Snapshot full union storage rather than choosing an overlapping field. Preserve structural union source syntax independently of nominal identity so direct literal arguments materialize and share normalized specialization keys. Reject uninitialized bytes and address-bearing member layouts.
Own nonzero trailing sentinels in canonical string-backed snapshots and preserve specialization identity across computed and direct views.
Verified: bro build; bro test (296 passed); python3 tests/native.py (1026 interpreter/native comparisons at -O0/-O2, 5 native allocator programs, LLVM output and CLI errors).
Reuse canonical matches for optional presence and exact by-value payload captures across checking, lowering and compile-time selection.
Snapshot the optional-match flag before selector construction: AST additions can reallocate storage and invalidate the borrowed tree until refresh.
Verified 268 bootstrap tests and 908 interpreter/native programs at -O0 and -O2, plus native allocator, LLVM and CLI checks.
Reuse checked match selection for generic constant subjects and explicit match $(). Preserve owned captures, runtime scope and control transfers; keep ordinary calls, mutable subjects and potential runtime defaults unprobed. Update README and TODO checkpoint boundaries.
Verified: bro build; bro test (250 passed); python3 tests/native.py (555 interpreter/native comparisons at -O0/-O2, allocator, LLVM and CLI checks); direct interpreter/native constant-match smoke (42).
Preserve resolver failures on synthetic selector captures before elaborating payloads; selector bodies omit the original capture uses.
Verified bro build, bro test (250 passed), and tests/native.py (536 interpreter/native programs at -O0 and -O2, allocator, LLVM and CLI checks).
hl-valdemar