Breaking: removes fetch-depth, filter, sparse-checkout, sparse-checkout-cone-mode
inputs. Composite always populates full history + blob:none so every caller
for the same SHA gets the same tarball. Cache key simplifies to repo-<sha>.
Rationale: every sparse callsite in cula-platform runs downstream of a
full-tree-populating job (find_affected). Full-tree restore (~3-5s) is
faster than sparse clone (~10-20s). One cache entry per SHA, no
fragmentation, no races on conflicting tarball contents.
If someone needs a sparse checkout outside the cache, use raw actions/checkout.
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