Unable to resolve subagent type "side-chat" for this session. The subagent was not started

Support Bug Reports
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1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

Unable to resolve subagent type “side-chat” for this session. The subagent was not started.

Request ID: b58ae343-db75-4039-8605-20d5dcdd5114
{“error”:“ERROR_BAD_REQUEST”,“details”:{“title”:“Unsupported subagent type”,“detail”:“Unable to resolve subagent type "side-chat" for this session. The subagent was not started.”,“isRetryable”:false,“additionalInfo”:{},“buttons”:,“planChoices”:},“isExpected”:true}
Unable to resolve subagent type “side-chat” for this session. The subagent was not started.
Unsupported subagent type Unable to resolve subagent type “side-chat” for this session. The subagent was not started.
NonRetriableError: Unsupported subagent type Unable to resolve subagent type “side-chat” for this session. The subagent was not started.
at GnS (vscode-file://vscode-app/Applications/Cursor.app/Contents/Resources/app/out/vs/workbench/workbench.glass.main.js:8592:131646)
at xDa (vscode-file://vscode-app/Applications/Cursor.app/Contents/Resources/app/out/vs/workbench/workbench.glass.main.js:8592:130153)
at hiS (vscode-file://vscode-app/Applications/Cursor.app/Contents/Resources/app/out/vs/workbench/workbench.glass.main.js:8593:13645)
at Object.classify (vscode-file://vscode-app/Applications/Cursor.app/Contents/Resources/app/out/vs/workbench/workbench.glass.main.js:8593:18225)
at oiS (vscode-file://vscode-app/Applications/Cursor.app/Contents/Resources/app/out/vs/workbench/workbench.glass.main.js:8593:5924)
at async jDa.run (vscode-file://vscode-app/Applications/Cursor.app/Contents/Resources/app/out/vs/workbench/workbench.glass.main.js:8593:17547)
at async Sfe.runAgentLoop (vscode-file://vscode-app/Applications/Cursor.app/Contents/Resources/app/out/vs/workbench/workbench.glass.main.js:8727:34489)
at async DKl.streamFromAgentBackend (vscode-file://vscode-app/Applications/Cursor.app/Contents/Resources/app/out/vs/workbench/workbench.glass.main.js:18901:15115)
at async DKl.getAgentStreamResponse (vscode-file://vscode-app/Applications/Cursor.app/Contents/Resources/app/out/vs/workbench/workbench.glass.main.js:18901:33366)
at async SHe._submitChatMaybeAbortCurrent (vscode-file://vscode-app/Applications/Cursor.app/Contents/Resources/app/out/vs/workbench/workbench.glass.main.js:8705:3052)

Steps to Reproduce

Create side chat from session 773a6d91-952e-4d94-b408-1ecd90432767

Operating System

MacOS

Version Information

Version: 3.17.21 (Universal)
VS Code Extension API: 1.128.0
Commit: 8f2a112cb2845a97b75fd932ea5c470579ca4060
Date: 2026-08-25T01:05:08.089Z
Layout: Agent Window
Build Type: Stable
Release Track: Default
Electron: 40.10.3
Chromium: 144.0.7559.236
Node.js: 24.15.0
V8: 14.4.258.32-electron.0
xterm.js: 6.1.0-beta.291
OS: Darwin arm64 25.5.0

Does this stop you from using Cursor

No - Cursor works, but with this issue

5

Got the same issue buddy. Did you manage to fix it?

7

Hey @i.rpsv, thanks for the report, and sorry about the trouble.

We traced this to a change on our side that began rejecting side chats. Could you try again and let us know if the issue persists?

12

After reloading the IDE, I opened a side chat again in the same session, and it worked! Thanks

Didn’t really fix it :slight_smile: Just reloaded the IDE.