diff --git a/renderers/web_core/CHANGELOG.md b/renderers/web_core/CHANGELOG.md
index 4f7f5b27f..3bdaa6c7f 100644
--- a/renderers/web_core/CHANGELOG.md
+++ b/renderers/web_core/CHANGELOG.md
@@ -1,3 +1,9 @@
+## 0.8.5
+
+- Add `V8ErrorConstructor` interface to be able to access V8-only 
+  `captureStackTrace` method in errors.
+- Removes dependency from `v0_8` to `v0_9` by duplicating the `errors.ts` file.
+
 ## 0.8.4
 
 - Tweak v0.8 Schema for Button and TextField to better match the spec.
@@ -5,9 +11,3 @@
 ## 0.8.3
 
 - The `MarkdownRenderer` type is now async and returns a `Promise<string>`.
-
-## 0.8.2
-
-## 0.8.1
-
-## 0.8.0
diff --git a/renderers/web_core/package.json b/renderers/web_core/package.json
index 7cfb57aa4..9ad46f001 100644
--- a/renderers/web_core/package.json
+++ b/renderers/web_core/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@a2ui/web_core",
-  "version": "0.8.4",
+  "version": "0.8.5",
   "description": "A2UI Core Library",
   "main": "./dist/src/v0_8/index.js",
   "types": "./dist/src/v0_8/index.d.ts",
@@ -77,7 +77,7 @@
       "clean": "if-file-deleted"
     },
     "test": {
-      "command": "node --test \"dist/**/*.test.js\"",
+      "command": "node --test dist",
       "dependencies": [
         "build"
       ]
diff --git a/renderers/web_core/src/v0_8/data/model-processor.ts b/renderers/web_core/src/v0_8/data/model-processor.ts
index 20bcdcdf1..b5873464d 100644
--- a/renderers/web_core/src/v0_8/data/model-processor.ts
+++ b/renderers/web_core/src/v0_8/data/model-processor.ts
@@ -31,7 +31,7 @@ import {
   MessageProcessor,
 } from "../types/types.js";
 import { A2uiMessageSchema } from "../schema/server-to-client.js";
-import { A2uiStateError, A2uiValidationError } from "../../v0_9/errors.js";
+import { A2uiStateError, A2uiValidationError } from "../errors.js";
 import {
   isComponentArrayReference,
   isObject,
diff --git a/renderers/web_core/src/v0_8/errors.ts b/renderers/web_core/src/v0_8/errors.ts
new file mode 100644
index 000000000..8b0ef2582
--- /dev/null
+++ b/renderers/web_core/src/v0_8/errors.ts
@@ -0,0 +1,86 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * This interface is needed for typescript to allow us to access the V8-only
+ * `captureStackTrace` property in Errors.
+ */
+interface V8ErrorConstructor extends ErrorConstructor {
+  captureStackTrace(targetObject: object, constructorOpt?: Function): void;
+}
+
+/**
+ * Base class for all A2UI specific errors.
+ */
+export class A2uiError extends Error {
+  public readonly code: string;
+
+  constructor(message: string, code: string = "UNKNOWN_ERROR") {
+    super(message);
+    this.name = this.constructor.name;
+    this.code = code;
+
+    // Maintains proper stack trace for where our error was thrown (only available on V8)
+    if ((Error as V8ErrorConstructor).captureStackTrace) {
+      (Error as V8ErrorConstructor).captureStackTrace(this, this.constructor);
+    }
+  }
+}
+
+/**
+ * Thrown when JSON validation fails or schemas are mismatched.
+ */
+export class A2uiValidationError extends A2uiError {
+  constructor(
+    message: string,
+    public readonly details?: any,
+  ) {
+    super(message, "VALIDATION_ERROR");
+  }
+}
+
+/**
+ * Thrown during DataModel mutations (invalid paths, type mismatches).
+ */
+export class A2uiDataError extends A2uiError {
+  constructor(
+    message: string,
+    public readonly path?: string,
+  ) {
+    super(message, "DATA_ERROR");
+  }
+}
+
+/**
+ * Thrown during string interpolation and function evaluation.
+ */
+export class A2uiExpressionError extends A2uiError {
+  constructor(
+    message: string,
+    public readonly expression?: string,
+  ) {
+    super(message, "EXPRESSION_ERROR");
+  }
+}
+
+/**
+ * Thrown for structural issues in the UI tree (missing surfaces, duplicate components).
+ */
+export class A2uiStateError extends A2uiError {
+  constructor(message: string) {
+    super(message, "STATE_ERROR");
+  }
+}
diff --git a/renderers/web_core/src/v0_8/index.ts b/renderers/web_core/src/v0_8/index.ts
index f9a3c22c9..05e8cd1cd 100644
--- a/renderers/web_core/src/v0_8/index.ts
+++ b/renderers/web_core/src/v0_8/index.ts
@@ -21,6 +21,7 @@ export * from "./styles/index.js";
 export * from "./types/colors.js";
 export * from "./types/primitives.js";
 export * from "./types/types.js";
+export * from "./errors.js";
 
 import A2UIClientEventMessage from "./schemas/server_to_client_with_standard_catalog.json" with { type: "json" };
 
diff --git a/renderers/web_core/src/v0_9/errors.ts b/renderers/web_core/src/v0_9/errors.ts
index 1933281bc..8b0ef2582 100644
--- a/renderers/web_core/src/v0_9/errors.ts
+++ b/renderers/web_core/src/v0_9/errors.ts
@@ -14,6 +14,14 @@
  * limitations under the License.
  */
 
+/**
+ * This interface is needed for typescript to allow us to access the V8-only
+ * `captureStackTrace` property in Errors.
+ */
+interface V8ErrorConstructor extends ErrorConstructor {
+  captureStackTrace(targetObject: object, constructorOpt?: Function): void;
+}
+
 /**
  * Base class for all A2UI specific errors.
  */
@@ -26,8 +34,8 @@ export class A2uiError extends Error {
     this.code = code;
 
     // Maintains proper stack trace for where our error was thrown (only available on V8)
-    if (Error.captureStackTrace) {
-      Error.captureStackTrace(this, this.constructor);
+    if ((Error as V8ErrorConstructor).captureStackTrace) {
+      (Error as V8ErrorConstructor).captureStackTrace(this, this.constructor);
     }
   }
 }