feat: component event callbacks + function prop forwarding

- ComponentUse wraps Assign/MethodCall/Block props as arrow functions
- Component prop wrapper preserves function props (typeof check)
- Event handler fallthrough calls function-type identifiers
- New: examples/callback-demo.ds with Button onClick callbacks
- All existing examples build successfully

compiler/ds-codegen/src/js_emitter.rs

@@ -467,12 +467,12 @@ impl JsEmitter {
         self.emit_line(&format!("function DS_{}(props, __children) {{", comp.name));
         self.indent += 1;
         // Destructure props into local signal-compatible variables
-        // Props may be raw values or signals — wrap in a signal-like accessor
+        // Props may be raw values, signals, or callback functions
         for p in &comp.props {
-            // Create a signal-like wrapper: if prop is already a signal, use it; otherwise wrap
+            // Create a signal-like wrapper: if prop is a function, keep as-is; if already a signal, use it; otherwise wrap
             self.emit_line(&format!(
-                "const {} = (props.{} !== undefined && props.{} !== null) ? (typeof props.{} === 'object' && 'value' in props.{} ? props.{} : {{ get value() {{ return props.{}; }} }}) : {{ get value() {{ return \"\"; }} }};",
-                p.name, p.name, p.name, p.name, p.name, p.name, p.name
+                "const {} = (typeof props.{} === 'function') ? props.{} : (props.{} !== undefined && props.{} !== null) ? (typeof props.{} === 'object' && 'value' in props.{} ? props.{} : {{ get value() {{ return props.{}; }} }}) : {{ get value() {{ return \"\"; }} }};",
+                p.name, p.name, p.name, p.name, p.name, p.name, p.name, p.name, p.name
             ));
         }
         let root_id = self.emit_view_expr(&comp.body, graph);
@@ -901,7 +901,18 @@ impl JsEmitter {
             Expr::ComponentUse { name, props, children } => {
                 let node_var = self.next_node_id();
                 let props_js: Vec<String> = props.iter()
-                    .map(|(k, v)| format!("{}: {}", k, self.emit_expr(v)))
+                    .map(|(k, v)| {
+                        // Detect callback props (assignments, method calls, blocks)
+                        let is_callback = matches!(v,
+                            Expr::Assign(_, _, _) | Expr::MethodCall(_, _, _) | Expr::Block(_)
+                        );
+                        if is_callback {
+                            let handler_js = self.emit_event_handler_expr(v);
+                            format!("{}: () => {{ {}; DS.flush() }}", k, handler_js)
+                        } else {
+                            format!("{}: {}", k, self.emit_expr(v))
+                        }
+                    })
                     .collect();
                 if children.is_empty() {
                     self.emit_line(&format!("const {} = DS_{}({{ {} }});", node_var, name, props_js.join(", ")));
@@ -1344,7 +1355,14 @@ impl JsEmitter {
                 let stmts: Vec<String> = exprs.iter().map(|e| self.emit_event_handler_expr(e)).collect();
                 stmts.join("; ")
             }
-            _ => self.emit_expr(expr),
+            _ => {
+                // For plain identifiers that might be callback props, call them
+                if let Expr::Ident(name) = expr {
+                    format!("if (typeof {} === 'function') {}()", name, name)
+                } else {
+                    self.emit_expr(expr)
+                }
+            }
         }
     }
 

examples/callback-demo.ds

@@ -0,0 +1,23 @@
+-- DreamStack Callback Demo
+-- Tests component event callbacks
+
+import { Card } from "../registry/components/card"
+import { Button } from "../registry/components/button"
+
+let count = 0
+let message = "Click a button"
+
+view main = column [
+  text "🔗 Component Callbacks" { variant: "title" }
+  text "Components can trigger parent actions" { variant: "subtitle" }
+
+  Card { title: "Using Button Component", subtitle: "callback props" } [
+    text "Count: {count}" { variant: "title" }
+    text message { variant: "subtitle" }
+    row [
+      Button { label: "+1", onClick: count += 1, variant: "primary" }
+      Button { label: "-1", onClick: count -= 1, variant: "secondary" }
+      Button { label: "Reset", onClick: count = 0, variant: "ghost" }
+    ]
+  ]
+]