[Webleymkv]

I'll also cast my lot with the revolver crowd and specify a medium frame Ruger or S&W DA revolver in .38 Special or .357 Magnum with a 3-4" barrel. As for why, let's refer to the criteria:

easy to learn

Revolvers are nothing if not simple. There are no safeties to fiddle with and no need to manually chamber a cartridge in order to make the gun ready to fire. Likewise, if one wishes to verify the loaded/unloaded status of the gun all that is necessary is to open the cylinder and look at the chambers.

requires minimal complex thought...hard to forget

See the previous qualifier. DA revolvers have one of the simplest manual-of-arms available and thus have the least that can be forgotten.

easy to clean

The simplicity of a revolver again shines through here. While some semi-autos may be quite easy to disassemble and reassemble, revolvers need not be disassembled at all for normal cleaning and lubrication. Simply open the cylinder, unload the gun if necessary, clean the bore and chambers, wipe the gun down with oil (not necessary with a stainless gun) and you're done.

runs dirty

Unless the gun is grossly out of spec or has been shot with copious amounts (as in hundreds of rounds) of very dirty ammunition without being cleaned, revolvers very seldom malfunction from being dirty.

reliable OOTB and after 1000 rounds with no parts changes

Unless the gun is subjected to a quality control issue or damage from an outside force (such as a sight blade getting bent or broken because the gun was dropped), good quality revolvers can typically run just fine for decades and thousands of rounds without any parts (including springs) needing replaced. Also, the only "break in" period normally encountered on DA revolvers is that some have their triggers smooth out a bit with use.

paper plate at 25 yards accurate

The fixed barrel of a revolver makes them inherently accurate. 1" groups at 25 yards with ammo that the gun likes is not particularly rare.

easy to shoot fast doubles on that same plate at 7 yards

So long as the gun and grips match the shooter and the ammo doesn't create an excessive amount of recoil, this isn't unattainable. Part of the beauty of a revolver is that the shape and size of the grip is more customizable than that of a semi-auto because it is not constrained by the size and shape of the magazine. The DA trigger does present a bit more difficulty than a SA semi-auto trigger, but with good instruction and practice that difficulty is in no way insurmountable.

drop safe...not CA test, but in practice

Both Ruger and S&W revolvers have built in features that make them drop safe (transfer bar on Rugers and sliding hammer block on S&W). Neither gun is going to go off by itself when dropped.

meaningful SD or HD caliber

.38 Special is a perfectly adequate self-defense cartridge and .357 Magnum even more so. There is a wide variety of good hollowpoint ammunition for both cartridges and ammunition for either can be found at nearly any establishment that sells handgun ammunition.

could be CCW'd

While certainly not a pocket gun, a 3-4" barrel medium frame revolver isn't particularly difficult to carry IWB, OWB, or in a shoulder holster.

popular enough to never worry about parts, finding a gunsmith, etc.

Both S&W and Ruger have been in the DA revolver business for a long time and both have sold millions of revolvers. Common parts (both factory and aftermarket) can easily be found from usual suppliers like Brownells, Numrich, and Midway. Also, just about any competent gunsmith can work on a Ruger or S&W DA revolver.