Observability ECStore Dependency Inventory

This inventory closes the first rustfs/backlog#735 step: make every observability dependency on ECStore visible before introducing traits or moving dependency direction.

No behavior or crate movement is planned in inventory PRs. The current boundary is crates/obs/src/metrics/storage_api.rs; all direct rustfs_ecstore and rustfs_storage_api source references in rustfs-obs must stay in that file until the contracts below are extracted.

Dependency Inventory

Current symbol in crates/obs/src/metrics/storage_api.rs	Consumed by	Classification	Purpose
rustfs_ecstore::api::storage::ECStore as ObsStore	stats_collector.rs	Type dependency	Concrete object-store handle used to call storage admin methods and data-usage loaders.
rustfs_storage_api::{BucketOperations, BucketOptions, StorageAdminApi}	stats_collector.rs	Type and trait dependency	Method-resolution and associated type contracts for bucket listing, backend info, and storage info.
rustfs_ecstore::api::runtime::object_store_handle	stats_collector.rs	Runtime dependency	Resolves the currently published object-store handle for metric collection.
rustfs_ecstore::api::data_usage::load_data_usage_from_backend	stats_collector.rs	Behavior dependency	Loads bucket/object usage and is projected into obs-local DTOs before collectors consume it.
rustfs_ecstore::api::capacity::{get_total_usable_capacity, get_total_usable_capacity_free}	stats_collector.rs	Behavior dependency	Computes usable and free capacity from ECStore storage info.
rustfs_ecstore::api::bucket::metadata_sys::get_quota_config	stats_collector.rs	Behavior dependency	Reads per-bucket quota limits used in bucket usage metrics.
rustfs_ecstore::api::bucket::bandwidth::monitor::Monitor	runtime_sources.rs, stats_collector.rs	Type and runtime dependency	Reads replication bandwidth reports from the global bucket monitor handle.
rustfs_ecstore::api::runtime::bucket_monitor	runtime_sources.rs	Runtime dependency	Resolves the global bucket bandwidth monitor for metric collection.
rustfs_ecstore::api::bucket::replication::get_global_replication_stats	storage_api.rs snapshot helpers	Runtime dependency	Reads replication status, transfer, failure, and site-replication stats, then projects them into obs-local snapshot DTOs.
rustfs_ecstore::api::bucket::lifecycle::bucket_lifecycle_ops::{GLOBAL_ExpiryState, GLOBAL_TransitionState}	runtime_sources.rs, stats_collector.rs	Runtime dependency	Reads lifecycle expiry and transition queue counters.
rustfs_ecstore::api::error::Result as ObsEcstoreResult	stats_collector.rs	Type dependency	Preserves ECStore error propagation while data-usage behavior remains ECStore-owned.

Classification

The remaining coupling is not just a dependency declaration problem:

• type coupling: ObsStore, ObsEcstoreResult, ObsBucketBandwidthMonitor, StorageAdminApi, BucketOperations, and BucketOptions;
• runtime handle coupling: object-store handle, bucket monitor, replication stats inside snapshot helpers, expiry state, and transition state;
• behavior coupling: data-usage loading, quota lookup, and capacity math.

Removing rustfs-ecstore from crates/obs/Cargo.toml is unsafe until those three categories have replacement contracts and compile coverage.

Extraction Plan

1. Keep all direct ECStore and storage-api imports centralized in crates/obs/src/metrics/storage_api.rs.
2. Keep projecting ECStore data-usage and replication stats output into obs-local DTOs before collectors consume it.
3. Introduce obs-owned provider traits for storage info, bucket info, quota, data usage, replication, bandwidth, and lifecycle queue snapshots.
4. Implement those traits in ECStore or an ECStore-owned adapter crate after the trait shapes are covered by focused tests.
5. Remove the rustfs-ecstore dependency from rustfs-obs only after metrics behavior is unchanged through the provider traits.

Guardrails

The architecture guard enforces this inventory boundary:

• crates/obs/src/metrics/storage_api.rs is the only rustfs-obs source file allowed to reference rustfs_ecstore or rustfs_storage_api;
• raw replication stats handles and ECStore replication stat methods must stay behind the snapshot helpers in crates/obs/src/metrics/storage_api.rs;
• rustfs-obs must not add storage_compat.rs or ecstore_compat.rs passthrough bridges;
• future extraction PRs must update this inventory and the guard in the same reviewed change when a dependency category is removed.