paras pallet - add new extrinsincs for authorize/apply set_current_code

[bkontur]

Relates to: #5588 (comment)

Context

As a part of D-Day scenario, when governance systems are migrated to the AssetHub/Collectives. If a parachain (AssetHub or Collectives) stalls, recovery currently requires issuing paras::force_set_current_code(para_id, new_code) on the relay chain, e.g.:

// from Collectives to rescue AssetHub
pallet_xcm::send(relaychain, Transact(paras::force_set_current_code(1000, new_ah_code)))

// from AssetHub to rescue Collectives
pallet_xcm::send(relaychain, Transact(paras::force_set_current_code(1002, new_ah_code)))

However, there’s a major limitation:

• paras::force_set_current_code requires sending the entire runtime binary via XCM.
• The current max upward message size on the Collectives (parachainSystem.hostConfiguration.maxUpwardMessageSize = 65,531) is too small.
• Example: penpal_runtime.compact.compressed.wasm = 1,299,474 bytes, which far exceeds the limit.

Solution

To avoid sending the entire runtime wasm code, we can split the process off-chain:

1. New Extrinsic: paras::authorize_force_set_current_code_hash(para_id, code_hash)

   • Only callable by governance (Root).
   • Stores the approved code hash on the relay chain.

2. New Extrinsic: paras::apply_authorized_force_set_current_code(para_id, code)

   • Open for anyone to call (no origin check).
   • Checks if code matches the pre-approved hash before applying the upgrade.
   • If code matches the stored code_hash, the relay chain executes force_set_current_code(para, code).

This aligns with @rphmeier’s suggestion in this comment.