fix(ecstore): resolve erasure parity per pool (#4801) (#5015)

* fix(ecstore): add fallible erasure construction

(cherry picked from commit bd148b20f7)

* fix(ecstore): resolve storage parity per pool

(cherry picked from commit c05c2cb24b)

* fix(ecstore): keep carved per-pool parity core self-contained on main

Fixups so the cherry-picked fallible-erasure + per-pool-parity core builds standalone on current main without the excluded scope-creep commits:
- runtime/sources.rs: re-add backend_storage_class_parities (removed by the per-pool commit; its rebalance caller was updated in an unrelated reporting commit that was left out). Reimplemented over the snapshot API, behavior-identical.
- config/mod.rs: rename the storage-class publish test module (main independently added a mod tests, so the cherry-pick collided).
- rustfs storage_api.rs + startup_storage.rs: route the storage-class ENV consts through the startup storage facade and use a local const for the erasure-set-drive-count env name, satisfying the layer/facade guardrail (main's guardrail is stricter than when the core was authored).

* fix(ecstore): use struct-init in erasure test helper to satisfy clippy field_reassign_with_default

The cherry-picked fallible-erasure commit's `erasure_with_invalid_dimensions` test helper built `Erasure` via `default()` then reassigned fields, which trips `clippy::field_reassign_with_default` under `-D warnings` (only surfaced by `--all-targets`, which lints test code). #4977 fixed this in a later commit that was not part of the carved core. Use struct-init with `..Default::default()`, matching #4977's final form.

* fix(rustfs): gate the test-only storage-class ENV facade re-export behind cfg(test)

The ENV constants (INLINE_BLOCK_ENV/OPTIMIZE_ENV/RRS_ENV/STANDARD_ENV) re-exported through the startup storage facade are only consumed by a #[cfg(test)] test in startup_storage.rs, so in a non-test lib build the re-export is unused and trips -D unused-imports under clippy --all-targets. Gate it with #[cfg(test)], matching #4977's final form.

---------

Co-authored-by: cxymds <cxymds@gmail.com>

crates/ecstore/src/runtime/sources.rs

@@ -25,7 +25,7 @@ use crate::{
     bucket::lifecycle::bucket_lifecycle_ops::{ExpiryState, TransitionState},
     bucket::metadata_sys::{BucketMetadataSys, get_global_bucket_metadata_sys},
     bucket::replication::{DynReplicationPool, ReplicationStats},
-    config::{get_global_storage_class, set_global_storage_class, storageclass},
+    config::{get_global_storage_class, get_global_storage_class_snapshot, set_global_storage_class, storageclass},
     disk::{DiskAPI, DiskOption, DiskStore, new_disk},
     error::Result,
     layout::endpoints::{EndpointServerPools, SetupType},
@@ -239,23 +239,11 @@ pub(crate) fn ensure_test_rpc_secret() {
 }
 
 pub(crate) fn storage_class_parity(storage_class: Option<&str>) -> Option<usize> {
-    get_global_storage_class().and_then(|sc| sc.get_parity_for_sc(storage_class.unwrap_or_default()))
-}
-
-pub(crate) fn backend_storage_class_parities(default_standard_parity: usize) -> (Option<usize>, Option<usize>) {
-    if let Some(sc) = get_global_storage_class() {
-        let standard = sc
-            .get_parity_for_sc(storageclass::CLASS_STANDARD)
-            .or(Some(default_standard_parity));
-        let reduced_redundancy = sc.get_parity_for_sc(storageclass::RRS);
-        (standard, reduced_redundancy)
-    } else {
-        (Some(default_standard_parity), None)
-    }
+    get_global_storage_class_snapshot().get_parity_for_sc(storage_class.unwrap_or_default())
 }
 
 pub(crate) fn storage_class_should_inline(shard_size: i64, versioned: bool) -> bool {
-    get_global_storage_class().is_some_and(|sc| sc.should_inline(shard_size, versioned))
+    get_global_storage_class_snapshot().should_inline(shard_size, versioned)
 }
 
 pub(crate) fn deployment_upload_id(upload_id: &str) -> String {
@@ -330,6 +318,25 @@ pub(crate) fn storage_class_config() -> Option<storageclass::Config> {
     get_global_storage_class()
 }
 
+pub(crate) fn storage_class_config_snapshot() -> Arc<storageclass::Config> {
+    get_global_storage_class_snapshot()
+}
+
+/// Scalar STANDARD / RRS parity for backend-info reporting.
+///
+/// Retained for the rebalance/backend-info path. `get_parity_for_sc` returns
+/// `None` when the runtime config is uninitialized or (post per-pool support)
+/// when pools disagree, so STANDARD falls back to the caller's default and RRS
+/// stays `None` — matching the pre-per-pool scalar reporting.
+pub(crate) fn backend_storage_class_parities(default_standard_parity: usize) -> (Option<usize>, Option<usize>) {
+    let sc = get_global_storage_class_snapshot();
+    let standard = sc
+        .get_parity_for_sc(storageclass::CLASS_STANDARD)
+        .or(Some(default_standard_parity));
+    let reduced_redundancy = sc.get_parity_for_sc(storageclass::RRS);
+    (standard, reduced_redundancy)
+}
+
 pub(crate) fn set_storage_class_config(config: storageclass::Config) {
     set_global_storage_class(config);
 }