Release version 1.12.3

CHANGELOG.md

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+## [1.12.3] - 2026-02-24
+
+* Stabilized Nix-based builds by switching to nixos-25.11 and committing flake.lock, ensuring reproducible pkgmgr test/runtime environments (with pip) and avoiding transient sphinx/Python 3.11 breakage.
+
+
 ## [1.12.2] - 2026-02-24
 
 * Removed infinito-sphinx package