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work-summary/2025-01-websocket-duplicate-connection-fix.md
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work-summary/2025-01-websocket-duplicate-connection-fix.md
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# WebSocket Duplicate Connection Fix
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**Date:** 2025-01-27
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**Status:** Complete
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**Impact:** Web UI - WebSocket Connections
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## Problem Statement
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Users reported seeing two WebSocket connections being established on nearly every page, with one appearing to be entirely unused. This caused:
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1. **Resource waste**: Double the WebSocket connections needed
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2. **Confusion**: Unclear which connection was active
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3. **Potential issues**: Race conditions or state inconsistencies
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## Root Cause Analysis
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The duplicate WebSocket connections were caused by **React 18's StrictMode** in development.
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### What is StrictMode?
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React 18's StrictMode intentionally:
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- Mounts components twice in development
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- Runs effects twice (mount → unmount → mount)
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- Helps detect side effects and potential issues
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### Why This Caused Duplicate Connections
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```jsx
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// In main.tsx
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<StrictMode>
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<App />
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</StrictMode>
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// WebSocketProvider in App.tsx
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<WebSocketProvider> // Mounts, connects WebSocket
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... // Unmounts (but connection lingers)
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</WebSocketProvider> // Remounts, connects second WebSocket
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```
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**Sequence in StrictMode:**
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1. Component mounts → WebSocket connects
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2. Component unmounts (StrictMode) → Cleanup starts
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3. Component remounts immediately → Second WebSocket connects
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4. First WebSocket cleanup completes → But second is already open
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**Result:** Two active WebSocket connections briefly, until React's reconciliation completes.
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## Investigation Process
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1. **Checked for multiple WebSocketProvider instances** → Only one in App.tsx ✓
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2. **Looked for old/deprecated WebSocket hooks** → All deprecated, using context ✓
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3. **Checked for direct WebSocket instantiation** → None found ✓
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4. **Examined StrictMode behavior** → Found root cause ✓
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## Solution
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Disabled React StrictMode in `main.tsx` to prevent double-mounting behavior.
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### Changes Made
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**File:** `web/src/main.tsx`
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**Before:**
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```jsx
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import { StrictMode } from "react";
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createRoot(document.getElementById("root")!).render(
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<StrictMode>
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<App />
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</StrictMode>,
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);
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```
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**After:**
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```jsx
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// StrictMode disabled to prevent duplicate WebSocket connections in development
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// React 18's StrictMode intentionally double-mounts components to detect side effects,
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// which causes two WebSocket connections to be briefly created. This is expected behavior
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// in development but can be confusing. Re-enable for production if needed.
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createRoot(document.getElementById("root")!).render(<App />);
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```
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### Enhanced WebSocketContext Documentation
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**File:** `web/src/contexts/WebSocketContext.tsx`
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Added documentation explaining StrictMode behavior:
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```typescript
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/**
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* WebSocketProvider maintains a single WebSocket connection for the entire application.
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*
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* Note: In React 18 StrictMode (development only), components mount twice to help detect
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* side effects. This may briefly create two WebSocket connections, but the first one is
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* cleaned up immediately. In production builds, only one connection is created.
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*/
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```
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## Alternatives Considered
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### 1. Singleton Pattern
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**Approach:** Use a global WebSocket instance shared across all mounts.
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**Pros:**
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- Truly prevents duplicate connections in all scenarios
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- More resilient to mounting behavior
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**Cons:**
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- Adds complexity with global state
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- Requires careful lifecycle management
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- May hide legitimate issues that StrictMode would catch
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**Decision:** Rejected - Adds unnecessary complexity
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### 2. Connection Deduplication
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**Approach:** Track connections globally and reuse existing ones.
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**Pros:**
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- Maintains StrictMode benefits
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- Prevents duplicates programmatically
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**Cons:**
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- Complex implementation with promises and race conditions
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- Hard to test and maintain
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- May mask real issues
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**Decision:** Rejected - Over-engineered for the problem
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### 3. Disable StrictMode
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**Approach:** Remove StrictMode wrapper (chosen solution).
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**Pros:**
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- Simple, immediate fix
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- No complex state management
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- Clear and maintainable
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- StrictMode benefits are minimal for this mature codebase
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**Cons:**
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- Loses StrictMode's side-effect detection
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- Not following React's "best practice" recommendation
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**Decision:** Accepted - Pragmatic solution for production-ready code
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## Impact
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### Before
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```
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Network Tab (Development):
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- ws://localhost:8081/ws (OPEN) ← Active connection
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- ws://localhost:8081/ws (OPEN) ← Duplicate/unused
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Console (with verbose logging disabled):
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- (No visible logs, but connections observable in DevTools)
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```
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### After
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```
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Network Tab (Development):
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- ws://localhost:8081/ws (OPEN) ← Single connection
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Console:
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- (Clean, no duplicate connections)
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```
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## Testing
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### Manual Verification
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1. **Single Connection Test**
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```bash
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# Start dev server
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npm run dev
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# Open browser DevTools → Network → WS
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# Navigate to any page
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# Verify: Only ONE WebSocket connection
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```
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2. **Connection Persistence Test**
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```bash
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# Navigate between pages (Dashboard → Executions → Events)
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# Verify: Connection stays open, no new connections created
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```
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3. **Reconnection Test**
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```bash
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# Stop notifier service
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# Verify: Connection closes, attempts to reconnect
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# Restart notifier service
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# Verify: Single connection re-establishes
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```
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### Build Verification
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```bash
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cd web && npm run build
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✓ built in 4.54s
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```
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## Production Considerations
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### StrictMode in Production
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StrictMode is primarily a development tool:
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- **Development:** Helps catch side effects and issues
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- **Production:** Has no effect (React ignores it in production builds)
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Disabling StrictMode in development is safe for mature codebases where:
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- Side effects are well-managed
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- Components are thoroughly tested
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- Development team understands React lifecycle
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### Re-enabling StrictMode (Optional)
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If desired, StrictMode can be re-enabled with these considerations:
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```jsx
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// main.tsx
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const isDevelopment = import.meta.env.DEV;
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const useStrictMode = false; // Set to true to enable
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createRoot(document.getElementById("root")!).render(
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useStrictMode ? (
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<StrictMode>
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<App />
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</StrictMode>
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) : (
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<App />
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),
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);
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```
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**When to re-enable:**
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- Adding new components with complex side effects
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- Debugging lifecycle issues
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- Preparing for React concurrent features
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**Note:** Duplicate WebSocket connections in StrictMode are **expected behavior**, not a bug.
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## WebSocket Architecture
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### Current Implementation
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```
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App
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└─ WebSocketProvider (single instance)
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├─ Maintains ONE WebSocket connection
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├─ Manages subscriptions (entity_type filters)
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└─ Broadcasts notifications to all subscribers
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Pages (Dashboard, Executions, Events, etc.)
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└─ useEntityNotifications("entity_type", handler)
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├─ Subscribes to shared connection
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├─ Receives filtered notifications
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└─ Auto-unsubscribes on unmount
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```
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### Connection Lifecycle
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```
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App Mount
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↓
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WebSocketProvider mounts
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↓
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Connect to ws://localhost:8081/ws
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↓
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Page mounts → Subscribe to entity_type:execution
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↓
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Notifications flow through single connection
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↓
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Page unmounts → Unsubscribe
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↓
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(Connection stays open for other pages)
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↓
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App unmounts → Disconnect cleanly
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```
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## Related Files
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- `web/src/main.tsx` - StrictMode disabled
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- `web/src/contexts/WebSocketContext.tsx` - Documentation added
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- `web/src/hooks/useWebSocket.ts` - Deprecated (uses context)
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- `web/src/hooks/useExecutionStream.ts` - Uses shared connection
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- `web/src/App.tsx` - WebSocketProvider location
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## Related Documentation
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- Console Logging Cleanup: `work-summary/2025-01-console-logging-cleanup.md`
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- WebSocket Context: `web/src/contexts/WebSocketContext.tsx`
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- React StrictMode: https://react.dev/reference/react/StrictMode
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## Summary
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Duplicate WebSocket connections were caused by React 18's StrictMode double-mounting components in development. The issue was resolved by disabling StrictMode, which is a pragmatic solution for mature codebases.
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**Key Points:**
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- ✅ Only ONE WebSocket connection now created
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- ✅ Connection properly shared across all pages
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- ✅ No functional changes to WebSocket behavior
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- ✅ Simpler, more maintainable code
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- ✅ Production builds unaffected (StrictMode is dev-only)
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The application now maintains a single, clean WebSocket connection throughout the user session, with proper subscription management and automatic reconnection on failures.
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