Every intuition on the way to this one was wrong, including several of mine, so the
log records the wrong turns as well as the answer — that is the part worth reading
back.
The shape: nothing crashed. sclang up, scsynth up on 6.7% CPU, sink RUNNING,
routing intact, and no sound. Any monitor aimed at SuperCollider would have
reported a healthy rig. PLN found the discriminator himself by switching the
default sink by hand — internal speaker plays, UMC does not — which killed the
pure-CPU theory and pointed at the interface, which was also not at fault: 128
vs 1024 period_size is an 8x tighter deadline, so the UMC is the canary.
Recorded because they will recur:
- `state: RUNNING` lied while the device was dying once a second; only repeated
hw_ptr sampling is honest, and FOUR samples, not two — my two-sample read
called it "still stalling" when a ring-buffer wrap looks identical to a stall.
- a rule scoped to one device but applied to the whole graph stops being a fix
and becomes a load (52-no-suspend matched every node; two nodes nobody used
held 2.1M xruns).
- the laptop mic had auto-wired itself into the d1 stem, invisible in Ardour's
GUI and in the saved session, and Take95 is already exported (#132).
- #7 survived two fixes because the metric counted the BOUNDED map.
- my own journalctl scans burned a core twice while he was losing audio. I was
the load I was measuring.
