acquireFrontLease

Pins the current cache, or returns null before the first publication.

Bridge for inline readers in other modules; prefer readCurrent. Each non-null result must be passed exactly once to releaseFrontLease on this publisher in a finally block, including on failure. The cache and its arrays are borrowed, read-only, and must not escape that lease. Acquisition does not allocate a lease. Do not reenter publication while holding one. Safe from any thread.