diff --git a/docs/README.md b/docs/README.md
index 388671a8..4a087bd4 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -7,6 +7,7 @@ accepted decision** when onboarding.
 
 | ADR                                                              | Topic                                                                   |
 | ---------------------------------------------------------------- | ----------------------------------------------------------------------- |
+| [0023](decisions/0023-canonical-cat-outer-puzzle-hash.md)        | **CAT outer hash** — one `coinset/cats/outer` primitive + Coinset hex   |
 | [0021](decisions/0021-three-ownership-simplifications.md)        | **Ownership spines** — expired maker, reconcile prep, `coin_ops::shape` |
 | [0020](decisions/0020-soft-expiry-stable-makers.md)              | **Soft listing expiry** — stable makers, `ensure_size_n_offer`          |
 | [0018](decisions/0018-coinset-parse-decomposition.md)            | **Coinset submodule layout** — parse, pagination, rpc_result, json_util |
diff --git a/docs/decisions/0023-canonical-cat-outer-puzzle-hash.md b/docs/decisions/0023-canonical-cat-outer-puzzle-hash.md
new file mode 100644
index 00000000..805c9420
--- /dev/null
+++ b/docs/decisions/0023-canonical-cat-outer-puzzle-hash.md
@@ -0,0 +1,50 @@
+# ADR 0023: Canonical CAT outer puzzle-hash module
+
+## Status
+
+Accepted (2026-08-10).
+
+## Context
+
+`cat(asset_id, p2)` outer puzzle hashes were computed with the same
+`CatArgs::curry_tree_hash` formula in four places:
+
+- `vault/cat_create.rs` (`receive_cat_outer_puzzle_hash`)
+- `vault_coinset_scan/cat_outer.rs` (Bytes32 + hex adapters)
+- `coinset/wallet_io.rs` (`cat_outer_puzzle_hash_hex`)
+- `coinset/cats/list.rs` (unspent CAT listing)
+
+Callers learned “how to curry,” not “give me the outer.” Hex format differences
+justified a thin Coinset adapter; the hash formula did not.
+
+## Decision
+
+One deep module owns the Bytes32 primitive:
+
+| Module                  | Responsibility                                                                     |
+| ----------------------- | ---------------------------------------------------------------------------------- |
+| `coinset/cats/outer.rs` | `cat_outer_puzzle_hash(asset, p2) → Bytes32` once; `cat_outer_coinset_hex` adapter |
+
+**Ownership split:**
+
+- **`coinset/cats/outer`** owns the curry formula and the Coinset `0x` hex adapter.
+- **`vault/cat_create`** keeps double-wrap assert policy and calls `cat_outer_puzzle_hash`
+  directly (no alias).
+- **`wallet_io` / `cats/list` / vault scan** adapt inputs (address decode, Coinset queries)
+  and call the shared primitive — they do not re-curry.
+- Bare-hex compare sites use `normalize_hex_id` on the Coinset form; there is no second
+  outer-hash helper.
+
+`vault_coinset_scan/cat_outer.rs` is deleted; scan paths import
+`crate::coinset::{cat_outer_coinset_hex, cat_outer_puzzle_hash}`.
+
+## Consequences
+
+- Outer-hash bugs and CAT puzzle upgrades localize to one module.
+- Create / scan / WS inventory / list share one `(asset, p2)` interface.
+- No behavior change: adapters preserve `0x` Coinset hex; compare paths normalize that form.
+
+## References
+
+- Architecture review 2026-08-10 (Canonical CAT outer puzzle-hash module)
+- [0018](0018-coinset-parse-decomposition.md) — Coinset submodule ownership pattern
diff --git a/docs/progress.md b/docs/progress.md
index 2c9cf038..d3dd6e28 100644
--- a/docs/progress.md
+++ b/docs/progress.md
@@ -16,6 +16,12 @@ Pre-Rust migration detail lives in git history and
 
 ## Milestones
 
+### 2026-08-10 — Canonical CAT outer puzzle-hash (ADR 0023)
+
+`cat(asset_id, p2)` outer hashes curry once in `coinset/cats/outer`; vault create-assert
+calls that primitive directly; scan / wallet_io / list use thin adapters (`cat_outer_coinset_hex`
+plus `normalize_hex_id` where bare hex is needed). Deleted shallow `vault_coinset_scan/cat_outer`.
+
 ### 2026-08-10 — Unique maker pin session deepen
 
 ADR 0022 pin protocol lives behind `UniqueMakerPinSession` (`begin` →
diff --git a/greenfloor-engine/src/coinset/cats/list.rs b/greenfloor-engine/src/coinset/cats/list.rs
index 684f412b..feb7598b 100644
--- a/greenfloor-engine/src/coinset/cats/list.rs
+++ b/greenfloor-engine/src/coinset/cats/list.rs
@@ -1,9 +1,9 @@
 use chia_protocol::Bytes32;
-use chia_puzzle_types::cat::CatArgs;
 use chia_sdk_coinset::{ChiaRpcClient, CoinRecord, CoinsetClient};
 use chia_sdk_driver::Cat;
 use futures_util::future::try_join_all;
 
+use super::outer::cat_outer_puzzle_hash;
 use super::resolve;
 use crate::bech32m::decode_address;
 use crate::coinset::pagination::coin_records_by_puzzle_hash;
@@ -17,8 +17,8 @@ pub(crate) async fn coin_records_for_cat_outer_puzzle_hash(
     asset_id: Bytes32,
 ) -> SignerResult<Vec<CoinRecord>> {
     let p2_puzzle_hash = decode_address(receive_address)?;
-    let cat_outer_puzzle_hash = CatArgs::curry_tree_hash(asset_id, p2_puzzle_hash.into()).into();
-    coin_records_by_puzzle_hash(client, cat_outer_puzzle_hash, None, None, Some(false)).await
+    let outer = cat_outer_puzzle_hash(asset_id, p2_puzzle_hash);
+    coin_records_by_puzzle_hash(client, outer, None, None, Some(false)).await
 }
 
 /// Resolve spendable [`Cat`] values with lineage proofs for coin records.
diff --git a/greenfloor-engine/src/coinset/cats/mod.rs b/greenfloor-engine/src/coinset/cats/mod.rs
index 0f82726e..41325aa4 100644
--- a/greenfloor-engine/src/coinset/cats/mod.rs
+++ b/greenfloor-engine/src/coinset/cats/mod.rs
@@ -1,8 +1,10 @@
 mod list;
+mod outer;
 mod resolve;
 
 pub(crate) use list::{coin_records_for_cat_outer_puzzle_hash, coin_records_for_coin_ids};
 pub use list::{list_unspent_cats, list_unspent_cats_by_ids};
+pub(crate) use outer::{cat_outer_coinset_hex, cat_outer_puzzle_hash};
 pub(crate) use resolve::cat_from_record;
 pub use resolve::{
     cat_child_p2_create_coin_memos, cat_from_parent_spend, child_cat_asset_ids_from_parent_spend,
diff --git a/greenfloor-engine/src/vault_coinset_scan/cat_outer.rs b/greenfloor-engine/src/coinset/cats/outer.rs
similarity index 52%
rename from greenfloor-engine/src/vault_coinset_scan/cat_outer.rs
rename to greenfloor-engine/src/coinset/cats/outer.rs
index 745680a9..3dbe5cf1 100644
--- a/greenfloor-engine/src/vault_coinset_scan/cat_outer.rs
+++ b/greenfloor-engine/src/coinset/cats/outer.rs
@@ -1,10 +1,15 @@
-//! CAT outer puzzle-hash helpers shared by discovery and prelabel.
+//! Canonical CAT outer puzzle-hash primitive.
+//!
+//! All `GreenFloor` `cat(asset_id, p2)` outer hashes go through [`cat_outer_puzzle_hash`].
+//! Coinset hex is a thin format adapter; vault double-wrap assert policy stays in
+//! `vault::cat_create`. Callers that need bare hex compare via
+//! [`crate::hex::normalize_hex_id`].
 
 use chia_protocol::Bytes32;
 use chia_puzzle_types::cat::CatArgs;
 
 use crate::coinset::to_coinset_hex;
-use crate::hex::{hex_to_bytes32, normalize_hex_id};
+use crate::hex::hex_to_bytes32;
 
 /// `cat(asset_id, p2)` outer puzzle hash.
 #[must_use]
@@ -20,26 +25,24 @@ pub(crate) fn cat_outer_coinset_hex(asset_id_hex: &str, p2_hex: &str) -> Option<
     Some(to_coinset_hex(cat_outer_puzzle_hash(asset, p2).as_ref()))
 }
 
-/// Normalized outer puzzle hash for comparing against scanned coin rows.
-#[must_use]
-pub(crate) fn cat_outer_normalized_hex(asset_id_hex: &str, p2_hex: &str) -> Option<String> {
-    let asset = hex_to_bytes32(asset_id_hex).ok()?;
-    let p2 = hex_to_bytes32(p2_hex).ok()?;
-    Some(normalize_hex_id(&hex::encode(cat_outer_puzzle_hash(
-        asset, p2,
-    ))))
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::hex::normalize_hex_id;
 
     #[test]
-    fn outer_helpers_agree_on_payload() {
+    fn coinset_hex_normalizes_to_bare_id() {
         let asset = "aa".repeat(32);
         let p2 = "11".repeat(32);
         let coinset = cat_outer_coinset_hex(&asset, &p2).expect("coinset");
-        let normalized = cat_outer_normalized_hex(&asset, &p2).expect("normalized");
-        assert_eq!(normalize_hex_id(&coinset), normalized);
+        let normalized = normalize_hex_id(&coinset);
+        assert_eq!(normalized.len(), 64);
+        assert_eq!(
+            cat_outer_puzzle_hash(
+                hex_to_bytes32(&asset).expect("asset"),
+                hex_to_bytes32(&p2).expect("p2"),
+            ),
+            hex_to_bytes32(&normalized).expect("round-trip")
+        );
     }
 }
diff --git a/greenfloor-engine/src/coinset/mod.rs b/greenfloor-engine/src/coinset/mod.rs
index 4a8c7bdb..15f37962 100644
--- a/greenfloor-engine/src/coinset/mod.rs
+++ b/greenfloor-engine/src/coinset/mod.rs
@@ -43,6 +43,7 @@ pub use cats::{
     fetch_parent_coin_spend, list_unspent_cats, list_unspent_cats_by_ids,
     require_cat_from_parent_spend,
 };
+pub(crate) use cats::{cat_outer_coinset_hex, cat_outer_puzzle_hash};
 pub use coin_select::{select_cats_smallest_first, SelectedCats, MIN_CAT_OUTPUT_MOJOS};
 pub use direct_api::{
     effective_coinset_base_url, explicit_coinset_url_override, normalize_coinset_network,
diff --git a/greenfloor-engine/src/coinset/wallet_io.rs b/greenfloor-engine/src/coinset/wallet_io.rs
index 6a2a8b84..94712c7a 100644
--- a/greenfloor-engine/src/coinset/wallet_io.rs
+++ b/greenfloor-engine/src/coinset/wallet_io.rs
@@ -2,7 +2,6 @@ use std::collections::HashSet;
 
 use crate::bech32m::{decode_address, decode_offer};
 use chia_protocol::SpendBundle;
-use chia_puzzle_types::cat::CatArgs;
 use chia_traits::Streamable;
 use serde::Serialize;
 
@@ -136,8 +135,9 @@ pub fn puzzle_hash_hex_for_receive_address(receive_address: &str) -> SignerResul
 pub fn cat_outer_puzzle_hash_hex(receive_address: &str, asset_id: &str) -> SignerResult<String> {
     let puzzle_hash = decode_address(receive_address)?;
     let asset_bytes = hex_to_bytes32(asset_id)?;
-    let cat_outer: [u8; 32] = CatArgs::curry_tree_hash(asset_bytes, puzzle_hash.into()).into();
-    Ok(to_coinset_hex(&cat_outer))
+    Ok(to_coinset_hex(
+        cats::cat_outer_puzzle_hash(asset_bytes, puzzle_hash).as_ref(),
+    ))
 }
 
 /// Inventory puzzle hashes for one market receive address (inner + optional CAT outer).
diff --git a/greenfloor-engine/src/vault/cat_create.rs b/greenfloor-engine/src/vault/cat_create.rs
index 7d4d9b28..e05bd3e7 100644
--- a/greenfloor-engine/src/vault/cat_create.rs
+++ b/greenfloor-engine/src/vault/cat_create.rs
@@ -10,17 +10,11 @@
 //! construction time; do not pass the CAT outer as the send destination.
 
 use chia_protocol::Bytes32;
-use chia_puzzle_types::cat::CatArgs;
 use chia_sdk_driver::{Cat, Outputs};
 
+use crate::coinset::cat_outer_puzzle_hash;
 use crate::error::{SignerError, SignerResult};
 
-/// Outer puzzle hash for a single-wrapped CAT on `receive_p2`.
-#[must_use]
-pub(crate) fn receive_cat_outer_puzzle_hash(asset_id: Bytes32, receive_p2: Bytes32) -> Bytes32 {
-    CatArgs::curry_tree_hash(asset_id, receive_p2.into()).into()
-}
-
 /// CAT creates recorded on a [`Outputs`] map (after `Spends::prepare`).
 pub(crate) fn created_cats(outputs: &Outputs) -> impl Iterator<Item = &Cat> {
     outputs.cats.values().flat_map(|cats| cats.iter())
@@ -41,7 +35,7 @@ pub(crate) fn assert_cat_creates<'a>(
     receive_p2: Bytes32,
     allowed_non_receive_p2s: &[Bytes32],
 ) -> SignerResult<()> {
-    let receive_outer = receive_cat_outer_puzzle_hash(asset_id, receive_p2);
+    let receive_outer = cat_outer_puzzle_hash(asset_id, receive_p2);
     for cat in cats {
         if cat.info.asset_id != asset_id {
             continue;
@@ -93,7 +87,7 @@ mod tests {
     fn rejects_outer_as_p2() {
         let asset = Bytes32::new([0xaa; 32]);
         let receive = Bytes32::new([0x11; 32]);
-        let outer = receive_cat_outer_puzzle_hash(asset, receive);
+        let outer = cat_outer_puzzle_hash(asset, receive);
         let cat = sample_cat(asset, outer, 1_000);
         let err = assert_cat_creates([&cat], asset, receive, &[]).unwrap_err();
         assert!(matches!(
diff --git a/greenfloor-engine/src/vault/mixed_split.rs b/greenfloor-engine/src/vault/mixed_split.rs
index 44499a3c..586bf591 100644
--- a/greenfloor-engine/src/vault/mixed_split.rs
+++ b/greenfloor-engine/src/vault/mixed_split.rs
@@ -285,11 +285,10 @@ mod tests {
 
     #[tokio::test]
     async fn build_mixed_split_rejects_double_wrap_and_keeps_receive_outputs() {
+        use crate::coinset::cat_outer_puzzle_hash;
         use crate::test_support::simulator::harness::SimulatorVaultHarness;
         use crate::test_support::simulator::SimulatorOfferCoinset;
-        use crate::vault::cat_create::{
-            assert_cat_creates, created_cats, receive_cat_outer_puzzle_hash,
-        };
+        use crate::vault::cat_create::{assert_cat_creates, created_cats};
         use chia_puzzle_types::Memos;
         use chia_sdk_driver::{Action, Id, SpendContext, Spends};
 
@@ -314,7 +313,7 @@ mod tests {
         assert!(!spend_bundle.coin_spends.is_empty());
 
         // Regression: Action::send to the CAT outer fails the create assert.
-        let expected_outer = receive_cat_outer_puzzle_hash(asset_id, receive_puzzle_hash);
+        let expected_outer = cat_outer_puzzle_hash(asset_id, receive_puzzle_hash);
         let mut bad_ctx = SpendContext::new();
         let mut bad_spends = Spends::new(receive_puzzle_hash);
         bad_spends.add(cat);
diff --git a/greenfloor-engine/src/vault_coinset_scan/cat_detect.rs b/greenfloor-engine/src/vault_coinset_scan/cat_detect.rs
index c1009e04..addd3529 100644
--- a/greenfloor-engine/src/vault_coinset_scan/cat_detect.rs
+++ b/greenfloor-engine/src/vault_coinset_scan/cat_detect.rs
@@ -67,11 +67,14 @@ pub fn prelabel_known_cat_outers(
     let mut outer_to_asset: HashMap<String, String> = HashMap::new();
     for asset_id in requested_cat_ids {
         for p2_hex in &inner_p2s {
-            let Some(outer) =
-                crate::vault_coinset_scan::cat_outer::cat_outer_normalized_hex(asset_id, p2_hex)
+            let Some(coinset_outer) = crate::coinset::cat_outer_coinset_hex(asset_id, p2_hex)
             else {
                 continue;
             };
+            let outer = normalize_hex_id(&coinset_outer);
+            if outer.is_empty() {
+                continue;
+            }
             outer_to_asset.insert(outer, asset_id.clone());
         }
     }
@@ -439,11 +442,13 @@ mod tests {
     fn prelabel_known_cat_outers_labels_matching_receive_outer() {
         use std::collections::{BTreeMap, HashSet};
 
-        use crate::vault_coinset_scan::cat_outer::cat_outer_normalized_hex;
+        use crate::coinset::cat_outer_coinset_hex;
+        use crate::hex::normalize_hex_id;
 
         let asset_id = "aa".repeat(32);
         let receive_p2 = "bb".repeat(32);
-        let outer = cat_outer_normalized_hex(&asset_id, &receive_p2).expect("outer");
+        let outer =
+            normalize_hex_id(&cat_outer_coinset_hex(&asset_id, &receive_p2).expect("outer"));
         let coin_id = "cc".repeat(32);
         let mut rows = HashMap::from([(
             coin_id.clone(),
diff --git a/greenfloor-engine/src/vault_coinset_scan/mod.rs b/greenfloor-engine/src/vault_coinset_scan/mod.rs
index 810f20ef..79cc659f 100644
--- a/greenfloor-engine/src/vault_coinset_scan/mod.rs
+++ b/greenfloor-engine/src/vault_coinset_scan/mod.rs
@@ -2,7 +2,6 @@
 
 pub mod asset_trace;
 pub mod cat_detect;
-pub(crate) mod cat_outer;
 pub mod checkpoint;
 pub mod cli;
 pub mod dust;
diff --git a/greenfloor-engine/src/vault_coinset_scan/state/nonce_scan.rs b/greenfloor-engine/src/vault_coinset_scan/state/nonce_scan.rs
index ae2bc033..7e0d3f7b 100644
--- a/greenfloor-engine/src/vault_coinset_scan/state/nonce_scan.rs
+++ b/greenfloor-engine/src/vault_coinset_scan/state/nonce_scan.rs
@@ -2,11 +2,11 @@ use std::collections::{HashMap, HashSet};
 
 use serde_json::Value;
 
+use crate::coinset::cat_outer_coinset_hex;
 use crate::coinset::{coin_id_from_record, to_coinset_hex, u64_from_value};
 use crate::error::SignerResult;
 use crate::hex::{hex_to_bytes32, normalize_hex_id};
 use crate::vault::members::nonce_member_puzzle_hash_hex;
-use crate::vault_coinset_scan::cat_outer::cat_outer_coinset_hex;
 use crate::vault_coinset_scan::types::{
     AssetTypeFilter, CoinKind, CoinRow, DiscoverySource, ScanStopReason,
 };
@@ -377,7 +377,7 @@ mod tests {
 
     #[tokio::test]
     async fn hint_only_discovery_skips_member_nonce_walk() {
-        use crate::vault_coinset_scan::cat_outer::cat_outer_coinset_hex;
+        use crate::coinset::cat_outer_coinset_hex;
 
         let mut server = mockito::Server::new_async().await;
         let launcher_id = "11".repeat(32);