PEGO
A220: Stream Prefix Isolation
A long-lived stream root can retain a slab containing otherwise dead early elements. Private prefix allocation isolates that root from later result chunks.
Mechanism and Invariants
Before top-level streaming starts, a negative chunk sentinel budgets 32 exact-size prefix allocations. At stream start, tails seal and the sentinel resets; later cells use normal slabs. Root protection remains necessary if growth allocates a root later. Published Nodes, lists, fields and functions stay immutable under reuse.
Scope and State
Default engine stream prefix ownership in closure and both VMs. Generated/TypeScript parsers have no stream path.
Reference Control
Build tag pego_reference_stream_prefix selects ordinary prefix slabs; combined
pego_reference_stream_storage also disables cleanup routes. The independent
tag isolates prefix ownership.
Evidence and Implementation
Record 089 measures this with undo/VM cleanup in paired retained-storage cases showing 81–92% reduction. Combined results are not prefix-only effects. It records altered inline eligibility in allocation helpers and does not claim universal throughput improvement.
Evidence records: 089.
Source owners: prefix allocation policy, nodeChunks and stream root protection.
The comparison policy distinguishes same-source controls, historical changes and full checkpoints.