What the bug is

At rust/lance-io/src/object_store.rs:64, the constant DEFAULT_CLOUD_BLOCK_SIZE is defined under the cfg gate:

#[cfg(any(feature = "aws", feature = "gcp", feature = "azure", feature = "tos"))]
const DEFAULT_CLOUD_BLOCK_SIZE: usize = 64 * 1024;

However, three other provider modules also import and use this constant from their new_store implementations:

• rust/lance-io/src/object_store/providers/oss.rs:14 (use crate::object_store::{..., DEFAULT_CLOUD_BLOCK_SIZE, ...}), used at line ~108 as params.block_size.unwrap_or(DEFAULT_CLOUD_BLOCK_SIZE).
• rust/lance-io/src/object_store/providers/tencent.rs:12, used at line ~23.
• rust/lance-io/src/object_store/providers/huggingface.rs:16, used at line ~179.

Each of these provider modules is itself gated on its own feature in providers.rs (#[cfg(feature = "oss")] pub mod oss; etc.).

Why existing code doesn'''t prevent it

In CI and default builds, aws, gcp, or azure is almost always enabled, which keeps DEFAULT_CLOUD_BLOCK_SIZE defined and masks the issue. The cfg gate intersection becomes vacuous: in practice, anyone using oss/tencent/huggingface is also using one of the gated features.

Step-by-step proof

1. Edit rust/lance-io/Cargo.toml to remove the default of ["aws", "azure", "gcp"] or simply run with --no-default-features.
2. Run: cargo check --no-default-features --features oss in rust/lance-io.
3. Compilation fails with error[E0432]: unresolved import crate::object_store::DEFAULT_CLOUD_BLOCK_SIZE. The compiler points at providers/oss.rs:14 (the use site) and the cfg-disabled definition at object_store.rs:64.
4. The same failure occurs with --features tencent and --features huggingface.

Impact

Anyone packaging Lance with a minimal feature set — for instance, only oss to support Alibaba Cloud users, or only huggingface for HF integrations — will hit a hard build failure. This is exactly the kind of compile-time matrix gap that the cfg system is meant to prevent.

How to fix

Extend the cfg list to include the other three opendal-based features that already use the constant:

#[cfg(any(
    feature = "aws",
    feature = "gcp",
    feature = "azure",
    feature = "oss",
    feature = "tencent",
    feature = "huggingface",
    feature = "tos",
))]
const DEFAULT_CLOUD_BLOCK_SIZE: usize = 64 * 1024;

Severity rationale

This is pre-existing — oss, tencent, and huggingface were already omitted from the gate before this PR. The PR only added tos. However, since the PR touches this exact line and copies the same incomplete pattern (adding tos but missing the other three opendal providers), it'''s a natural opportunity to fix in passing.