Allow displaying diffs in the ui. (#8)

Reviewed-on: #8
Co-authored-by: Drew Galbraith <drew@tiramisu.one>
Co-committed-by: Drew Galbraith <drew@tiramisu.one>

src/tui/mod.rs

@@ -12,6 +12,7 @@
 mod events;
 mod input;
 mod render;
+pub(crate) mod tool_display;
 
 use std::io::{self, Stdout};
 use std::time::Duration;
@@ -54,10 +55,27 @@ pub enum Mode {
     Command,
 }
 
+/// A single message in the TUI's display list.
+///
+/// Unlike `ConversationMessage` (which models the API wire format), this struct
+/// represents a rendered row in the conversation pane. Tool invocations get their
+/// own `DisplayMessage` with a `tool_use_id` so that in-place replacement works:
+/// the approval message becomes the executing message, then the result message.
+#[derive(Debug, Clone)]
+pub struct DisplayMessage {
+    /// Who authored this message (tool messages use `Assistant`).
+    pub role: Role,
+    /// Pre-formatted content for rendering.
+    pub content: String,
+    /// When set, this message can be replaced in-place by a later event carrying
+    /// the same tool-use ID (e.g. executing -> result).
+    pub tool_use_id: Option<String>,
+}
+
 /// The UI-layer view of a conversation: rendered messages and the current input buffer.
 pub struct AppState {
-    /// All conversation turns rendered as (role, content) pairs.
-    pub messages: Vec<(Role, String)>,
+    /// All conversation turns rendered as display messages.
+    pub messages: Vec<DisplayMessage>,
     /// The current contents of the input box.
     pub input: String,
     /// Vertical scroll offset for the output pane (lines from top).