From 38439550bbc71facf117f046fe967d597595db81 Mon Sep 17 00:00:00 2001
From: Sasha Mitchell <sash.t.mitchell@gmail.com>
Date: Fri, 25 Sep 2026 22:47:02 +0700
Subject: [PATCH] fix: keep lovelace amounts that do not fit in a JS number

MeshValue.toJSON passed the quantity through Number, so 9007199254740993 lovelace became 9007199254740992.
---
 packages/mesh-common/src/data/value.ts          | 17 ++++++++++++-----
 .../test/data/value/convertor.test.ts           |  9 +++++++++
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/packages/mesh-common/src/data/value.ts b/packages/mesh-common/src/data/value.ts
index 5d3d4d689..1a26c9fce 100644
--- a/packages/mesh-common/src/data/value.ts
+++ b/packages/mesh-common/src/data/value.ts
@@ -23,6 +23,12 @@ import {
 const compareByteOrder = (a: string, b: string): number =>
   a < b ? -1 : a > b ? 1 : 0;
 
+// A JS number cannot hold every lovelace amount. 2^53 + 1 is still under max ADA.
+const jsInteger = (amount: bigint): number | bigint => {
+  const asNumber = Number(amount);
+  return BigInt(asNumber) === amount ? asNumber : amount;
+};
+
 /**
  * Aiken alias
  * Value is the JSON representation of Cardano data Value
@@ -377,7 +383,7 @@ export class MeshValue {
   toJSON = (): Value => {
     const valueMapToParse: [CurrencySymbol, AssocMap<TokenName, Integer>][] =
       [];
-    const valueMap: { [key: string]: { [key: string]: number } } = {};
+    const valueMap: { [key: string]: { [key: string]: bigint } } = {};
 
     this.toAssets().forEach((asset) => {
       const sanitizedName = asset.unit.replace("lovelace", "");
@@ -388,10 +394,11 @@ export class MeshValue {
         valueMap[policy] = {};
       }
 
-      if (!valueMap[policy]![token]) {
-        valueMap[policy]![token] = Number(asset.quantity);
+      const quantity = BigInt(asset.quantity);
+      if (valueMap[policy]![token] === undefined) {
+        valueMap[policy]![token] = quantity;
       } else {
-        valueMap[policy]![token] += Number(asset.quantity);
+        valueMap[policy]![token] += quantity;
       }
     });
 
@@ -406,7 +413,7 @@ export class MeshValue {
       );
       const tokens: [TokenName, Integer][] = sortedTokenNames.map((name) => [
         tokenName(name),
-        integer(valueMap[policy]![name]!),
+        integer(jsInteger(valueMap[policy]![name]!)),
       ]);
 
       const policyMap = assocMap(tokens);
diff --git a/packages/mesh-common/test/data/value/convertor.test.ts b/packages/mesh-common/test/data/value/convertor.test.ts
index 673e8700f..7de6299e6 100644
--- a/packages/mesh-common/test/data/value/convertor.test.ts
+++ b/packages/mesh-common/test/data/value/convertor.test.ts
@@ -305,6 +305,15 @@ describe("MeshValue class", () => {
       expect(JSON.stringify(jsonValue)).toEqual(JSON.stringify(expectedValue));
     });
 
+    test("keeps a lovelace quantity that does not fit in a JS number", () => {
+      const quantity = "9007199254740993";
+      const meshValue = new MeshValue();
+      meshValue.toAssets = () => [{ unit: "lovelace", quantity }];
+
+      const jsonValue = meshValue.toJSON();
+      expect(jsonValue.map[0].v.map[0].v.int).toBe(BigInt(quantity));
+    });
+
     test("should correctly convert MeshValue to JSON with no asset", () => {
       const assets: Asset[] = [];