Found the hot and cold water supply valves to the washer. They were both in the off position. I turned both on, ran a test rinse, and INSTANT FLOODING!
Turned both off, realized it was the hot water that was leaking, dried up the mess as best we could, and after soaking four bath towels, cautiously turned only the cold back on and tested again. There's a bit of drippage (started at once every 5 seconds then gradually slowed to beyond 6 minutes) from the back of the hose collar, but everything seems to be working.
Used the cellphone camera to look further into the cavity and saw why the hot line was leaking... there's nothing connected to it! It's just capped. So... thanks, Thor, for that feature?
Anyway, time to button the inner- and sub-pantry walls up again, and hope the dripping is minimal or over I guess.