gateway.status.acquire_scoped_lock returns (acquired, existing_record). The irc, line and
buzz adapters tested `if not acquire_scoped_lock(...)`, and a non-empty tuple is always
truthy, so two profiles could drive one IRC nick / LINE channel / Buzz identity in
parallel. Route the three through BasePlatformAdapter._acquire_platform_lock (the seam
the other 8 adapters use), which unpacks the tuple, names the owning profile + PID in the
fatal error and honours the `--replace` takeover. Release goes through
_release_platform_lock; the private _lock_key bookkeeping is gone.
Error code changes from `lock_conflict` to `{scope}_lock` — both families are already
matched by gateway.restart.is_global_startup_conflict.
The buzz test mocked acquire_scoped_lock as a bare False, which masked the bug; it now
returns the real (False, record) contract, and irc/line gain the same conflict test.
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