Add MCP introspection support for Electron frontend with Copilot agent integration (#916)

.github/copilot-instructions.md

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+# GitHub Copilot Agent Instructions for MQTT Explorer
+
+## Project Setup
+
+### Building and Running
+
+```bash
+# Install dependencies
+yarn install
+
+# Build the project
+yarn build
+
+# Start the application
+yarn start
+
+# Start in development mode
+yarn dev
+```
+
+### Running with MCP Introspection (for testing)
+
+```bash
+# Build first
+yarn build
+
+# Start with MCP introspection enabled
+electron . --enable-mcp-introspection
+
+# Or with custom port
+electron . --enable-mcp-introspection --remote-debugging-port=9223
+```
+
+## Writing Tests
+
+### Requirements for All Tests
+
+1. **Tests MUST be deterministic** - They should produce the same results every time they run
+2. **Tests MUST be independent** - Each test should be able to run in isolation without depending on other tests
+3. **Include screenshots** - Visual verification is required for UI changes
+4. **Handle asynchronous operations properly** - This is an MQTT message queue tool
+
+### Handling MQTT Asynchronous Operations
+
+MQTT is inherently asynchronous. When writing tests:
+
+- **Wait for message propagation**: Use proper wait strategies (e.g., `await page.waitForSelector()`, `await sleep()`)
+- **Don't assume immediate updates**: Messages take time to send, receive, and update the UI
+- **Use event-based waiting**: Wait for specific UI elements or state changes rather than fixed timeouts when possible
+- **Account for network latency**: MQTT broker communication involves network round trips
+
+### Example Test Pattern
+
+```typescript
+// 1. Perform action (e.g., publish message)
+await publishMessage(topic, payload)
+
+// 2. Wait for UI to update (not just arbitrary sleep)
+await page.waitForSelector(`text="${expectedValue}"`, { timeout: 5000 })
+
+// 3. Verify state
+const value = await page.textContent('.message-value')
+expect(value).toBe(expectedValue)
+
+// 4. Take screenshot for verification
+await page.screenshot({ path: 'test-result.png' })
+```
+
+### Running Tests
+
+```bash
+# Run all tests
+yarn test
+
+# Run specific test suites
+yarn test:app
+yarn test:backend
+yarn test:mcp
+
+# Run linters
+yarn lint
+yarn lint:fix
+```
+
+## MCP Introspection Testing
+
+The project supports MCP (Model Context Protocol) for automated testing with Playwright:
+
+- Use `yarn test:mcp` to run automated UI tests
+- Tests launch the app with remote debugging enabled on port 9222
+- Connect to `http://localhost:9222` via Chrome DevTools Protocol
+
+## Project Structure
+
+- `app/` - Frontend React application
+- `backend/` - Backend models, tests, and connection management
+- `src/` - Electron main process and bindings
+- `src/spec/` - Test specifications including MCP introspection tests
+
+## Important Notes
+
+- Always run `yarn build` before starting the application
+- The app uses Electron (see `package.json` for version)
+- MQTT communication is handled via [mqttjs](https://github.com/mqttjs/MQTT.js)
+- All code changes should pass linting (`yarn lint`)