doc: Revamp verifyPreconf to better match derivation

Author: linoscope

docs/permissionless-design-doc.md

@@ -313,16 +313,23 @@ PRECONFER_SLASHER_ADDRESS = ....
 
 # The currently expected preconfer
 currentPreconfer: LookaheadSlot
-# Node's canonical L2 head
-localL2Head: Block
+
+# Node's preconfed L2 head state
+# Based on `ParentState` in Rust implementation, but extended with `rawTxListHash`:
+# https://github.com/taikoxyz/taiko-mono/blob/0ca71a425ecb75bec7ed737c258f1a35362f4873/packages/taiko-client-rs/crates/driver/src/derivation/pipeline/shasta/pipeline/state.rs#L12-L13
+class ParentState:
+    header: Header             # Standard block header (hash, number, timestamp, gasLimit, coinbase, etc.)
+    anchorBlockNumber: uint256 # L1 anchor block ID
+    rawTxListHash: bytes32     # New! Hash of raw transaction list
+    ...
+
+localL2Head: ParentState
 
 # Run this function on each reception of preconf
-def verifyPreconf(# CHANGE: Function now takes rawTxList instead of full L2 block
-                  rawTxList: List[Tx],
-                  signedCommitment: SignedCommitment):
+def verifyPreconfirmation(rawTxList: List[Tx], signedCommitment: SignedCommitment):
     """
     Verifies a received preconfirmation against lookahead schedule, the signer,
-    the expected slasher, and the provided rawTxList.
+    the slasher address, and derive and execute the L2 block.
     """
 
     commitment = signedCommitment.commitment
@@ -355,15 +362,25 @@ def verifyPreconf(# CHANGE: Function now takes rawTxList instead of full L2 bloc
     # 7) Verify timestamp does not drift too far from current time
     assert abs(preconf.timestamp - now()) <= MAX_TIMESTAMP_DRIFT
 
-    # 8) Reconstruct full L2 block by adding anchor transaction
-    anchorHash = L1.getBlockHash(preconf.anchorId)
-    anchorTx = constructAnchorTx(anchorHash)
-    l2Block = executeL2Block([anchorTx] + rawTxList)
-
-    # 9) Advance local canonical chain
-    localL2Head = l2Block
-
-    # 10) Handle explicit EOP handoff
+    # 8) Derive L2 block from preconfirmation and execute it
+    # First construct block manifest from preconfirmation parameters.
+    # Block manifest in Rust implementation::
+    # https://github.com/taikoxyz/taiko-mono/blob/0ca71a425ecb75bec7ed737c258f1a35362f4873/packages/taiko-client-rs/crates/protocol/src/shasta/manifest.rs#L22-L23
+    manifest = BlockManifest(
+        anchorBlockNumber=preconf.anchorBlockNumber,
+        timestamp=preconf.timestamp,
+        gasLimit=preconf.gasLimit,
+        coinbase=preconf.coinbase,
+        transactions=rawTxList
+    )    
+    # Then process block.
+    # This validates constraints, constructs anchor tx, and executes the block.
+    # Corresponds to `process_block_manifest` in Rust implementation:
+    # https://github.com/taikoxyz/taiko-mono/blob/0ca71a425ecb75bec7ed737c258f1a35362f4873/packages/taiko-client-rs/crates/driver/src/derivation/pipeline/shasta/pipeline/payload.rs#L290
+    # Note: This function will update the `parentState` with the newly processed block.
+    processBlockManifest(manifest, parentState)
+
+    # 9) Handle explicit EOP handoff
     if preconf.eop:
         currentPreconfer = lookaheadStore.getNextPreconfer()
 
@@ -548,4 +565,4 @@ sequenceDiagram
 
 Requiring L1 validators to directly operate infrastructure for providing preconfs is undesirable, as it would increase complexity for participating validators. This additional complexity would introduce centralizing pressures not only within the L2 preconfer set but also potentially impact decentralization of the L1 validator set itself. To mitigate this, we would want to allow validators to outsource their preconfing duties, either partially or fully, analogous to "proposer-builder separation" (PBS) in L1.
 
-A more comprehensive analysis of preconf PBS will be done in an upcoming write-up.
+A more comprehensive analysis of preconf PBS will be done in an upcoming write-up.