assistant2: Restore tool uses when loading saved threads (#25942)

This PR makes it so tool uses are restored when loading saved threads in
Assistant 2.

Release Notes:

- N/A

crates/assistant2/src/thread_store.rs

@@ -14,7 +14,7 @@ use gpui::{
 };
 use heed::types::{SerdeBincode, SerdeJson};
 use heed::Database;
-use language_model::Role;
+use language_model::{LanguageModelToolUseId, Role};
 use project::Project;
 use serde::{Deserialize, Serialize};
 use util::ResultExt as _;
@@ -113,6 +113,24 @@ impl ThreadStore {
                         id: message.id,
                         role: message.role,
                         text: message.text.clone(),
+                        tool_uses: thread
+                            .tool_uses_for_message(message.id)
+                            .into_iter()
+                            .map(|tool_use| SavedToolUse {
+                                id: tool_use.id,
+                                name: tool_use.name,
+                                input: tool_use.input,
+                            })
+                            .collect(),
+                        tool_results: thread
+                            .tool_results_for_message(message.id)
+                            .into_iter()
+                            .map(|tool_result| SavedToolResult {
+                                tool_use_id: tool_result.tool_use_id.clone(),
+                                is_error: tool_result.is_error,
+                                content: tool_result.content.clone(),
+                            })
+                            .collect(),
                     })
                     .collect(),
             };
@@ -239,11 +257,29 @@ pub struct SavedThread {
     pub messages: Vec<SavedMessage>,
 }
 
-#[derive(Serialize, Deserialize)]
+#[derive(Debug, Serialize, Deserialize)]
 pub struct SavedMessage {
     pub id: MessageId,
     pub role: Role,
     pub text: String,
+    #[serde(default)]
+    pub tool_uses: Vec<SavedToolUse>,
+    #[serde(default)]
+    pub tool_results: Vec<SavedToolResult>,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct SavedToolUse {
+    pub id: LanguageModelToolUseId,
+    pub name: SharedString,
+    pub input: serde_json::Value,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct SavedToolResult {
+    pub tool_use_id: LanguageModelToolUseId,
+    pub is_error: bool,
+    pub content: Arc<str>,
 }
 
 struct GlobalThreadsDatabase(