Since #118246 one local `hermes serve` serves every profile, and main marks
those routes `sharedPrimary: true`. `requestGatewayForProfile` honoured the
flag, but the session-owner family (`requestGatewayForAgent`, retain/open/
ensure) went through `isAttachedSharedRemote`, whose `primaryConnectionMode
=== 'local'` early return (#113956, written while every local profile had
its own pooled child) sent every non-default local profile to a registry
secondary: a SECOND WebSocket to the SAME backend process. The backend joins
any socket that sends a session call to the chat's transport fan-out, so the
renderer received every event twice — "HelloHello from from the the mock
mock…" while streaming, duplicate interim bubbles, doubled error cards
(#120005, #119131, #119566, #119540, #118934).
The predicate is now `ridesPrimaryBackend`: it asks main for the route on
every call and reuses the primary socket (with the `profile` param) when the
descriptor carries `sharedRemote` (#96493) OR `sharedPrimary` (#118246).
#101416 stays fixed: when the probe fails on a LOCAL primary we never fall
back to the primary (a pooled profile's chat must not be minted under the
primary's pid), and a pooled descriptor (HERMES_DESKTOP_ISOLATED_BACKEND=1)
still opens its own secondary.
Closes#120006. Part of #120005.
0bb539b472