Fix cluster_api_url("mainnet") raising AttributeError

CHANGELOG.md

@@ -7,6 +7,10 @@
 - **BREAKING**: Rewrite the websocket client around a typed `Subscription` handle. `solana.rpc.websocket_api.connect()` and `SolanaWsClientProtocol` are replaced by `SolanaWsClient`, which owns its connection instead of subclassing it. Each `*_subscribe()` helper now awaits the server confirmation and returns a `Subscription`; the nine `*_unsubscribe(int)` helpers are replaced by a single `unsubscribe(subscription)`, so request IDs and server-assigned subscription IDs can no longer be confused. `recv()` and async iteration yield notifications only.
 - **BREAKING**: A `*_subscribe()`/`unsubscribe()` call whose request already reached the wire tears down the whole connection if its wait ends early — either the `request_timeout` (10s default) expiring or the awaiting task being cancelled. Every other in-flight request fails with the same exception, every `Subscription` is dropped, and the client cannot be reused. The server may have created a subscription whose ID never arrived, and an orphaned subscription cannot be cancelled without it, so the connection is dropped instead. Cancelling `recv()` is still safe, and `close()` is shielded against cancellation. See [Subscribing to Events](https://michaelhly.github.io/solana-py/cookbook/development-guides/subscribing-to-events/) for details.
 
+### Fixed
+
+- `cluster_api_url("mainnet")` raised `AttributeError: 'ClusterUrls' object has no attribute 'mainnet'`. The cluster was renamed in 0.40.2, but the lookup still used the cluster name as the field name, and the `ClusterUrls` field is `mainnet_beta`.
+
 ## [0.40.3] - 2026-08-26
 
 ### Changed

src/solana/utils/cluster.py

@@ -32,4 +32,7 @@ def cluster_api_url(cluster: Cluster | None = None, tls: bool = True) -> str:
     urls = ENDPOINT.https if tls else ENDPOINT.http
     if cluster is None:
         return urls.devnet
+    if cluster == "mainnet":
+        # The cluster was renamed to "mainnet"; the ClusterUrls field kept its old name.
+        return urls.mainnet_beta
     return getattr(urls, cluster)

tests/unit/test_cluster_api_url.py

@@ -9,3 +9,12 @@ def test_input_output():
     assert cluster_api_url("devnet") == "https://api.devnet.solana.com"
     assert cluster_api_url("devnet", True) == "https://api.devnet.solana.com"
     assert cluster_api_url("devnet", False) == "http://api.devnet.solana.com"
+    assert cluster_api_url("testnet") == "https://api.testnet.solana.com"
+    assert cluster_api_url("testnet", False) == "http://api.testnet.solana.com"
+
+
+def test_mainnet():
+    """Test that the mainnet cluster resolves to its URL."""
+    assert cluster_api_url("mainnet") == "https://api.mainnet.solana.com/"
+    assert cluster_api_url("mainnet", True) == "https://api.mainnet.solana.com/"
+    assert cluster_api_url("mainnet", False) == "http://api.mainnet.solana.com/"