giant predict and giant rollout each carried a ~65-line, independently
drifting copy of "load checkpoint -> validate -> resolve conditioning axes
-> restore normalizers/vocab maps -> build models -> load weights", plus a
third partial copy of _conditioning_axes in analysis/router_gating.py. A
silent divergence there doesn't crash, it makes the two commands run
different physics from the same checkpoint with no test coverage anywhere
along that path.
giant/checkpoint_io.py now holds the single implementation:
load_for_inference() + an InferenceContext dataclass, raising
CheckpointCompatibilityError (verbatim message text preserved) instead of
calling typer directly, so it can be unit-tested and imported from
non-Typer code. router_gating.py's load_router imports conditioning_axes
from it lazily, keeping its "no torch at module scope" contract intact.
Adds 17 direct unit tests for load_for_inference/conditioning_axes/stage_cfg
plus CLI smoke tests confirming the error surfaces as typer.Exit(1) through
predict and rollout — previously zero coverage on this path.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
