THREADSAFE=0 was correct when sx had no threads; with std.thread (S6)
and std.http's pooled dispatch (S7b), concurrent connections corrupted
sqlite's unprotected globals (caught live: distd under ab -c20 died
with free-of-unallocated inside yy_reduce). Serialized mode is
sqlite's own default and safe for every consumer; per-connection use
across threads is the supported pattern.
The vendored amalgamation (3.53.2, public domain) plus the curated
bindings move from the distribution repo into the sx library:
'#import "vendors/sqlite/sqlite.sx"' gives any sx program SQLite
with no system dependency and no build flags — the bindings declare
the C as a named #import c unit (pinned defines + -O2), compiled
through the object cache and shadow-proof via unit-first resolution.
examples/1624 pins the version and a typed round trip in-suite.
