Review tmx port

Problem

Claude ported 15k lines. we need to review

Solution

The review of #1359 concluded that 15k lines cannot be reviewed as one PR. The answer was to split the port into pieces that can each be read on their own, each with its own datatest: the package and everything needing no operators (#1457), then one subcomponent at a time: diagnostics, scalar and momentum diffusion, energy update.

Remaining review work is: reading the pieces as they arrive.

Progress

• #1359 read by DropD, OngChia, havogt and yiluchen1066; the verdict was to split it
• #1457 the package, its configuration and static states -- merged 14.09.2026
• #1458 the prescribed surface fluxes, split out of #1457 after the review found the flux providers had no caller there
• #1475 the diagnostics stage as a component of its own
• the remaining subcomponents: scalar and momentum diffusion, energy update

This cost considerably more than the one week it was bet at.