feat(datafusion): organize Cargo.toml and clarify IPCStreamWriter codec contract

- Cleaned up alphabetical ordering in Cargo.toml.
- Added comments to clarify feature-only dependencies related to IPCStreamWriter in spill/mod.rs.
- Documented codec contract requirement in IPCStreamWriter::new for better understanding of feature dependencies.

Author: kosiew

Cargo.lock

@@ -49,6 +49,13 @@ name = "datafusion_physical_plan"
 [dependencies]
 arrow = { workspace = true }
 arrow-data = { workspace = true }
+# Feature-only dep (arrow re-exports this crate as `arrow::ipc`): lz4 and zstd
+# codec support required by IPCStreamWriter in spill/mod.rs. These features must
+# stay in sync with the SpillCompression variants in datafusion-common. Declaring
+# the dependency here makes the contract explicit and local to the crate that owns
+# spill, preventing silent regressions if workspace-level arrow-ipc features are
+# narrowed (see commit 14c18ece4 for a prior regression caused by this coupling).
+arrow-ipc = { workspace = true, features = ["lz4", "zstd"] }
 arrow-ord = { workspace = true }
 arrow-schema = { workspace = true }
 async-trait = { workspace = true }

datafusion/physical-plan/Cargo.toml

@@ -290,6 +290,16 @@ struct IPCStreamWriter {
 
 impl IPCStreamWriter {
     /// Create new writer
+    ///
+    /// # Codec contract
+    ///
+    /// `arrow-ipc` must be compiled with the `lz4` and `zstd` features
+    /// (declared explicitly in `datafusion-physical-plan/Cargo.toml`). If
+    /// those features are absent, `try_with_compression` will return an
+    /// error at runtime for [`SpillCompression::Lz4Frame`] and
+    /// [`SpillCompression::Zstd`] variants. The Cargo dependency keeps this
+    /// contract local and compiler-visible rather than relying solely on
+    /// workspace-level feature unification.
     pub fn new(
         path: &Path,
         schema: &Schema,