Feat/account mapping chain namespaces

frame/account-mapping/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "pallet-account-mapping"
-version = "0.1.0"
+version = "0.2.0"
 license = "Apache-2.0"
 description = "Stateful mapping between Substrate AccountId32 and EVM H160 addresses, with alias registration and multichain identity support."
 authors = { workspace = true }

frame/account-mapping/src/lib.rs

@@ -367,6 +367,9 @@ pub mod pallet {
 		CommitmentMismatch,
 		/// The ZK proof for a private link dispatch is invalid.
 		InvalidProof,
+		/// Attempted to register a Substrate-native signature scheme as a chain link scheme.
+		/// Chain links are exclusively for external, non-Substrate ecosystems.
+		SubstrateNativeSchemeNotAllowed,
 	}
 
 	// ──────────────────────────────────────────────
@@ -386,6 +389,14 @@ pub mod pallet {
 			scheme: SignatureScheme,
 		) -> DispatchResult {
 			ensure_root(origin)?;
+			// Chain links are exclusively for external, non-Substrate-native ecosystems.
+			// Substrate accounts are already self-proving via their AccountId32; linking
+			// them with a chain link is meaningless and would create a confusing identity
+			// model. See SignatureScheme::is_for_external_chain() for the invariant.
+			ensure!(
+				scheme.is_for_external_chain(),
+				Error::<T>::SubstrateNativeSchemeNotAllowed
+			);
 			SupportedChains::<T>::insert(chain_id, scheme.clone());
 			Self::deposit_event(Event::SupportedChainAdded { chain_id, scheme });
 			Ok(())

frame/account-mapping/src/types.rs

@@ -12,7 +12,24 @@ pub const MAX_WHITELIST_SIZE: u32 = 20;
 /// Maximum length for metadata strings (bio, avatar CID, etc.).
 pub const MAX_METADATA_LEN: u32 = 128;
 
+/// Opaque chain identifier used as storage key for cross-chain links.
+///
+/// The `u32` namespace is split into two ranges using the high bit (bit 31):
+///
+/// | Bit 31 | Range | Standard | Examples |
+/// |--------|-------|----------|---------|
+/// | `0` | `0x0000_0000 – 0x7FFF_FFFF` | EIP-155 (EVM chain IDs) | Ethereum = 1, Polygon = 137 |
+/// | `1` | `0x8000_0000 – 0xFFFF_FFFF` | SLIP-0044 (HD wallet coin types) | Bitcoin = `0x8000_0000`, Solana = `0x8000_01F5` |
+///
+/// Use `SLIP0044_NAMESPACE | <coin_type>` to build SLIP-0044 identifiers.
+/// Canonical constants for well-known chains are defined in `protocol-core`.
+/// Governance MUST follow this convention when registering chains via `add_supported_chain`.
 pub type ChainId = u32;
+
+/// Bitmask to set bit 31, placing a coin type in the SLIP-0044 namespace.
+/// Example: `SLIP0044_NAMESPACE | 0` = Bitcoin, `SLIP0044_NAMESPACE | 501` = Solana.
+pub const SLIP0044_NAMESPACE: u32 = 0x8000_0000;
+
 pub type ExternalAddr = BoundedVec<u8, ConstU32<MAX_EXTERNAL_ADDR_LEN>>;
 
 #[derive(
@@ -27,13 +44,35 @@ pub type ExternalAddr = BoundedVec<u8, ConstU32<MAX_EXTERNAL_ADDR_LEN>>;
 	scale_codec::DecodeWithMemTracking
 )]
 #[cfg_attr(feature = "std", derive(serde::Serialize, serde::Deserialize))]
+/// Signature verification scheme used to prove ownership of a cross-chain wallet.
+///
+/// # Design invariant
+///
+/// Every variant MUST represent an **external, non-Substrate-native** signing scheme.
+/// Substrate-native schemes (Sr25519, Ed25519-Substrate, etc.) MUST NOT be added here
+/// because an `AccountId32` is already self-proving in the Substrate key model — no
+/// cross-chain proof of ownership is required or meaningful. `add_supported_chain`
+/// enforces this invariant at the governance call level via `is_for_external_chain()`.
 pub enum SignatureScheme {
 	/// Ethereum-style EIP-191 (ECDSA over Keccak256).
 	Eip191,
-	/// Solana-style Ed25519 (raw signature of the message).
+	/// Solana-style raw Ed25519 (not the Substrate Ed25519 wrapper).
 	Ed25519,
 }
 
+impl SignatureScheme {
+	/// Returns `true` if this scheme belongs to a non-Substrate-native ecosystem.
+	///
+	/// All current variants are external. Any future variant for a Substrate-native
+	/// scheme MUST return `false` here so that `add_supported_chain` rejects it.
+	pub fn is_for_external_chain(&self) -> bool {
+		match self {
+			SignatureScheme::Eip191 => true,
+			SignatureScheme::Ed25519 => true,
+		}
+	}
+}
+
 #[derive(
 	Encode,
 	Decode,