Unusual bug #2: while attempting to recover from #1, I added an alias on the aws.iam.User. The alias got created, and so did the renamed aws.iam.User, and now Pulumi won't start the project at all:

16:55 $ pulumi up 
Previewing update (myorg/mystack)

View Live: <https://app.pulumi.com/myorg/myproj/mystack/previews/9b6816dd>

error: unexpected duplicate resource 'mystack::myproj::myorg:myapp:MyUserResource$aws:iam/user:User::myname'