PEGO
A200: Stream Capture Frame Reuse
An emitted stream element no longer needs its completed frame structs. Rewinding their slab prefix reuses storage for the next element.
Mechanism and Invariants
Commit clears dead frames while preserving the live top-level frame. Capture value arrays, nodes and child/field slices remain separately owned and are never reused through this operation. Root-search protection handles roots that reside in sealed or later slabs. A nil callback retains ordinary collected repetition behavior.
Scope and State
Default engine streaming in closure and both VMs. Generated parsers and TypeScript have no streaming API.
Reference Control
Build tag pego_reference_stream_frames selects the former allocation route
without a runtime selector. It is independent of text and prefix cleanup
controls.
Evidence and Implementation
Record 085 measures same-source CSV stream allocated volume falling about 12–13 MB/op on each engine; closure allocations fall from 308,050 to 306,050. Median time ratios are 0.988/0.994/1.000 and ranges overlap parity. Unicode stream cases also lower allocated volume. These results support scratch reuse, not a clear broad speedup or removal of input/capture-value copying.
Evidence records: 085.
Source owners: stream frame allocation/commit, frame reuse selection.
The comparison policy distinguishes same-source controls, historical changes and full checkpoints.