In rawDebugSession.ts there is an event mix-up between exiting debug adapters and exiting debuggees.

An exiting debuggee is an expected and frequent event that might be relevant for the user (especially if the exit code of the debuggee is non-zero which indicates a problem).
We could show a non-zero exit status as a notification.

An exiting debug adapter (with exit code 0) is an expected and frequent event that is not relevant for a user because it is just the normal operation of VS Code debuggers. A crashing debug adapter should be logged or even added to telemetry because we should become aware of it.
We should alert the user about a crashing DA too, but that Alert must be distinguishable from a crashing debuggee (e.g. as a modal alert). A crashing DA is a serious program error and there should be a way to report this to the author of the extension.

The mix-up is in https://github.com/Microsoft/vscode/blob/75e88b676f868eebb4e3516347f8b0c540451216/src/vs/workbench/parts/debug/electron-browser/rawDebugSession.ts#L286 and https://github.com/Microsoft/vscode/blob/75e88b676f868eebb4e3516347f8b0c540451216/src/vs/workbench/parts/debug/electron-browser/rawDebugSession.ts#L542 and https://github.com/Microsoft/vscode/blob/75e88b676f868eebb4e3516347f8b0c540451216/src/vs/workbench/parts/debug/electron-browser/rawDebugSession.ts#L520.

In line 286 all "exited" events from the DA are picked and forwarded via _onDidExitAdapter. This is wrong because an exiting debuggee is not an exiting DA (and the event passed as an argument _onDidExitAdapter has the exit code from the debuggee and not the DA).

In line 542 and 520 you even create fake DAP events to fire again via _onDidExitAdapter.

I suggest the following changes:

• rename private methods onDapServerError and onServerExit to onDebugAdapterError and onDebugAdapterExit (we do not want to continue to use the term "server")
• do not create fake DAP events and fire them with this.onDapEvent({ event: 'exit', type: 'event', seq: 0 }); in lines 520 and 542. Instead fire them directly with this._onDidExitAdapter.fire(...);.
• for the _onDidExitAdapter event do not misuse the DAP event object. Either create a new event type that is independent from DAP or use a generic event.
• for the real DAP event 'exit' create a new event emitter onDidExitDebugee analog to onDidTerminateDebugee. It could very well be that you are not actually handling this event anywhere because VS Code provides no UI for the exit code yet. But please introduce the new event emitter to make the distinction clear.