Recover objective-event allocator reuse and terminal boundaries

RE-1040. Focused validation: cargo xtask test-group qvm-location-allocation. Machine report.

Sixteen source cases execute allocator277165 and initializer277125. First-pass reuse respects signed start+2000 and age1000 gates; a full pool retries without that age gate. Extension increments count before registration/init. Count1022 stops at diagnostics; a fully occupied1024 pool reaches fatal boundary with count1025. Initialization writes only index/in-use/class/hash/field512 sentinel and preserves other words, including free time. Native registration and terminal effects remain captured/stopped.