Inspect & vLLM driver Features & Bugs

[jlarson4]

Description

Reviewing 4.x for additional interp relevant features that we can add to our two existing drivers

• vLLM zero-capture footgun. names = list(capture) no longer collapses () to None (which was read as "copy every buffer"). A hookless forward(return_logits=False) now skips the GPU to CPU crossing entirely on both single and batched paths.
• n_layers guard. num_hidden_layers <= 0 (or non-int) raises at boot instead of leaving a raw {I} template in the non-fireable hook set.
• weight_access flag. vLLM driver now honestly advertises weight_access (its get_param/tl_get_param RPC is what logit reconstruction already uses).
• OPT/XGLM mlp_out. SymbolicBridge.mlp.hook_in/hook_out were dead HookPoints on every boot_transformers for fc-split architectures (OPT/XGLM). Caching missed them and interventions silently no-op'd. Fixed with a permanent hook mirror in component_setup._wire_symbolic_hooks, plus Inspect-provider fc-split support (_locate_mlp) and OPT's 2-D FFN handling.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist:

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have not rewritten tests relating to key interfaces which would affect backward compatibility