fix(wallet-sdk): narrow fee prediction fallback to method-not-found errors

Addresses PR #22116 review comment 2: the catch-all fallback could mask
RPC connectivity issues by silently falling back to getCurrentMinFees.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: spalladino

yarn-project/wallet-sdk/src/base-wallet/base_wallet.ts

@@ -262,9 +262,13 @@ export abstract class BaseWallet implements Wallet {
         return this.aztecNode.getCurrentMinFees();
       }
       return predicted.reduce((worst, fees) => (fees.feePerL2Gas > worst.feePerL2Gas ? fees : worst));
-    } catch {
-      // Fallback for old nodes that don't support getPredictedMinFees
-      return this.aztecNode.getCurrentMinFees();
+    } catch (err: any) {
+      // Fallback for old nodes that don't support getPredictedMinFees.
+      // Only fall back on method-not-found errors (JSON-RPC code -32601); rethrow others.
+      if (err?.cause?.code === -32601 || err?.message?.includes('Method not found')) {
+        return this.aztecNode.getCurrentMinFees();
+      }
+      throw err;
     }
   }