chore: introduce ModelFamily abstraction (#1838)

To date, we have a number of hardcoded OpenAI model slug checks spread
throughout the codebase, which makes it hard to audit the various
special cases for each model. To mitigate this issue, this PR introduces
the idea of a `ModelFamily` that has fields to represent the existing
special cases, such as `supports_reasoning_summaries` and
`uses_local_shell_tool`.

There is a `find_family_for_model()` function that maps the raw model
slug to a `ModelFamily`. This function hardcodes all the knowledge about
the special attributes for each model. This PR then replaces the
hardcoded model name checks with checks against a `ModelFamily`.

Note `ModelFamily` is now available as `Config::model_family`. We should
ultimately remove `Config::model` in favor of
`Config::model_family::slug`.

codex-rs/core/src/openai_tools.rs

@@ -1,9 +1,9 @@
 use serde::Serialize;
 use serde_json::json;
 use std::collections::BTreeMap;
-use std::sync::LazyLock;
 
 use crate::client_common::Prompt;
+use crate::model_family::ModelFamily;
 use crate::plan_tool::PLAN_TOOL;
 
 #[derive(Debug, Clone, Serialize)]
@@ -42,8 +42,7 @@ pub(crate) enum JsonSchema {
     },
 }
 
-/// Tool usage specification
-static DEFAULT_TOOLS: LazyLock<Vec<OpenAiTool>> = LazyLock::new(|| {
+fn create_shell_tool() -> OpenAiTool {
     let mut properties = BTreeMap::new();
     properties.insert(
         "command".to_string(),
@@ -54,7 +53,7 @@ static DEFAULT_TOOLS: LazyLock<Vec<OpenAiTool>> = LazyLock::new(|| {
     properties.insert("workdir".to_string(), JsonSchema::String);
     properties.insert("timeout".to_string(), JsonSchema::Number);
 
-    vec![OpenAiTool::Function(ResponsesApiTool {
+    OpenAiTool::Function(ResponsesApiTool {
         name: "shell",
         description: "Runs a shell command, and returns its output.",
         strict: false,
@@ -63,29 +62,26 @@ static DEFAULT_TOOLS: LazyLock<Vec<OpenAiTool>> = LazyLock::new(|| {
             required: &["command"],
             additional_properties: false,
         },
-    })]
-});
-
-static DEFAULT_CODEX_MODEL_TOOLS: LazyLock<Vec<OpenAiTool>> =
-    LazyLock::new(|| vec![OpenAiTool::LocalShell {}]);
+    })
+}
 
 /// Returns JSON values that are compatible with Function Calling in the
 /// Responses API:
 /// https://platform.openai.com/docs/guides/function-calling?api-mode=responses
 pub(crate) fn create_tools_json_for_responses_api(
     prompt: &Prompt,
-    model: &str,
+    model_family: &ModelFamily,
     include_plan_tool: bool,
 ) -> crate::error::Result<Vec<serde_json::Value>> {
     // Assemble tool list: built-in tools + any extra tools from the prompt.
-    let default_tools = if model.starts_with("codex") {
-        &DEFAULT_CODEX_MODEL_TOOLS
-    } else {
-        &DEFAULT_TOOLS
-    };
-    let mut tools_json = Vec::with_capacity(default_tools.len() + prompt.extra_tools.len());
-    for t in default_tools.iter() {
-        tools_json.push(serde_json::to_value(t)?);
+    let mut openai_tools = vec![create_shell_tool()];
+    if model_family.uses_local_shell_tool {
+        openai_tools.push(OpenAiTool::LocalShell {});
+    }
+
+    let mut tools_json = Vec::with_capacity(openai_tools.len() + prompt.extra_tools.len() + 1);
+    for tool in openai_tools.iter() {
+        tools_json.push(serde_json::to_value(tool)?);
     }
     tools_json.extend(
         prompt
@@ -107,13 +103,13 @@ pub(crate) fn create_tools_json_for_responses_api(
 /// https://platform.openai.com/docs/guides/function-calling?api-mode=chat
 pub(crate) fn create_tools_json_for_chat_completions_api(
     prompt: &Prompt,
-    model: &str,
+    model_family: &ModelFamily,
     include_plan_tool: bool,
 ) -> crate::error::Result<Vec<serde_json::Value>> {
     // We start with the JSON for the Responses API and than rewrite it to match
     // the chat completions tool call format.
     let responses_api_tools_json =
-        create_tools_json_for_responses_api(prompt, model, include_plan_tool)?;
+        create_tools_json_for_responses_api(prompt, model_family, include_plan_tool)?;
     let tools_json = responses_api_tools_json
         .into_iter()
         .filter_map(|mut tool| {