Copilot chat window not accessible any more because of `Unknown event type: "session.mode_changed"`

[janpio]

Version: 1.109.5 (user setup)
Commit: 0725862
Date: 2026-02-19T19:43:32.382Z
Electron: 39.3.0
ElectronBuildId: 13313481
Chromium: 142.0.7444.265
Node.js: 22.21.1
V8: 14.2.231.22-electron.0
OS: Windows_NT x64 10.0.26200

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While playing around with background agents, I got into a situation where I can not open a specific agent session any more, as I get this error and this then makes the Chat window unusable for Copilot:

Failed to open chat session: Session file is corrupted (line 170: Unknown event type: "session.mode_changed")

[janpio]

Found a way to not have to kill the running background agent session by duplicating the workspace:

In a window of the project you want to duplicate, open the command panel ( Command + Shift + P in Mac or Ctrl + Shift + P in Ubuntu), then type dupl (and select Workspaces: Duplicate As Workspace in New Window ), this will duplicate your workspace in a new window.

Note that I then have to avoid clicking the broken session, or I will be in the same state again.