clone(),
                 tool_choice: tools.as_ref().map(|_| "auto".to_string()),
@@ -2215,7 +2219,11 @@ impl Provider for OpenAiCompatibleProvider {
                 messages,
                 temperature,
                 reasoning_effort: self.reasoning_effort.clone(),
-                tool_stream: if options.enabled { Some(true) } else { None },
+                tool_stream: if options.enabled {
+                    self.tool_stream_for_tools(false)
+                } else {
+                    None
+                },
                 stream: Some(options.enabled),
                 tools: None,
                 tool_choice: None,
@@ -3597,6 +3605,14 @@ mod tests {
         assert!(!json.contains("\"tool_stream\""));
     }
 
+    #[test]
+    fn non_zai_provider_omits_tool_stream_regardless_of_streaming() {
+        let provider = make_provider("custom", "https://proxy.example.com/v1", None);
+        // tool_stream_for_tools should return None for non-Z.AI providers
+        assert_eq!(provider.tool_stream_for_tools(true), None);
+        assert_eq!(provider.tool_stream_for_tools(false), None);
+    }
+
     #[test]
     fn z_ai_host_enables_tool_stream_for_custom_profiles() {
         let provider = make_provider("custom", "https://api.z.ai/api/coding/paas/v4", None);