Start SCHISM from the hotstart.nc the boundary conditions write

[rafa-guedes]

With boundary_conditions.hotstart_config enabled, hotstart.nc was written but param.nml kept ihot = 0, so SCHISM cold-started and ignored the file. SCHISMConfig.check_hotstart still looked for data.hotstart, which no longer exists: hotstart generation moved into boundary_conditions.hotstart_config.

Changes

• check_hotstart now looks at data.boundary_conditions.hotstart_config.
• When the hotstart is enabled and opt.ihot is not set, it is set to 1: SCHISM starts from the hotstart state with its clock at zero.
• An ihot of 1 or 2 set by the user is kept.
• An explicit ihot = 0 together with a hotstart is an error, because SCHISM would ignore the file.
• docs/hotstart.md explains ihot.

Checks

New tests in tests/unit/test_hotstart_ihot.py. The full suite passes.

[tomdurrant]

Correctness finding: with hotstart_config.enabled=True and nml=NML() (or a Param with opt=None), check_hotstart() returns without setting ihot. NML.update_times() later creates a Param whose ihot remains 0, so SCHISM ignores the generated hotstart. Please reject this unsupported configuration or create/set the required Param/Opt, and add a regression test.

[tomdurrant]

Follow-up: fixed in commit 17129b9. Hotstart-enabled configs now create missing NML/Param/Opt groups before setting ihot=1; added absent-group regressions. Targeted tests pass (7 passed); CI is passing.