A browser that died between two tests left the next one only
'Target page, context or browser has been closed': Playwright logs a
browser's stderr and exit only on the pw:browser debug channel, which CI
leaves off. Each worker now keeps that channel as a bounded tail, prints
one pm-browser-exit| line on an abnormal exit and attaches the tail as
browser-stderr.txt to a test that fails on a closed or crashed target.
Nothing is retried or hidden.
Refs #513
Vito
75cd9c6e13