PEGO
A210: Bounded Stream Text Snapshots
Many small stream tokens can share one immutable snapshot of loaded text instead of creating a string copy for each token.
Mechanism and Invariants
A cache miss may snapshot a range of at most 1,024 positions when at least 64 positions are loaded. It never reads the reader. Empty ranges return empty text; oversized or undersized-loaded ranges copy. CodePoints snapshots preserve U+FFFD normalization and offset mapping; Bytes preserves raw bytes. Returned strings remain valid after compaction and retain at most one bounded snapshot, up to 4,096 bytes.
Scope and State
Default eligible stream text in closure and both VMs only. Batch substring sharing is a different input path.
Reference Control
Build tag pego_reference_stream_text selects copying. Both same-source
variants retain the input cache fields, so parent comparisons also include their
layout cost.
Evidence and Implementation
Record 088 measures large CSV allocations falling by about 97%, with workload-specific timing benefits. Small recursive-VM CodePoints streams cost about 3% more; most small paired timing ranges overlap parity. Fewer objects do not ensure less allocated volume or faster every stream.
Evidence records: 088.
Source owners: bounded snapshot cache, copy reference,
input.text.
The comparison policy distinguishes same-source controls, historical changes and full checkpoints.