From 9ea70a52c7574f17986cd0966aeb87529303c856 Mon Sep 17 00:00:00 2001
From: Rodrigo Quelhas <rodrigo_quelhas@outlook.pt>
Date: Mon, 18 May 2026 21:40:10 +0100
Subject: [PATCH 1/2] Wire SubstrateConfigBuilder::set_genesis_hash through to
 Config::genesis_hash

`SubstrateConfigBuilder::set_genesis_hash` stored the value on the
builder, but `build()` did not propagate it to `SubstrateConfigInner`,
and `impl Config for SubstrateConfig` never overrode `genesis_hash()`,
falling back to the trait default of `None`.

As a result, offline workflows that rely on the configured genesis hash
(e.g. `OfflineClient::new_with_config(...).at_block(...).tx().create_signable_offline(...)`)
fail with `ExtrinsicError::GenesisHashNotProvided` even when the user
calls `set_genesis_hash`. The online path is unaffected because the
genesis hash comes from the network and is stored on `OnlineClient`.

`PolkadotConfig` inherits the same behaviour since its
`genesis_hash()` delegates to the wrapped `SubstrateConfig`.

Add the missing wiring (one field, one impl method) and a couple of
tests covering the two paths.
---
 subxt/src/config/substrate.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/subxt/src/config/substrate.rs b/subxt/src/config/substrate.rs
index ebb8131370d..f8724dcb4aa 100644
--- a/subxt/src/config/substrate.rs
+++ b/subxt/src/config/substrate.rs
@@ -102,6 +102,7 @@ impl SubstrateConfigBuilder {
                 legacy_types: self.legacy_types,
                 spec_and_transaction_version_for_block_number: self
                     .spec_and_transaction_version_for_block_number,
+                genesis_hash: self.genesis_hash,
                 metadata_for_spec_version: self.metadata_for_spec_version,
             }),
         }
@@ -132,6 +133,7 @@ pub struct SubstrateConfig {
 struct SubstrateConfigInner {
     legacy_types: Option<ChainTypeRegistry>,
     spec_and_transaction_version_for_block_number: RangeMap<u64, (u32, u32)>,
+    genesis_hash: Option<H256>,
     metadata_for_spec_version: RwLock<HashMap<u32, ArcMetadata>>,
 }
 
@@ -191,6 +193,10 @@ impl Config for SubstrateConfig {
             .cloned()
     }
 
+    fn genesis_hash(&self) -> Option<H256> {
+        self.inner.genesis_hash
+    }
+
     fn set_metadata_for_spec_version(&self, spec_version: u32, metadata: ArcMetadata) {
         self.inner
             .metadata_for_spec_version
@@ -558,4 +564,17 @@ mod test {
             serde_json::from_str(numeric_block_number_json).expect("valid block header");
         assert_eq!(header.number(), 4);
     }
+
+    #[test]
+    fn builder_propagates_genesis_hash() {
+        let hash = H256::from([42u8; 32]);
+        let config = SubstrateConfig::builder().set_genesis_hash(hash).build();
+        assert_eq!(<SubstrateConfig as Config>::genesis_hash(&config), Some(hash));
+    }
+
+    #[test]
+    fn builder_without_genesis_hash_returns_none() {
+        let config = SubstrateConfig::builder().build();
+        assert_eq!(<SubstrateConfig as Config>::genesis_hash(&config), None);
+    }
 }

From 408826a4a5bc13372101cbedd03444c5c2e71431 Mon Sep 17 00:00:00 2001
From: Rodrigo Quelhas <rodrigo_quelhas@outlook.pt>
Date: Mon, 18 May 2026 22:10:44 +0100
Subject: [PATCH 2/2] Import HashFor instead of qualifying with super::

---
 subxt/src/config/substrate.rs | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/subxt/src/config/substrate.rs b/subxt/src/config/substrate.rs
index f8724dcb4aa..a7c791753a0 100644
--- a/subxt/src/config/substrate.rs
+++ b/subxt/src/config/substrate.rs
@@ -4,7 +4,9 @@
 
 //! Substrate specific configuration
 
-use super::{Config, DefaultExtrinsicParamsBuilder, DefaultTransactionExtensions, Hasher, Header};
+use super::{
+    Config, DefaultExtrinsicParamsBuilder, DefaultTransactionExtensions, HashFor, Hasher, Header,
+};
 use crate::config::Hash;
 use crate::metadata::{ArcMetadata, Metadata};
 use crate::utils::RangeMap;
@@ -193,7 +195,7 @@ impl Config for SubstrateConfig {
             .cloned()
     }
 
-    fn genesis_hash(&self) -> Option<H256> {
+    fn genesis_hash(&self) -> Option<HashFor<Self>> {
         self.inner.genesis_hash
     }
 
@@ -569,7 +571,10 @@ mod test {
     fn builder_propagates_genesis_hash() {
         let hash = H256::from([42u8; 32]);
         let config = SubstrateConfig::builder().set_genesis_hash(hash).build();
-        assert_eq!(<SubstrateConfig as Config>::genesis_hash(&config), Some(hash));
+        assert_eq!(
+            <SubstrateConfig as Config>::genesis_hash(&config),
+            Some(hash)
+        );
     }
 
     #[test]