Fix: Resolve Tauri Error 1412 (Chrome_WidgetWin_0) on Windows 11

[pranitaurlam]

Overview

Fixes #1147

This PR resolves the issue where the Tauri frontend exits shortly after startup with Error 1412: Failed to unregister class Chrome_WidgetWin_0 on Windows 11.

Root Cause

Error 1412 (ERROR_CLASS_ALREADY_EXISTS) is a Windows 11 WebView2/Chromium issue that occurs when multiple WebView2 instances attempt to register the same window class name. This causes the window to close prematurely before connecting to backend services.

Changes

1. Added Single-Instance Plugin

• File: frontend/src-tauri/Cargo.toml
• Change: Added tauri-plugin-single-instance = "2.3.1"
• Purpose: Prevents multiple WebView2 instances from running simultaneously

2. Registered Single-Instance Behavior

• File: frontend/src-tauri/src/main.rs
• Change: Configured plugin to focus existing window when second instance is launched
• Purpose: Ensures only one WebView2 instance exists, preventing window class conflicts

3. Enhanced Window Configuration

• File: frontend/src-tauri/tauri.conf.json
• Changes:
  • Added "label": "main" for explicit window identification
  • Added "skipTaskbar": false" for proper Windows 11 taskbar registration
• Purpose: Improves window lifecycle management

Testing

• Tested on Windows 11
• Window stays open and doesn't auto-close
• No Error 1412 in terminal
• Successfully connects to backend services
• Launching second instance focuses first window (no new window created)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have made minimal, necessary changes only
• My changes generate no new warnings
• I have added comments explaining the fix where necessary

Additional Notes

This is a minimal, non-intrusive fix that:

• Doesn't modify existing application logic
• Uses a standard, well-maintained Tauri plugin
• Addresses the root cause rather than suppressing symptoms
• Won't negatively impact macOS/Linux builds

Summary by CodeRabbit

• New Features

  • Added single-instance behavior: launching the app while already running will focus the existing window instead of opening a duplicate.
  • Window metadata updated so the main window is explicitly identified and appears in the taskbar.

• Documentation

  • Updated contributing guide with Jest diagnostic steps to help investigate common test-run warnings.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds single-instance handling to the Tauri desktop app (via tauri-plugin-single-instance), configures the main window label and taskbar visibility, and documents a Jest open-handles diagnostic in CONTRIBUTING.md.

Changes

Cohort / File(s)	Summary
Documentation CONTRIBUTING.md	Added frontend testing note describing the Jest warning "Jest did not exit one second after the test run has completed" and instructing use of npx jest --detectOpenHandles to diagnose/teardown open resources.
Tauri single-instance & window config frontend/src-tauri/Cargo.toml, frontend/src-tauri/src/main.rs, frontend/src-tauri/tauri.conf.json	Added tauri-plugin-single-instance = "2.3.1" and initialized the plugin in main.rs with a callback that focuses the main window when a second instance launches; added label: "main" and skipTaskbar: false to the first window entry in tauri.conf.json.

Sequence Diagram(s)

sequenceDiagram
    participant User as User (second launch)
    participant OS as OS
    participant Plugin as SingleInstancePlugin
    participant App as TauriApp
    participant Window as MainWindow

    User->>OS: launch second instance
    OS->>Plugin: detect existing instance
    Plugin->>App: invoke callback (with args)
    App->>Window: get_webview_window("main")
    App->>Window: set_focus()
    Plugin-->>OS: prevent new instance

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Suggested labels

bug, build

Poem

🐰 I hopped in twice, but found just one home,
A gentle tap brought focus back to the dome,
No twin windows racing across the lawn,
One main hello at the break of dawn,
Nuzzle, focus, and then I’m gone.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Out of Scope Changes check	❓ Inconclusive	The addition of a testing note to CONTRIBUTING.md about Jest warning is tangentially related but not directly required by issue #1147; all other changes are in-scope for fixing the Windows 11 Tauri error.	Clarify whether the CONTRIBUTING.md change is necessary for this PR or should be submitted separately to maintain focused scope.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: implementing a fix for the Tauri Error 1412 on Windows 11 by adding single-instance plugin support and window configuration adjustments.
Linked Issues check	✅ Passed	All coding requirements from issue #1147 are addressed: added tauri-plugin-single-instance dependency, implemented single-instance behavior with window focus callback, and configured window settings for Windows 11 compatibility.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[pranitaurlam]

Hi @tushar1977 @rahulharpal1603!

I've implemented a fix for issue #1147. This PR resolves the Tauri Error 1412 that causes the frontend to exit on Windows 11.

What I did:
Added tauri-plugin-single-instance to prevent multiple WebView2 instances
Configured single-instance behavior to focus existing window instead of creating duplicates
Enhanced window configuration for better lifecycle management on Windows 11

Testing needed:
Since I don't have access to a Windows 11 environment, I'd appreciate if this could be tested on Windows 11 to confirm:
The window stays open and doesn't auto-close
No Error 1412 appears in the terminal
Backend services connect successfully
Launching a second instance focuses the first window instead of crashing

The changes are minimal and non-intrusive, using a standard Tauri plugin to address the root cause of the window class conflict.

Please let me know if you need any clarification or changes! 🙏

[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@frontend/src-tauri/src/main.rs`:
- Around line 193-202: Replace the panicking expect() calls inside the
tauri_plugin_single_instance::init closure with a deterministic lookup and
graceful handling: call app.get_webview_window("main") (instead of
webview_windows().values().next()) to get an Option, match or if-let on that
Option and if Some(window) call window.set_focus() and handle the Result with
map_err/log or an if let Err(e) branch instead of expect; if the window is None
or set_focus() fails, log the condition and return without panicking so the
primary instance stays running.

🧹 Nitpick comments (1)

frontend/src-tauri/tauri.conf.json (1)

51-54: Pre-existing: initial size is smaller than minimum size.

width: 800 / height: 600 are below minWidth: 1280 / minHeight: 720. Tauri will clamp the window to the minimum, making the width/height values misleading. Not introduced by this PR, but worth a follow-up cleanup.

[tushar1977]

Hi @pranitaurlam , can you attach a video before and after the change?