build(plugin-mysql): vendor the MariaDB headers from the version the build pins

[datlechin]

The vendored MariaDB Connector/C headers and the static library we ship are different versions, and nothing keeps them together.

• Plugins/MySQLDriverPlugin/CMariaDB/include/mariadb_version.h declares MARIADB_PACKAGE_VERSION "3.4.8".
• Libs/libmariadb_arm64.a answers mysql_get_client_info() with 3.4.4, measured by a probe compiled against it.
• scripts/build-mariadb.sh pins MARIADB_VERSION="3.4.4" and builds exactly that.

So the binary is right and the headers are the wrong artifact. Their own provenance says where they came from: the vendored file carries MARIADB_PLUGINDIR "/opt/homebrew/Cellar/mariadb-connector-c/3.4.8_1/lib/mariadb/plugin". They were copied out of a Homebrew keg rather than out of the source the build script downloads.

What the skew actually contains

Diffed every vendored header against the pinned 3.4.4 source. Five differ, and two of those carry declarations the shipped binary does not export:

Header	Difference
errmsg.h	adds CR_ERR_MISSING_ERROR_INFO 5026 and moves CR_MARIADB_LAST_ERROR onto it, so the client-error boundary sits one past what the linked library can produce
mariadb_com.h	declares ma_net_write_buff and the UDF_ARGS / UDF_INIT structs
ma_tls.h	declares ma_is_ip_address
mariadb_version.h	the version macros and the Homebrew plugin directory
ma_pvio.h, mysql.h	a typo fix and two comment edits

Checked the whole surface rather than just those: of 236 function declarations across the headers, exactly two are absent from libmariadb_arm64.a, mariadb_dyncol_prepare_decimal and mariadb_load_defaults. Neither is referenced anywhere in the repo, and nor is anything else in the table above.

That makes this latent rather than active. A call to a declaration the binary lacks fails at link time, which is loud. The quiet half is a macro or a struct that changed between the two versions: it compiles, and then it is wrong.

The change

The headers now come from the 3.4.4 source that build-mariadb.sh pins. mariadb_version.h is generated by CMake rather than shipped, so it is rendered from a configure run of that same source instead of copied, which is also what drops the Homebrew path.

scripts/check-mariadb-headers.sh reads the pinned version out of build-mariadb.sh, downloads that source, renders the generated header the same way, and diffs all fifteen. It is the shape check-duckdb-value-api.sh and check-pluginkit-abi.sh already use: a fact the tree hard-codes gets a script that re-checks it, rather than a comment asking the next person to remember.

Verification

Step	Result
verify.sh build	PASS
MySQLDriver scheme	BUILD SUCCEEDED
scripts/check-mariadb-headers.sh	every vendored header matches Connector/C 3.4.4
shellcheck --severity=warning	clean

No library rebuild and no republish: the binary already is the pinned version, so Libs/ and its checksums are untouched.

Found while investigating #2427.

https://claude.ai/code/session_01KsqHrFwJxUW6eWozYjT8JZ

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