Support changing reasoning effort (#2435)

https://github.com/user-attachments/assets/50198ee8-5915-47a3-bb71-69af65add1ef

Building up on #2431 #2428

codex-rs/common/src/lib.rs

@@ -29,3 +29,5 @@ mod config_summary;
 pub use config_summary::create_config_summary_entries;
 // Shared fuzzy matcher (used by TUI selection popups and other UI filtering)
 pub mod fuzzy_match;
+// Shared model presets used by TUI and MCP server
+pub mod model_presets;

codex-rs/common/src/model_presets.rs

@@ -0,0 +1,54 @@
+use codex_core::protocol_config_types::ReasoningEffort;
+
+/// A simple preset pairing a model slug with a reasoning effort.
+#[derive(Debug, Clone, Copy)]
+pub struct ModelPreset {
+    /// Stable identifier for the preset.
+    pub id: &'static str,
+    /// Display label shown in UIs.
+    pub label: &'static str,
+    /// Short human description shown next to the label in UIs.
+    pub description: &'static str,
+    /// Model slug (e.g., "gpt-5").
+    pub model: &'static str,
+    /// Reasoning effort to apply for this preset.
+    pub effort: ReasoningEffort,
+}
+
+/// Built-in list of model presets that pair a model with a reasoning effort.
+///
+/// Keep this UI-agnostic so it can be reused by both TUI and MCP server.
+pub fn builtin_model_presets() -> &'static [ModelPreset] {
+    // Order reflects effort from minimal to high.
+    const PRESETS: &[ModelPreset] = &[
+        ModelPreset {
+            id: "gpt-5-minimal",
+            label: "gpt-5 minimal",
+            description: "— Fastest responses with very limited reasoning; ideal for coding, instructions, or lightweight tasks.",
+            model: "gpt-5",
+            effort: ReasoningEffort::Minimal,
+        },
+        ModelPreset {
+            id: "gpt-5-low",
+            label: "gpt-5 low",
+            description: "— Balances speed with some reasoning; useful for straightforward queries and short explanations.",
+            model: "gpt-5",
+            effort: ReasoningEffort::Low,
+        },
+        ModelPreset {
+            id: "gpt-5-medium",
+            label: "gpt-5 medium",
+            description: "— Default setting; provides a solid balance of reasoning depth and latency for general-purpose tasks.",
+            model: "gpt-5",
+            effort: ReasoningEffort::Medium,
+        },
+        ModelPreset {
+            id: "gpt-5-high",
+            label: "gpt-5 high",
+            description: "— Maximizes reasoning depth for complex or ambiguous problems.",
+            model: "gpt-5",
+            effort: ReasoningEffort::High,
+        },
+    ];
+    PRESETS
+}