agent: Allow customizing temperature by provider/model (#30033)

Adds a new `agent.model_parameters` setting that allows the user to
specify a custom temperature for a provider AND/OR model:

```json5
    "model_parameters": [
      // To set parameters for all requests to OpenAI models:
      {
        "provider": "openai",
        "temperature": 0.5
      },
      // To set parameters for all requests in general:
      {
        "temperature": 0
      },
      // To set parameters for a specific provider and model:
      {
        "provider": "zed.dev",
        "model": "claude-3-7-sonnet-latest",
        "temperature": 1.0
      }
    ],
```

Release Notes:

- agent: Allow customizing temperature by provider/model

---------

Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
Co-authored-by: Marshall Bowers <git@maxdeviant.com>

crates/agent/src/buffer_codegen.rs

@@ -2,6 +2,7 @@ use crate::context::ContextLoadResult;
 use crate::inline_prompt_editor::CodegenStatus;
 use crate::{context::load_context, context_store::ContextStore};
 use anyhow::Result;
+use assistant_settings::AssistantSettings;
 use client::telemetry::Telemetry;
 use collections::HashSet;
 use editor::{Anchor, AnchorRangeExt, MultiBuffer, MultiBufferSnapshot, ToOffset as _, ToPoint};
@@ -383,7 +384,7 @@ impl CodegenAlternative {
             if user_prompt.trim().to_lowercase() == "delete" {
                 async { Ok(LanguageModelTextStream::default()) }.boxed_local()
             } else {
-                let request = self.build_request(user_prompt, cx)?;
+                let request = self.build_request(&model, user_prompt, cx)?;
                 cx.spawn(async move |_, cx| model.stream_completion_text(request.await, &cx).await)
                     .boxed_local()
             };
@@ -393,6 +394,7 @@ impl CodegenAlternative {
 
     fn build_request(
         &self,
+        model: &Arc<dyn LanguageModel>,
         user_prompt: String,
         cx: &mut App,
     ) -> Result<Task<LanguageModelRequest>> {
@@ -441,6 +443,8 @@ impl CodegenAlternative {
             }
         });
 
+        let temperature = AssistantSettings::temperature_for_model(&model, cx);
+
         Ok(cx.spawn(async move |_cx| {
             let mut request_message = LanguageModelRequestMessage {
                 role: Role::User,
@@ -463,7 +467,7 @@ impl CodegenAlternative {
                 mode: None,
                 tools: Vec::new(),
                 stop: Vec::new(),
-                temperature: None,
+                temperature,
                 messages: vec![request_message],
             }
         }))