Okay. It was the valve.

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A bit more tinkering and, yes, the valve is dead.  However, I do have a valve in the basement that does work, and was able to shut the water off there.  But I need a shower before going to town, so...  I'll have to figure out a way to shut off that water flow... of see if it will fit the...  No.  What works in the old system, even if it sort of fits the new system, just doesn't quite fit, for a number of reasons.  Hmm... I'll think on it as I take a bit of a breather.  One good reason to do it is to change out that faulty valve.  The other one on the t-intersect is fine.  Using that would be fine, save that I have no way to close off the faulty branch.  Hmm... having a bit more plumbing bits and baubles around wouldn't be a bad thing.  Not a plumbing warehouse, just odds and ends for the standard sizes.  Urhm, whatever standard means, really.  What, 1/4, 2/3 and or 5/8, and 1 inch?  Something like that.  A few valves, a few caps, perhaps a few quick connects?  But there is copper and, brass or steel or iron, at least I hope they are those, fittings.  Bleh.

Yeah, I can probably tie off that hose, bend it and tie or tape it.  That should work.  Then a shower, a bit of shopping with a new store in the lineup.  It's never easy, is it.  Yeah, a few extra valves for in the future.  Maybe a bit of research before I go, so as to know if there are more durable valves.  A little extra money is worth a lot less hassle.  Unfortunately, often, more money doesn't improve chances.  I'll look.

Later.