Fixes first: the model host, the host boundary and the Python frontend

Before building further, a pass over the model host, gpu-lab sessions, the WebAssembly host boundary, the dev server, the Python frontend and the JIT fixes the defects found, each with a regression test.

The round began with fixes rather than features. The GPT-Neo tokenizer skipped every merge line starting with #, not just the header, dropping eight real merges (787b73a3). A gpu-lab session accepted a float feed for a quantized input and handed the floats to the backends as block bytes, and the WebAssembly arena never gave back what sessions pinned (dfbd51bb). zipp run --bc a.js executed the script it was asked only to print (4ec0f002). On Windows the dev server served .git/config through its 8.3 short name /GIT~1/config (d80f2d91). A host object key with a lone surrogate merged two keys and dropped a value without error (a04da81a).

f2ba827d fixed the Python frontend against CPython 3.11 and PyTorch 2.11: a generator suspended inside except leaked its exception into the caller, exact ties in e and g formats rounded away from zero, argparse hung on any store_true flag, and torch.save wrote a global PyTorch cannot load. 17cb442a fixed a JIT wrap that changed results: once compiled, (a + b + 0.5) | 0 at a = 2^31-1, b = 1 gave -2147483647 instead of -2147483648.