session-telemetry-otel owns the identity as its own module (src/user-id.ts):
getOrCreateAnonymousUserId() returns the bare UUID line in $DSH_HOME/.userid,
minting a random UUID v4 on first use — synchronous IO with a process-lifetime
memo keyed by resolved path, an exclusive-create (wx) settle for concurrent
first launches, best-effort on read-only homes, and deletion resetting the
identity on the next launch by design.
The backend carries the id as the Resource's user.id (the OTel semconv user
attribute), once per export batch alongside service.name/service.version.
The identity belongs to the OTel feed alone; the dsh-sdk launcher telemetry
keeps its own separate store.
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