AztecProtocol · nventuro · Apr 1, 2026
@@ -2,7 +2,7 @@ use crate::protocol::{hash::poseidon2_hash_bytes, traits::{Deserialize, Empty, F
 
 #[derive(Eq, Serialize, Deserialize)]
 pub struct AuthorizationSelector {
-    // 1st 4-bytes (big-endian leftmost) of abi-encoding of an event.
+    // Low 32 bits of the poseidon2 hash of the function signature.
     inner: u32,
 }
 

@@ -2,7 +2,7 @@ use crate::protocol::{hash::poseidon2_hash_bytes, traits::{Deserialize, Empty, F
 
 #[derive(Deserialize, Eq, Serialize)]
 pub struct EventSelector {
-    // 1st 4-bytes (big-endian leftmost) of abi-encoding of an event.
+    // Low 32 bits of the poseidon2 hash of the event signature.
     inner: u32,
 }
 

@@ -137,11 +137,25 @@ pub comptime fn noinitcheck(f: FunctionDefinition) {
     }
 }
 
-/// An allow_phase_change function will allow transitioning from the non-revertible to the revertible phase during its
+/// An `allow_phase_change` function will allow transitioning from the non-revertible to the revertible phase during its
 /// execution.
 ///
 /// This is an advanced feature that is typically only required for account contract entrypoints that handle
 /// transaction fee payment.
+///
+/// ## Note Retrieval
+///
+/// When notes are read e.g. via [`crate::note::note_getter::get_notes`], a
+/// [`ConfirmedNote`](crate::note::ConfirmedNote) value is returned which includes note metadata, notably whether the
+/// note was created in a previous transaction (a settled note) or in the current one (a pending note), either in the
+/// current or previous phase. Because `allow_phase_change` functions can change phases, this metadata can be left
+/// stale, e.g. it is possible to read a pending current phase note and then change phases, resulting in the note being
+/// pending previous phase insted.
+///
+/// Such a note would be rejected by the kernels if it was tried to be nullified, as the metadata is incorrect. It is
+/// therefore important to not allow [`ConfirmedNote`](crate::note::ConfirmedNote),
+/// [`HintedNote`](crate::note::HintedNote) or [`NoteMetadata`](crate::note::note_metadata::NoteMetadata) values to
+/// cross the phase barrier caused by [`crate::context::PrivateContext::end_setup`].
 pub comptime fn allow_phase_change(f: FunctionDefinition) {
     // Marker attribute - see the comment at the top of this file
     if !is_fn_external(f) {

@@ -1,6 +1,5 @@
 use aztec::{
-    context::{PrivateContext, PublicContext},
-    history::nullifier::assert_nullifier_existed_by,
+    context::{NullifierExistenceRequest, PrivateContext, PublicContext},
     keys::getters::{get_nhk_app, get_public_keys, try_get_public_keys},
     macros::notes::custom_note,
     messages::{
@@ -216,14 +215,11 @@ impl PartialUintNote {
         // We verify that the partial note we're completing is valid (i.e. completer is correct, it uses the correct
         // state variable's storage slot, and it is internally consistent).
         let validity_commitment = self.compute_validity_commitment(completer);
-        // `assert_nullifier_existed_by` function expects the nullifier to be siloed (hashed with the address of the
-        // contract that emitted the nullifier) as it checks the value directly against the nullifier tree and all the
-        // nullifiers in the tree are siloed by the protocol.
+
         let siloed_validity_commitment = compute_siloed_nullifier(context.this_address(), validity_commitment);
-        assert_nullifier_existed_by(
-            context.get_anchor_block_header(),
-            siloed_validity_commitment,
-        );
+        // Note that this means we don't support scenarios in which the validity commitment was created in the same
+        // transaction.
+        context.assert_nullifier_exists(NullifierExistenceRequest::for_settled(siloed_validity_commitment));
 
         // We need to do two things:
         //  - emit an unencrypted log containing the public fields (the storage slot and value) via the private log

@@ -3,7 +3,7 @@ use std::meta::derive;
 
 #[derive(Deserialize, Eq, Serialize)]
 pub struct FunctionSelector {
-    // 1st 4-bytes (big-endian leftmost) of abi-encoding of an event.
+    // Low 32 bits of the poseidon2 hash of the function signature.
     pub inner: u32,
 }
 

diff --git a/yarn-project/stdlib/src/abi/selector.ts b/yarn-project/stdlib/src/abi/selector.ts
@@ -4,7 +4,7 @@ import { bufferToHex } from '@aztec/foundation/string';
 
 import { inspect } from 'util';
 
-/** A selector is the first 4 bytes of the hash of a signature. */
+/** A selector is the low 4 bytes of the poseidon2 hash of a signature. */
 export abstract class Selector {
   /** The size of the selector in bytes. */
   public static SIZE = 4;