Failure to start Custom DevTools prompts to try again and activates pub version

[DanTup]

[11:52:08] [DevTools] [Error] Unhandled exception:
Exception: Something went wrong while running `tool/build_release.sh.
#0      main (file:///Users/danny/Dev/Google/devtools/tool/build_e2e.dart:44:5)
<asynchronous suspension>
[11:52:08] [General] [Error] Dart DevTools exited with code 255.
[11:52:42] [General] [Info] Returning cached results for project search
[11:52:44] [General] [Info] Spawning /Users/danny/Dev/Google/flutter/bin/cache/dart-sdk/bin/dart with args ["pub","global","activate","devtools"]

Something went wrong running custom DevTools (I'll investigate that separately). This showed a prompt asking if I wanted to try again, which then triggered the pub-activate mechanism. This should not happen, the pub version is only for old SDKs.