A few hours of cussing and one more of harassing nice people on IRC allow us to conclude:
FastCGI doesn't in any webserver, or really at all, never saw it do a thing. Lighty is cool, but without fastcgi it can't. apache2 mod_perl almost works, tantalizingly close. It gives Content Errors and loads to fail in good browsers, but the pages load and then mostly don't do anything useful in IE6. The standalone_httpd seems to work okay, so it's just the web front end that's misconfigured, of course. Nice to have proof at least.
And it's not undocumented. In fact there is enough documentation, and config examples -- all slightly different where not contradictory -- to make this all so much more maddening. Oh and there's a book, but it's old and mostly useless (I have it at home). It's got too many knobs and far too much "magic" configuration. But now I'm being redundant, since it's frelling Perl, tmtowtdi, for web servers and web apps. Isn't that marvelous? Can't you see my smile?
This is fucking Unix, people. The only magic should be in the database used by file(1). Anything else that works by magic is suspect and subject to immediate unlinking. Use simple explainable interfaces that you actually document and that work the same way twice. No hand waving or I'm going for the Sawzall ™.
This rant brought to you by the contrast between the working install of rt36 from debian packages versus the medieval dentistry that has not yet resulted in a working install of the new upstream version on the very same server using most of the same software. AUGH.