Add fallback for tx hash resolution by cid in claim token API

docs/api-documentation.md

@@ -16,6 +16,9 @@ transaction hash confirming the token transfer.
 
 - Each address is subject to rate limiting to prevent abuse.
 - This API only distributes Calibnet `tFIL` and `tUSDFC` tokens.
+- For native token claims, the API returns the Ethereum transaction hash if
+  resolvable via `Filecoin.EthGetTransactionHashByCid`; otherwise, it returns
+  the CID.
 
 ---
 

src/faucet/server_api.rs

@@ -309,11 +309,16 @@ async fn handle_native_claim(
     {
         Ok(LotusJson(smsg)) => {
             let cid = rpc.mpool_push(smsg).await.map_err(ServerFnError::new)?;
-            let tx_hash = rpc
+            Ok(rpc
                 .eth_get_transaction_hash_by_cid(cid)
                 .await
-                .map_err(ServerFnError::new)?;
-            Ok(tx_hash.to_string())
+                .map(|tx_hash| tx_hash.to_string())
+                .unwrap_or_else(|err| {
+                    log::warn!(
+                        "Failed to resolve tx hash for CID {cid}: {err}. Returning CID instead."
+                    );
+                    cid.to_string()
+                }))
         }
         Err(err) => Err(handle_faucet_error(err)),
     }