fix: improve error messages for swap operations

lib/contract.ts

@@ -131,7 +131,10 @@ import {
 
       if (txResponse.status !== "SUCCESS") {
         console.error(`Transaction failed for ${functName} with status: ${txResponse.status}`, JSON.stringify(txResponse, null, 2));
-        throw new Error(`Transaction failed with status: ${txResponse.status}`);
+        throw new Error(
+          `Transaction failed with status: ${txResponse.status} ` +
+          `(function: ${functName}, contract: ${targetContractId}, network: ${config.network})`
+        );
       }
 
       // Parse return value if present (e.g., for withdraw)
@@ -219,7 +222,10 @@ import {
     } catch (error: unknown) {
       const errorMessage = error instanceof Error ? error.message : String(error);
       console.error("Failed to swap:", errorMessage);
-      throw error;
+      throw new Error(
+        `Failed to swap (to=${to}, buyA=${buyA}, out=${out}, inMax=${inMax}, ` +
+        `network=${config?.network ?? "testnet"}): ${errorMessage}`
+      );
     }
   }
 

lib/dex.ts

@@ -195,7 +195,16 @@ export async function quoteSwap(
   const response = await fetchImpl(buildPathEndpointUrl(client, params));
 
   if (!response.ok) {
-    throw new Error(`Failed to fetch path quotes: ${response.status} ${response.statusText}`);
+    const sendAssetLabel = assetInputToHorizonAsset(params.sendAsset);
+    const destAssetLabel = assetInputToHorizonAsset(params.destAsset);
+    const amountLabel = params.mode === "strict-send"
+      ? `sendAmount=${params.sendAmount}`
+      : `destAmount=${params.destAmount}`;
+    throw new Error(
+      `Failed to fetch path quotes for ${params.mode} swap ` +
+      `(${sendAssetLabel} → ${destAssetLabel}, ${amountLabel}) ` +
+      `on ${client.network}: ${response.status} ${response.statusText}`
+    );
   }
 
   const payload = (await response.json()) as HorizonPathResponse;
@@ -223,7 +232,16 @@ export async function swapBestRoute(
   const bestQuote = quotes[0];
 
   if (!bestQuote) {
-    throw new Error("No route available for the requested swap");
+    const sendAssetLabel = assetInputToHorizonAsset(params.sendAsset);
+    const destAssetLabel = assetInputToHorizonAsset(params.destAsset);
+    const amountLabel = params.mode === "strict-send"
+      ? `sendAmount=${params.sendAmount}`
+      : `destAmount=${params.destAmount}`;
+    throw new Error(
+      `No route available for ${params.mode} swap ` +
+      `(${sendAssetLabel} → ${destAssetLabel}, ${amountLabel}) ` +
+      `on ${client.network}`
+    );
   }
 
   const createServer =
@@ -417,7 +435,8 @@ async function validateDestinationAssetSupport(
 
   if (!supportsAsset) {
     throw new Error(
-      "Destination account does not trust the requested destination asset"
+      `Destination account ${destination} does not trust asset ${destAsset.code}:${destAsset.issuer}. ` +
+      `The destination account must have a trustline for this asset before receiving it.`
     );
   }
 }

tests/integration/dex-workflow.test.ts

@@ -158,7 +158,7 @@ describe("dex workflow", () => {
         },
         { fetchImpl }
       )
-    ).rejects.toThrow("No route available");
+    ).rejects.toThrow("No route available for");
   });
 
   it("surfaces destination trustline-style submission failures", async () => {

tests/unit/lib/dex.test.ts

@@ -368,7 +368,7 @@ describe("dex helpers", () => {
         },
         { fetchImpl }
       )
-    ).rejects.toThrow("Destination account does not trust the requested destination asset");
+    ).rejects.toThrow("does not trust asset EUR:");
 
     expect(fetchImpl).toHaveBeenCalledTimes(1);
   });