Refactor mountNode to build fiber tree alongside host instances

src/host/config.ts

@@ -1,6 +1,7 @@
 import type { UNode, UElement, URoot, ComponentFn, UComponent } from "../core/schema.js";
 import { isURoot, isUPrimitive } from "../core/schema.js";
 import { Context } from "../core/context.js";
+import type { Fiber } from "./fiber.js";
 
 export interface HostConfig<TTag extends string, Instance, RootCtx> {
   name: string;
@@ -34,6 +35,7 @@ export interface Root<TTag extends string, Instance, RootCtx> {
   ctx: RootCtx;
   container: unknown;
   context: Context;
+  rootFiber: Fiber<Instance> | null;
   render(node: UNode): void;
   unmount(): void;
 }
@@ -47,46 +49,70 @@ export function createRoot<TTag extends string, Instance, RootCtx>(
   const ctx = host.createRootContext(container, options, context);
   const rootContext = context ?? new Context();
 
-  function mountNode(node: UNode, parentInst?: Instance): Instance | undefined {
+  function mountNode(node: UNode, parentFiber: Fiber<Instance> | null): Fiber<Instance> | undefined {
     if (node == null || node === false) return undefined;
 
     if (isUPrimitive(node)) {
       const text = node === null ? "" : String(node);
+      const parentInst = parentFiber?.instance;
       const t = host.createTextInstance(text, ctx, parentInst);
       if (parentInst) host.appendChild(parentInst, t, ctx);
       host.emit?.("instance.create", `text_${Date.now()}`, { kind: "text", value: text });
-      return t;
+      const fiber: Fiber<Instance> = {
+        instance: t,
+        tag: "#text",
+        props: { text },
+        key: undefined,
+        children: [],
+        parent: parentFiber,
+        effect: null,
+        signalDisposers: [],
+        prevProps: null,
+      };
+      if (parentFiber) parentFiber.children.push(fiber);
+      return fiber;
     }
 
     if (isURoot(node)) {
       for (const child of node.children) {
-        mountNode(child, parentInst);
+        mountNode(child, parentFiber);
       }
-      return parentInst;
+      return parentFiber ?? undefined;
     }
 
-    // node must be a UElement here
     const el = node as UElement;
 
-    // Function component — type is a function (runtime-only, before resolution)
     if (typeof el.type === "function") {
       const component = el.type as ComponentFn;
       const out = component({ ...el.props, children: el.children });
       host.emit?.("component.invoke", `comp_${Date.now()}`, { type: (component as unknown as UComponent).displayName ?? "anonymous" });
-      return mountNode(out, parentInst);
+      return mountNode(out, parentFiber);
     }
 
-    // Intrinsic element
     const tag = el.type as TTag;
+    const parentInst = parentFiber?.instance;
     const inst = host.createInstance(tag, el.props as Record<string, unknown>, ctx, parentInst);
     host.emit?.("instance.create", `${tag}_${Date.now()}`, { kind: "element", tag, props: el.props });
 
+    const fiber: Fiber<Instance> = {
+      instance: inst,
+      tag,
+      props: el.props as Record<string, unknown>,
+      key: el.key,
+      children: [],
+      parent: parentFiber,
+      effect: null,
+      signalDisposers: [],
+      prevProps: null,
+    };
+
     for (const child of el.children) {
-      mountNode(child, inst);
+      mountNode(child, fiber);
     }
 
     if (parentInst) host.appendChild(parentInst, inst, ctx);
-    return inst;
+    if (parentFiber) parentFiber.children.push(fiber);
+    return fiber;
   }
 
   return {
@@ -94,11 +120,24 @@ export function createRoot<TTag extends string, Instance, RootCtx>(
     ctx,
     container,
     context: rootContext,
+    rootFiber: null,
     render(node: UNode) {
+      const root: Fiber<Instance> = {
+        instance: undefined as unknown as Instance,
+        tag: "#root",
+        props: {},
+        key: undefined,
+        children: [],
+        parent: null,
+        effect: null,
+        signalDisposers: [],
+        prevProps: null,
+      };
       const payloadChildren = isURoot(node) ? (node as URoot).children : [node];
       for (const child of payloadChildren) {
-        mountNode(child, undefined);
+        mountNode(child, root);
       }
+      this.rootFiber = root;
       host.finalizeRoot?.(ctx);
       host.emit?.("root.render", `root_${Date.now()}`, { childCount: payloadChildren.length });
     },