refactor: flatten test harness storage compat aliases (#3596)

* refactor: flatten test harness storage compat aliases

* refactor: flatten rustfs storage compat aliases (#3597)

* refactor: prune runtime storage compat surface (#3598)

* refactor: flatten runtime secondary storage compat (#3599)

* docs: add scheduler placement profiling baselines (#3600)

* feat: add observability topology capability contracts (#3601)

docs/architecture/runtime-capability-contracts.md

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+# Runtime Capability Contracts
+
+This document records the `rustfs/backlog#660` PR-08 and PR-09 contract slice.
+It adds read-only observability and topology snapshot shapes to
+`rustfs-storage-api` without coupling the contract crate to runtime, ECStore,
+admin routes, profiling, or observability implementation crates.
+
+## Observability Snapshot Contract
+
+`ObservabilitySnapshot` records:
+
+- Runtime telemetry capability state.
+- Userspace CPU and memory profiling capability state.
+- Process, system, and cgroup memory sampling state.
+- Platform support for target triple, OS, architecture, allocator, eBPF, and
+  NUMA capability.
+
+Unsupported, disabled, and unknown states are represented by `CapabilityState`
+instead of failing snapshot construction. The contract is intentionally read
+only and does not replace existing profiling routes, telemetry APIs, exporter
+pipelines, or startup behavior.
+
+## Topology Snapshot Contract
+
+`TopologySnapshot` records:
+
+- Pool, set, and disk identity indexes plus optional stable IDs.
+- Optional zone, rack, node, media, NUMA, and additional labels.
+- Topology-wide profiling, NUMA, failure-domain label, and media-label
+  capability states.
+- Per-disk media, failure-domain, NUMA, and profiling capability states.
+
+Missing labels are represented as absent `Option` values. Extra topology labels
+belong in the `additional` label map, so future inventory labels do not require
+ECStore type leakage.
+
+## Boundary Rules
+
+- No `rustfs-ecstore`, `rustfs-obs`, Axum, KMS, admin route, OTEL, eBPF, or
+  profiling implementation dependency is added to `rustfs-storage-api`.
+- No placement, membership, NUMA pinning, profiling, startup, admin route, or
+  exporter behavior changes are part of this contract slice.
+- Providers must map implementation failures into `CapabilitySnapshotError`
+  before crossing the contract boundary.