Where does the bug appear (feature/product)?
Cursor IDE
Describe the Bug
Here’s everything ready to paste:
Describe the Bug:
Cursor IDE becomes completely unresponsive when restoring Claude Code extension (anthropic.claude-code) webview tabs on startup. Terminal stops working, extensions fail to load, and settings cannot be opened. The IDE appears fully broken/corrupted but the actual cause is Cursor’s webview deserialization hanging the renderer process.
The same extension with the same sessions works perfectly in VS Code — this is a Cursor-specific bug in the webview panel restore path.
Steps to Reproduce
Install Claude Code extension (anthropic.claude-code) in Cursor
Open any project folder
Open a Claude Code session as an editor tab (not sidebar)
Close Cursor with the Claude Code tab still open
Reopen Cursor — it will attempt to restore the Claude Code tab
Terminal, extensions, and settings all stop working. Extension hosts start then exit gracefully after ~30 seconds.
Even a single Claude Code tab with a 187KB session triggers the hang. The number of tabs or session size does not matter.
Expected Behavior
Cursor should restore Claude Code webview tabs without hanging the renderer, just like VS Code does with the identical extension and data.
Operating System
Windows 10/11
Version Information
IDE:
Version: 3.0.12
VSCode Version: 1.105.1
Commit: a80ff7dfcaa45d7750f6e30be457261379c29b00
For AI issues: which model did you use?
Non model specific
Additional Information
Technical root cause analysis:
The bug is in Cursor’s registerWebviewPanelSerializer restore path for claudeVSCodePanel panels. The hang occurs before the extension’s deserializeWebviewPanel handler executes — even patching the handler to immediately call panel.dispose() does not prevent the hang.
Logs show extension hosts start normally then all exit with code 0 after ~30 seconds. Renderer log shows No Connect transport provider registered errors, indicating the shared process IPC breaks due to the renderer being blocked.
Workaround: Remove claudeVSCodePanel entries from memento/workbench.parts.editor in each workspace’s state.vscdb (located in %APPDATA%/Cursor/User/workspaceStorage//state.vscdb). Session history in ~/.claude/projects/ is unaffected — only the auto-restore tabs cause the issue.
Confirmed NOT caused by: cache corruption, bloated state.vscdb, extension conflicts, session data size, or number of open tabs. Isolated through systematic testing.
Does this stop you from using Cursor
Yes - Cursor is unusable