library: vendors/sqlite — SQLite ships with sx

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.

library/vendors/sqlite/README.md

@@ -0,0 +1,40 @@
+# vendors/sqlite — SQLite for sx programs
+
+- Version: **3.53.2** (`SQLITE_VERSION` in `c/sqlite3.h`)
+- Source: <https://sqlite.org/2026/sqlite-amalgamation-3530200.zip>
+- Zip sha256: `8a310d0a16c7a90cacd4c884e70faa51c902afed2a89f63aaa0126ab83558a32`
+- Files kept: `c/sqlite3.c`, `c/sqlite3.h` (the amalgamation; `shell.c`
+  and `sqlite3ext.h` dropped — no shell, no loadable extensions)
+- License: public domain (<https://sqlite.org/copyright.html>)
+
+`#import "vendors/sqlite/sqlite.sx"` gives any sx program SQLite with
+no system dependency and no build flags. The bindings declare the
+amalgamation as a named `#import c` unit carrying the pinned compile
+options (`SQLITE_DQS=0`, `SQLITE_THREADSAFE=0`,
+`SQLITE_DEFAULT_MEMSTATUS=0`, `SQLITE_OMIT_DEPRECATED`,
+`SQLITE_OMIT_SHARED_CACHE`, `SQLITE_LIKE_DOESNT_MATCH_BLOBS`,
+`SQLITE_ENABLE_COLUMN_METADATA`, `-O2`); sx compiles the unit through
+its content-addressed object cache (`.sx-cache/`), so the 250k-line
+source builds once per machine. `sx build` links the objects into the
+binary; `sx run` loads them as a PRIORITY symbol-search target ahead
+of the process images, so an OS libsqlite3 of a different version can
+never shadow this copy. `examples/1624-vendor-sqlite-module.sx` pins
+the version and a typed round trip in the sx suite.
+
+## Bound surface
+
+`sqlite.sx` maps the full practical C API (~100 functions): connection
+lifecycle + open_v2 flags, errors (extended codes included), statements
+with the complete bind/column families, parameter and column
+introspection (built with `SQLITE_ENABLE_COLUMN_METADATA`), incremental
+blob I/O, the online backup API, serialize/deserialize, and the library
+utilities. Not bound, by design: callback-taking APIs (hooks, UDFs,
+collations, authorizers — they need C→sx callbacks), the
+`sqlite3_value_*` family (UDF-coupled), varargs configuration, UTF-16
+variants, and subsystems this build omits (mutex/VFS under
+`SQLITE_THREADSAFE=0`, sessions/snapshots/vtabs, deprecated API).
+
+To upgrade: replace `c/sqlite3.c`/`c/sqlite3.h` with a newer
+amalgamation, update this file and the version pins in consuming test
+suites, and rebuild (the object cache keys on the source bytes, so the
+new amalgamation recompiles automatically).