Ditch achieved work, reduce MaxReorgDepth

pallets/qpow/src/lib.rs

@@ -26,7 +26,7 @@ pub mod pallet {
 		traits::{BuildGenesisConfig, Time},
 	};
 	use frame_system::pallet_prelude::BlockNumberFor;
-	use qpow_math::{achieved_difficulty_from_hash, get_nonce_hash, is_valid_nonce};
+	use qpow_math::{get_nonce_hash, is_valid_nonce};
 	use sp_core::U512;
 
 	pub type NonceType = [u8; 64];
@@ -306,9 +306,23 @@ pub mod pallet {
 			verify
 		}
 
-		/// Verify nonce validity and return achieved difficulty in a single call.
-		/// This avoids computing the nonce hash twice when both validation and
-		/// achieved difficulty are needed during block import.
+		/// Verify the nonce and return the block's work used for chain selection.
+		///
+		/// IMPORTANT: despite the legacy name, this returns the *target* difficulty the
+		/// block had to satisfy (the network difficulty at this height), NOT the achieved
+		/// difficulty derived from the winning hash. Target-based work matches Bitcoin
+		/// (`2^256/(target+1)`) and Ethereum PoW (sum of the `difficulty` field): every
+		/// block at a given difficulty contributes an identical, deterministic amount of
+		/// work, so cumulative chain work tracks expended hash power instead of being
+		/// dominated by a single lucky hash.
+		///
+		/// The runtime API name is intentionally left unchanged so this can ship as an
+		/// on-chain-only upgrade: because the metric is determined by the value this
+		/// returns (the client merely accumulates `parent_work + value`), upgrading the
+		/// on-chain Wasm flips the whole network to target-based work at the `set_code`
+		/// block, with no coordinated node-binary upgrade and no resync. Renaming the API
+		/// would break that compatibility, so defer the rename to a later release once all
+		/// nodes run a binary that expects the new name.
 		///
 		/// Note: This is called via runtime API from the client side. Runtime API
 		/// calls execute in a temporary context where state changes are discarded,
@@ -317,10 +331,9 @@ pub mod pallet {
 			block_hash: [u8; 32],
 			nonce: NonceType,
 		) -> (bool, U512) {
-			let (valid, _, hash_achieved) = Self::verify_nonce_internal(block_hash, nonce);
-			let achieved_difficulty =
-				if valid { achieved_difficulty_from_hash(hash_achieved) } else { U512::zero() };
-			(valid, achieved_difficulty)
+			let (valid, difficulty, _) = Self::verify_nonce_internal(block_hash, nonce);
+			let block_work = if valid { difficulty } else { U512::zero() };
+			(valid, block_work)
 		}
 
 		pub fn initial_difficulty() -> Difficulty {

pallets/qpow/src/tests.rs

@@ -285,26 +285,22 @@ fn test_verify_and_get_achieved_difficulty() {
 		let block_hash = [1u8; 32];
 		let nonce = [2u8; 64];
 
-		// Call the combined function
-		let (valid, achieved_diff) = QPow::verify_and_get_achieved_difficulty(block_hash, nonce);
+		// Despite the legacy name, this returns the target difficulty (block work).
+		let (valid, block_work) = QPow::verify_and_get_achieved_difficulty(block_hash, nonce);
 
 		// Check that verify_nonce_on_import_block returns the same validity
 		let expected_valid = QPow::verify_nonce_on_import_block(block_hash, nonce);
 		assert_eq!(valid, expected_valid, "Validity should match verify_nonce_on_import_block");
 
 		if valid {
-			let nonce_hash = QPow::get_nonce_hash(block_hash, nonce);
-			let expected_from_hash = U512::MAX / nonce_hash;
+			// Work is the target difficulty the block satisfied, NOT MAX / nonce_hash.
 			assert_eq!(
-				achieved_diff, expected_from_hash,
-				"Achieved difficulty should equal U512::MAX / nonce_hash"
+				block_work,
+				QPow::get_difficulty(),
+				"Block work should equal the target difficulty"
 			);
 		} else {
-			assert_eq!(
-				achieved_diff,
-				U512::zero(),
-				"Invalid nonce should yield zero achieved difficulty"
-			);
+			assert_eq!(block_work, U512::zero(), "Invalid nonce should yield zero work");
 		}
 	});
 }

runtime/src/configs/mod.rs

@@ -157,7 +157,7 @@ parameter_types! {
 impl pallet_qpow::Config for Runtime {
 	type InitialDifficulty = QPoWInitialDifficulty;
 	type TargetBlockTime = TargetBlockTime;
-	type MaxReorgDepth = ConstU32<180>;
+	type MaxReorgDepth = ConstU32<100>;
 	type WeightInfo = ();
 }