Native Second String extension: Scala-compatible similarities and phonetics

[alexy]

Scope

Port Sem's Spark Second String into an independent native Sail extension wheel under examples/extensions/second-string. It uses the existing pysail.extensions bootstrap and DataFusion scalar Arrow FFI. All sixteen original SQL names/defaults remain, and ten configured entry points preserve the Scala DSL options. No Sail host implementation changes are included.

Reference: SemyonSinchenko/spark-second-string at a35db39fa8e9b65db2d201a45b86d11a6ca34b98. Apache-2.0 attribution includes the translated Commons Codec 1.21.0 primary Double Metaphone rules.

Verification

Published source f31c33ae01e574b146853ace4a901a3876cf5417 passes the detached package gate: Rust formatting, Clippy with warnings denied, 41 release Rust tests, Ruff, strict mypy, and 112 checks in each of local and two-process-worker Sail modes. The compiled Scala oracle contains 7,296 answers; every answer passes through foreign Arrow FFI and through shuffled Sail batches in both modes. Numeric tolerance is absolute 1e-12; phonetic strings are exact.

Runtime qualification uses the existing native release Sail host at 9f0aa7d2a50f1258544d37c05dd19b3ff3d915b3, API 1 / DataFusion 55.1.0 / Arrow 59.3.0. Host and extension identities are recorded separately.

Manual check

Build/install the release wheel as described in the package README, then start a compatible host with SAIL_EXPERIMENTAL_EXTENSIONS=1. Check:

SELECT ss_jaro_winkler('martha', 'marhta');
SELECT ss_jaccard_with_options('abc', 'abd', 2);
SELECT ss_soundex('Robert');

Expected: 0.9611111111111111, 1/3, and R163. The README also gives both native integration-test commands.

Qualification and Sem research status includes retained failed attempts and scope limits. No Spark speed comparison, Linux binary qualification, or stable ABI promise is claimed.