Unable to properly debug extension webviews anymore

[eamodio]

Does this issue occur when all extensions are disabled?: Yes/No

• VS Code Version: 1.106.0-insider (user setup)
  Commit: facd8c5
  Date: 2025-10-27T09:47:48.225Z
  Electron: 37.7.0
  ElectronBuildId: 12597478
  Chromium: 138.0.7204.251
  Node.js: 22.20.0
  V8: 13.8.258.32-electron.0
• OS Version: Windows_NT x64 10.0.26220

Steps to Reproduce:

1. Put a breakpoint within an extension webview
2. 🐛 VS Code debugger will stop when the breakpoint is hit, but the debugger is "hung" (except for stopping).

• Local's window just has a spinner
• Call stack appear but doesn't do anything when you interact with it

I'm not sure when this started but its been a at least a release or two.

I also opened the Output pane to the Extension Host channel and I saw:

2025-10-27 18:46:23.582 [error] SyntaxError: Unterminated string in JSON at position 262140 (line 1 column 262141)
    at JSON.parse (<anonymous>)
    at It._onMessage (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:63:7593)
    at c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:63:7103
    at L.fire (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:44:11091)
    at r.<anonymous> (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:108:30452)
    at By (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:51607)
    at r.n (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:50896)
    at r.emit (node:events:519:28)
    at qx.zY (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:65730)
    at qx.emit (node:events:519:28)
    at qx.dataMessage (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:43619)
    at qx.getData (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:42862)
    at qx.startLoop (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:39432)
    at qx._write (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:38716)
    at writeOrBuffer (node:internal/streams/writable:572:12)
    at _write (node:internal/streams/writable:501:10)
    at qx.Writable.write (node:internal/streams/writable:510:10)
    at Socket.qy (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:66450)
    at Socket.emit (node:events:519:28)
    at addChunk (node:internal/streams/readable:561:12)
    at readableAddChunkPushByteMode (node:internal/streams/readable:512:3)
    at Socket.Readable.push (node:internal/streams/readable:392:5)
    at TCP.onStreamRead (node:internal/stream_base_commons:189:23)
2025-10-27 18:54:54.749 [error] SyntaxError: Unterminated string in JSON at position 262140 (line 1 column 262141)
    at JSON.parse (<anonymous>)
    at It._onMessage (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:63:7593)
    at c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:63:7103
    at L.fire (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:44:11091)
    at r.<anonymous> (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:108:30452)
    at By (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:51607)
    at r.n (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:50896)
    at r.emit (node:events:519:28)
    at qx.zY (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:65730)
    at qx.emit (node:events:519:28)
    at qx.dataMessage (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:43619)
    at qx.getData (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:42862)
    at qx.startLoop (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:39432)
    at qx._write (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:38716)
    at writeOrBuffer (node:internal/streams/writable:572:12)
    at _write (node:internal/streams/writable:501:10)
    at qx.Writable.write (node:internal/streams/writable:510:10)
    at Socket.qy (c:\Users\eric\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\ms-vscode.js-debug\src\extension.js:12:66450)
    at Socket.emit (node:events:519:28)
    at addChunk (node:internal/streams/readable:561:12)
    at readableAddChunkPushByteMode (node:internal/streams/readable:512:3)
    at Socket.Readable.push (node:internal/streams/readable:392:5)
    at TCP.onStreamRead (node: internal/stream_base_commons:189:23)

And here is the logs from the trace on the launch config:

vscode-debugadapter-047a3de0.json

/cc @connor4312

[eamodio]

@connor4312 Any idea here?