Implement Action Dialect function for interactive walkthrough buttons

- Add Action function for creating interactive buttons in walkthroughs
- Simple pass-through function with description, button text, and optional tell_agent
- Register Action function in DialectInterpreter for both normal and test modes
- Add comprehensive test with expect-test validation
- Enables interactive elements in walkthroughs

Example usage:
{"action": {"description": "Generate code", "button": "Generate", "tell_agent": "Create auth system"}}

Author: nikomatsakis

server/src/ide.rs

@@ -372,3 +372,45 @@ fn process_file(
     }
     Vec::new()
 }
+
+/// Create an interactive action button for walkthroughs.
+///
+/// Examples:
+/// - `{"action": {"description": "Click to run tests", "button": "Run Tests"}}`
+/// - `{"action": {"description": "Generate boilerplate", "button": "Generate", "tell_agent": "Generate user authentication boilerplate"}}`
+#[derive(Deserialize)]
+pub struct Action {
+    /// Description shown to user
+    pub description: String,
+    
+    /// Button text
+    pub button: String,
+    
+    /// Optional text to send to agent when clicked
+    pub tell_agent: Option<String>,
+}
+
+#[derive(Serialize)]
+pub struct ResolvedAction {
+    pub description: String,
+    pub button: String,
+    pub tell_agent: Option<String>,
+}
+
+impl<U: IpcClient> DialectFunction<U> for Action {
+    type Output = ResolvedAction;
+
+    const DEFAULT_FIELD_NAME: Option<&'static str> = None;
+
+    async fn execute(
+        self,
+        _interpreter: &mut DialectInterpreter<U>,
+    ) -> anyhow::Result<Self::Output> {
+        // Action is already resolved, just pass through
+        Ok(ResolvedAction {
+            description: self.description,
+            button: self.button,
+            tell_agent: self.tell_agent,
+        })
+    }
+}

server/src/ide/test.rs

@@ -729,3 +729,39 @@ async fn test_comment_function_with_symbol_def() {
     "#]]
     .assert_debug_eq(&result);
 }
+
+#[tokio::test]
+async fn test_action_function() {
+    use expect_test::expect;
+    
+    let mock_client = MockIpcClient::new();
+    let mut interpreter = DialectInterpreter::new(mock_client);
+    interpreter.add_function::<FindDefinitions>();
+    interpreter.add_function::<FindReferences>();
+    interpreter.add_function::<crate::ide::Search>();
+    interpreter.add_function::<crate::ide::GitDiff>();
+    interpreter.add_function::<crate::ide::Comment>();
+    interpreter.add_function::<crate::ide::Action>();
+    
+    // Test action with tell_agent
+    let program = serde_json::json!({
+        "action": {
+            "description": "Generate authentication boilerplate code",
+            "button": "Generate Auth",
+            "tell_agent": "Create a complete authentication system with login, logout, and middleware"
+        }
+    });
+    
+    let result = interpreter.evaluate(program).await;
+    
+    expect![[r#"
+        Ok(
+            Object {
+                "button": String("Generate Auth"),
+                "description": String("Generate authentication boilerplate code"),
+                "tell_agent": String("Create a complete authentication system with login, logout, and middleware"),
+            },
+        )
+    "#]]
+    .assert_debug_eq(&result);
+}

server/src/server.rs

@@ -74,6 +74,7 @@ impl DialecticServer {
         interpreter.add_function::<crate::ide::Search>();
         interpreter.add_function::<crate::ide::GitDiff>();
         interpreter.add_function::<crate::ide::Comment>();
+        interpreter.add_function::<crate::ide::Action>();
 
         Ok(Self {
             ipc: ipc.clone(),
@@ -178,6 +179,7 @@ impl DialecticServer {
         interpreter.add_function::<crate::ide::Search>();
         interpreter.add_function::<crate::ide::GitDiff>();
         interpreter.add_function::<crate::ide::Comment>();
+        interpreter.add_function::<crate::ide::Action>();
 
         Self {
             ipc,