Profile
After #594, a fresh 100,000-job representative_temporal sample makes fixed-field duration snapshots the dominant remaining native leaf: mem.eqlBytes (240 top-of-stack samples), Shape.lookupState (202), and namedOwnDataValuesSnapshot (55). The current safe snapshot still performs one full Shape lookup per requested name, so a one-property duration literal and %Object.prototype% repeatedly walk the same immutable shallow chains.
Scope
- Add a bounded, allocation-free fixed-field snapshot primitive that scans a shallow immutable Shape chain once and classifies only the requested names.
- Preserve newest-operation/deletion semantics, accessor rejection, one-lock value publication, and the lock-free all-absent linearization point.
- Use a compile-time exact classifier so attacker-controlled names do not enter a hash shortcut or collision-prone cache.
- Fall back before observable work for deep/dictionary-shaped objects; add no unbounded or process-global cache.
Acceptance
- Tests cover present, absent, deleted/re-added, accessor, and fallback shapes.
- Focused normal and TSan gates pass with zero leaks/races.
- Core and Intl402 Temporal subtrees remain exact.
- Exact-parent base/variant measurements retain matching checksums and show a stable improvement.
- Full sharded units pass.
No-workaround rules
No immutable-user-object assumption, skipped getter, stale slot cache, hash-only name identity, unsynchronized slot read, unbounded shape cache, or changed fallback semantics.