You'll notice
Useful3 Signal2
Reusing a session ID now exits with a machine-readable session_in_use code for SDK callers.
What's wrong with this entry?
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session_in_use
What
Starting with a session ID that is already in use now exits with the machine-readable code session_in_use alongside the message, so SDK and wrapper callers can tell this apart from other startup failures. The message you see is unchanged.
Evidence
session_in_use
Strings lifted out of the shipped bundle, so the claim above can be checked against them.