feat(config): parse data-shadow attribute on script tag

Adds the boolean field consumed by the upcoming Shadow DOM mount path.
Strict equality with the string "true" — anything else (absent, "false",
"1", "yes", empty) yields false, so accidental opt-in is impossible.

Tests cover the full parseConfig surface (required fields, server-url
derivation, position default) plus the new shadow attribute parsing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/config.ts

@@ -3,6 +3,7 @@ export type WidgetConfig = {
   apiKey: string;
   serverUrl: string;
   position?: 'bottom-right' | 'bottom-left';
+  shadow: boolean;
 };
 
 export function parseConfig(): WidgetConfig | null {
@@ -22,10 +23,11 @@ export function parseConfig(): WidgetConfig | null {
       | 'bottom-right'
       | 'bottom-left'
       | null) ?? 'bottom-right';
+  const shadow = script.getAttribute('data-shadow') === 'true';
 
   if (!botId || !apiKey) return null;
 
-  return { botId, apiKey, serverUrl, position };
+  return { botId, apiKey, serverUrl, position, shadow };
 }
 
 function deriveServerFromSrc(src: string): string {

tests/unit/config.test.ts

@@ -0,0 +1,118 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { parseConfig } from '@/config';
+
+function createScript(
+  attrs: Record<string, string>,
+  src = 'https://cdn.example.com/messenzy-widget.iife.js',
+): HTMLScriptElement {
+  const script = document.createElement('script');
+  script.src = src;
+  for (const [key, value] of Object.entries(attrs)) {
+    script.setAttribute(key, value);
+  }
+  document.head.appendChild(script);
+  return script;
+}
+
+beforeEach(() => {
+  document.head.innerHTML = '';
+  document.body.innerHTML = '';
+});
+
+describe('parseConfig', () => {
+  it('returns null when no script with data-bot-id is present', () => {
+    expect(parseConfig()).toBeNull();
+  });
+
+  it('returns null when data-api-key is missing', () => {
+    createScript({ 'data-bot-id': 'b1' });
+    expect(parseConfig()).toBeNull();
+  });
+
+  it('returns null when data-bot-id is missing', () => {
+    createScript({ 'data-api-key': 'k1' });
+    expect(parseConfig()).toBeNull();
+  });
+
+  it('parses required fields', () => {
+    createScript({ 'data-bot-id': 'b1', 'data-api-key': 'k1' });
+    const config = parseConfig();
+    expect(config).not.toBeNull();
+    expect(config?.botId).toBe('b1');
+    expect(config?.apiKey).toBe('k1');
+  });
+
+  it('derives serverUrl from script src when data-server-url absent', () => {
+    createScript(
+      { 'data-bot-id': 'b1', 'data-api-key': 'k1' },
+      'https://widgets.example.com/path/messenzy.iife.js',
+    );
+    expect(parseConfig()?.serverUrl).toBe('https://widgets.example.com');
+  });
+
+  it('respects explicit data-server-url override', () => {
+    createScript({
+      'data-bot-id': 'b1',
+      'data-api-key': 'k1',
+      'data-server-url': 'https://api.foo.test',
+    });
+    expect(parseConfig()?.serverUrl).toBe('https://api.foo.test');
+  });
+
+  it('defaults position to bottom-right', () => {
+    createScript({ 'data-bot-id': 'b1', 'data-api-key': 'k1' });
+    expect(parseConfig()?.position).toBe('bottom-right');
+  });
+
+  it('parses position bottom-left', () => {
+    createScript({
+      'data-bot-id': 'b1',
+      'data-api-key': 'k1',
+      'data-position': 'bottom-left',
+    });
+    expect(parseConfig()?.position).toBe('bottom-left');
+  });
+
+  describe('shadow attribute (PR B opt-in)', () => {
+    it('shadow=false when data-shadow absent', () => {
+      createScript({ 'data-bot-id': 'b1', 'data-api-key': 'k1' });
+      expect(parseConfig()?.shadow).toBe(false);
+    });
+
+    it('shadow=true when data-shadow="true"', () => {
+      createScript({
+        'data-bot-id': 'b1',
+        'data-api-key': 'k1',
+        'data-shadow': 'true',
+      });
+      expect(parseConfig()?.shadow).toBe(true);
+    });
+
+    it('shadow=false when data-shadow="false"', () => {
+      createScript({
+        'data-bot-id': 'b1',
+        'data-api-key': 'k1',
+        'data-shadow': 'false',
+      });
+      expect(parseConfig()?.shadow).toBe(false);
+    });
+
+    it('shadow=false when data-shadow="" (empty)', () => {
+      createScript({
+        'data-bot-id': 'b1',
+        'data-api-key': 'k1',
+        'data-shadow': '',
+      });
+      expect(parseConfig()?.shadow).toBe(false);
+    });
+
+    it('shadow=false for unrecognized values (e.g. "1", "yes")', () => {
+      createScript({
+        'data-bot-id': 'b1',
+        'data-api-key': 'k1',
+        'data-shadow': '1',
+      });
+      expect(parseConfig()?.shadow).toBe(false);
+    });
+  });
+});