feat: improve legacy metadata and admin compatibility (#2202)

scripts/test/decommission_validation.md

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+# Decommission Validation
+
+This helper covers a practical decommission smoke flow against a disposable multi-pool cluster that is already running and reachable via `mc`.
+
+## What It Covers
+
+- Versioned object rewrite
+- Multipart object rewrite
+- Delete-marker preservation
+- Object-lock bucket readability after decommission
+- Admin decommission start/status/cancel command flow
+
+## What It Does Not Cover Automatically
+
+- Remote tier object migration
+- Lifecycle-expired object skipping
+- Replication target side-effects
+- Cross-node failure injection during decommission
+
+Those scenarios still need cluster-specific setup and should be verified manually after the smoke flow passes.
+
+## Prerequisites
+
+- `mc` installed and configured with an alias that points to the RustFS cluster
+- A disposable cluster with at least two pools
+- A pool cmdline string that matches the admin API input, for example:
+  `http://server{5...8}/disk{1...4}`
+
+## Recommended Flow
+
+1. Prepare data:
+   `./scripts/test/decommission_validation.sh prepare <alias>`
+2. Start decommission:
+   `./scripts/test/decommission_validation.sh start <alias> '<pool-cmdline>'`
+3. Wait for completion:
+   `./scripts/test/decommission_validation.sh wait <alias> '<pool-cmdline>' 900`
+4. Verify readable data and version listings:
+   `./scripts/test/decommission_validation.sh verify <alias>`
+
+## Optional Cancel Check
+
+1. Start decommission on a disposable pool.
+2. Run:
+   `./scripts/test/decommission_validation.sh cancel <alias> '<pool-cmdline>'`
+3. Confirm status shows `canceled=true` and not `complete=true`.
+
+## Manual Extension For Tiered Objects
+
+If the cluster already has a configured remote tier and ILM transition rule:
+
+1. Upload an object that matches the transition rule.
+2. Wait until the object is transitioned remotely.
+3. Run the decommission flow above.
+4. Confirm:
+   - the object is still readable after decommission
+   - decommission completes without `failed=true`
+   - no residual object/version remains on the source pool