Pallet XCM - transfer_assets pre-ahm patch

[RomarQ]

⚠️ Breaking Changes ⚠️

Pallet XCM's transfer_assets extrinsic now returns an error when it determines that a reserve transfer of DOT | KSM has to be done. This is a safeguard in preparation for the Asset Hub Migration (AHM), where the reserve of DOT | KSM will change from the Relay Chain to Asset Hub.

What does it do?

Ports paritytech/polkadot-sdk#9137

transfer_assets automatically figures out the reserve for a cross-chain transfer
based on on-chain configurations like IsReserve and the asset ids.
The Asset Hub Migration (AHM) will make it unable to return the correct reserve for
the network native asset (DOT, KSM, WND, PAS) since its reserve will move from the
Relay Chain to the Asset Hub.

Before the migration, it'll be disabled to do network native reserve transfers
via transfer_assets. After the migration, once everything is configured properly,
it'll be patched to use the correct reserve.

[coderabbitai]

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✨ Finishing Touches

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch rq/transfer-assets-fix

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[github-actions]

WASM runtime size check:

Compared to target branch

Moonbase runtime: 2420 KB (-4 KB) 🚨

Moonbeam runtime: 2572 KB (no changes) 🚨

Moonriver runtime: 2564 KB (-8 KB) 🚨

Compared to latest release (runtime-3800)

Moonbase runtime: 2420 KB (+376 KB compared to latest release) 🚨

Moonbeam runtime: 2572 KB (+408 KB compared to latest release) 🚨

Moonriver runtime: 2564 KB (+400 KB compared to latest release) 🚨

[github-actions]

Coverage Report

@@                    Coverage Diff                     @@
##           master   rq/transfer-assets-fix      +/-   ##
==========================================================
+ Coverage   74.07%                   74.17%   +0.10%     
  Files         406                      406              
+ Lines       98988                    99151     +163     
==========================================================
+ Hits        73318                    73544     +226     
- Misses      25670                    25607      -63     

Files Changed	Coverage
/pallets/erc20-xcm-bridge/src/erc20_trap.rs	68.18% (+68.18%)	🔼
/runtime/moonbase/src/weights/xcm/generic.rs	5.19% (+1.50%)	🔼
/runtime/moonbase/src/weights/xcm/mod.rs	15.79% (+3.35%)	🔼
/runtime/moonbase/tests/common/mod.rs	95.38% (+0.23%)	🔼
/runtime/moonbeam/src/weights/xcm/generic.rs	10.36% (+1.53%)	🔼
/runtime/moonbeam/src/weights/xcm/mod.rs	26.79% (+3.35%)	🔼
/runtime/moonbeam/tests/common/mod.rs	95.77% (+0.26%)	🔼
/runtime/moonbeam/tests/integration_test.rs	99.40% (+0.01%)	🔼
/runtime/moonriver/src/weights/xcm/generic.rs	9.05% (+1.51%)	🔼
/runtime/moonriver/src/weights/xcm/mod.rs	25.36% (+3.35%)	🔼
/runtime/moonriver/tests/common/mod.rs	95.85% (+0.25%)	🔼
/runtime/moonriver/tests/integration_test.rs	99.38% (+0.02%)	🔼

Coverage generated Fri Aug 29 13:09:47 UTC 2025