feat: make it possible to toggle mouse mode in the Rust TUI (#971)

I did a bit of research to understand why I could not use my mouse to
drag to select text to copy to the clipboard in iTerm.

Apparently https://github.com/openai/codex/pull/641 to enable mousewheel
scrolling broke this functionality. It seems that, unless we put in a
bit of effort, we can have drag-to-select or scrolling, but not both.
Though if you know the trick to hold down `Option` will dragging with
the mouse in iTerm, you can probably get by with this. (I did not know
about this option prior to researching this issue.)

Nevertheless, users may still prefer to disable mouse capture
altogether, so this PR introduces:

* the ability to set `tui.disable_mouse_capture = true` in `config.toml`
to disable mouse capture
* a new command, `/toggle-mouse-mode` to toggle mouse capture

codex-rs/core/src/config.rs

@@ -88,6 +88,9 @@ pub struct Config {
     /// Optional URI-based file opener. If set, citations to files in the model
     /// output will be hyperlinked using the specified URI scheme.
     pub file_opener: UriBasedFileOpener,
+
+    /// Collection of settings that are specific to the TUI.
+    pub tui: Tui,
 }
 
 /// Settings that govern if and what will be written to `~/.codex/history.jsonl`.
@@ -111,6 +114,23 @@ pub enum HistoryPersistence {
     None,
 }
 
+/// Collection of settings that are specific to the TUI.
+#[derive(Deserialize, Debug, Clone, PartialEq, Default)]
+pub struct Tui {
+    /// By default, mouse capture is enabled in the TUI so that it is possible
+    /// to scroll the conversation history with a mouse. This comes at the cost
+    /// of not being able to use the mouse to select text in the TUI.
+    /// (Most terminals support a modifier key to allow this. For example,
+    /// text selection works in iTerm if you hold down the `Option` key while
+    /// clicking and dragging.)
+    ///
+    /// Setting this option to `true` disables mouse capture, so scrolling with
+    /// the mouse is not possible, though the keyboard shortcuts e.g. `b` and
+    /// `space` still work. This allows the user to select text in the TUI
+    /// using the mouse without needing to hold down a modifier key.
+    pub disable_mouse_capture: bool,
+}
+
 #[derive(Deserialize, Debug, Copy, Clone, PartialEq)]
 pub enum UriBasedFileOpener {
     #[serde(rename = "vscode")]
@@ -197,6 +217,9 @@ pub struct ConfigToml {
     /// Optional URI-based file opener. If set, citations to files in the model
     /// output will be hyperlinked using the specified URI scheme.
     pub file_opener: Option<UriBasedFileOpener>,
+
+    /// Collection of settings that are specific to the TUI.
+    pub tui: Option<Tui>,
 }
 
 impl ConfigToml {
@@ -391,6 +414,7 @@ impl Config {
             codex_home,
             history,
             file_opener: cfg.file_opener.unwrap_or(UriBasedFileOpener::VsCode),
+            tui: cfg.tui.unwrap_or_default(),
         };
         Ok(config)
     }
@@ -727,6 +751,7 @@ disable_response_storage = true
                 codex_home: fixture.codex_home(),
                 history: History::default(),
                 file_opener: UriBasedFileOpener::VsCode,
+                tui: Tui::default(),
             },
             o3_profile_config
         );
@@ -763,6 +788,7 @@ disable_response_storage = true
             codex_home: fixture.codex_home(),
             history: History::default(),
             file_opener: UriBasedFileOpener::VsCode,
+            tui: Tui::default(),
         };
 
         assert_eq!(expected_gpt3_profile_config, gpt3_profile_config);
@@ -814,6 +840,7 @@ disable_response_storage = true
             codex_home: fixture.codex_home(),
             history: History::default(),
             file_opener: UriBasedFileOpener::VsCode,
+            tui: Tui::default(),
         };
 
         assert_eq!(expected_zdr_profile_config, zdr_profile_config);