test_nemotron_h_scaffold goes RED on the MERGE of #784 and the #517 weight loader, though both parents are green

[localai-bot]

A clean three-way merge that does not build the behaviour either side had.

#784 (b1cd4d8f6, part of #730) rewrote the NemotronH: the unported arms REFUSE BY NAME subcase to call the REAL reg.factory->load_weights(reg, config, source) instead of downcasting a fabricated struct StubModel : vllm::LoadedModel. UBSan was right about the stub and the rewrite is correct on main, where LoadNemotronHForCausalLM reads only source.kind and the config and never touches source.safetensors.

PR #752 (row/MODEL-NEMOTRON-H-LOADER-LAND, #517 §6d) gives NemotronH a weight loader. LoadNemotronHForCausalLM now refuses an empty source by name:

Model architecture NemotronHForCausalLM: the safetensors source carries no shards

Merged, #784's ModelSource source; source.kind = kSafetensors; hits exactly that refusal, so the subcase THROWS before it ever reaches the forward:

test_nemotron_h_scaffold.cpp:666: ERROR: test case THREW exception:
  Model architecture NemotronHForCausalLM: the safetensors source carries no shards

Neither parent is red. git merge reports no conflict because the two changes touch different files. This is the [merge-tree CLEAN is not merge-tree BUILDS] class.

Repaired on row/MODEL-NEMOTRON-H-LOADER-LAND as part of the #752 review-repair, where the two sides actually meet, by splitting the subcase in two rather than deleting either side's guarantee:

• an empty safetensors source REFUSES AT LOAD, by name (NemotronHForCausalLM, carries no shards) — the guarantee moved earlier, and is asserted where it now lives;
• the forward still refuses on unmaterialized weights, reached through the exported vllm::NemotronHForward on a default-constructed NemotronHHostWeights. fix(#730): the NemotronH refusal subcase downcast a stub, so UBSan was reporting real type confusion #784's substance is kept: no StubModel, no downcast onto an object that never was a NemotronHLoadedModel, no UB.

Filed for traceability, per AGENTS.md "every change starts from an issue"; it is fixed in the same flow.