How to force flutter upgrade to re-run even if flutter thinks it's up-to-date

Lets say you’re running flutter upgrade and you are somewhere along in the process such as:

 97  235M   97  228M    0     0   402k      0  0:10:00  0:09:42  0:00:18 1376k
 98  235M   98  231M    0     0   405k      0  0:09:54  0:09:43  0:00:11 1734k
 98  235M   98  232M    0     0   407k      0  0:09:51  0:09:43  0:00:08 1660k
 99  235M   99  234M    0     0   409k      0  0:09:48  0:09:44  0:00:04 1545k
 99  235M   99  235M    0     0   411k      0  0:09:46  0:09:45  0:00:01 1422k
100  235M  100  235M    0     0   411k      0  0:09:46  0:09:46 --:--:-- 1779k
Building flutter tool...

Upgrading engine...
Downloading android-arm-profile/darwin-x64 tools...                 4.3s
Downloading android-arm-release/darwin-x64 tools...                 3.3s
Downloading android-arm64-profile/darwin-x64 tools...            2,381ms
Downloading android-arm64-release/darwin-x64 tools...            1,914ms
Downloading android-x64-profile/darwin-x64 tools...                 6.6s
Downloading android-x64-release/darwin-x64 tools...                 6.9s
Downloading android-x86 tools...                                   14.9s
Downloading android-x64 tools...                                    6.2s
Downloading android-arm tools...                                    6.3s

And you lose internet.

Then you regain internet access but the upgrade process doesn’t seem to be progressing, so you press ctrl-c in the terminal breaking out of the script and returning to the command line.

Then you type flutter upgrade to start the process over, but it says:

"Flutter is already up to date on channel stable…"

But this seems very fishy because you know that the process did not complete and so you suspect that your flutter installation and/or its related components may have become invisibly borked… and so you start over eating due to anxiety.

How do you force the upgrade process to start over from the beginning?