fix(waproto): normalize high to int32 + tighten roundtrip test

Addresses 2 review comments on PR #385:

1. CodeRabbit Major — longToString/longToNumber checked
   `value.high < 0` on the raw input. When a Long-like object carries
   high as an unsigned 32-bit value (e.g. raw {low, high} from JSON
   deserialization, not constructed via Long.fromBits/fromValue which
   normalize via `| 0`), the sign-bit detection fails and the value is
   interpreted as unsigned. Example: {low: 0, high: 0xFFFFFFFF} signed
   should be -4294967296 but returned 18446744069414584320.

   Fix: `const high = value.high | 0` before the sign check. Applied
   to both helpers in WAProto/index.js (generated artifact) and
   WAProto/fix-imports.js (template). Diverges from upstream Baileys
   PR #2333 which has the same latent bug.

   Added 2 test cases in bigint-validation.test.ts for the raw
   {low, high} scenario (Long.fromBits would mask the bug because it
   normalizes internally).

2. CodeRabbit Nitpick — the encode/decode roundtrip test in
   proto-tojson-long.test.ts used safe integers (1700000000 and
   123456789), which would silently pass even if longToString fell
   back to Number(value). Switched to uint64 values above
   MAX_SAFE_INTEGER (max uint64 and 9999999999999999999) so the
   roundtrip actually exercises the BigInt fast path.

Test suite: 789/789 passing (+2 cases for the unsigned-high scenario).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/__tests__/bigint-validation.test.ts

@@ -19,10 +19,11 @@ function longToStringNew(value: any, unsigned?: boolean): string {
 	if (typeof value === 'string') return value
 	if (typeof value === 'number') return String(value)
 	if (value && typeof value.low === 'number' && typeof value.high === 'number') {
+		const high = value.high | 0
 		const lo = BigInt(value.low >>> 0)
 		const hi = BigInt(value.high >>> 0)
 		const combined = (hi << 32n) | lo
-		if (!unsigned && value.high < 0) {
+		if (!unsigned && high < 0) {
 			return (combined - (1n << 64n)).toString()
 		}
 
@@ -50,10 +51,11 @@ function longToNumberNew(value: any, unsigned?: boolean): number {
 	if (typeof value === 'number') return value
 	if (typeof value === 'string') return Number(value)
 	if (value && typeof value.low === 'number' && typeof value.high === 'number') {
+		const high = value.high | 0
 		const lo = BigInt(value.low >>> 0)
 		const hi = BigInt(value.high >>> 0)
 		const combined = (hi << 32n) | lo
-		if (!unsigned && value.high < 0) {
+		if (!unsigned && high < 0) {
 			return Number(combined - (1n << 64n))
 		}
 
@@ -158,6 +160,27 @@ describe('BigInt vs Long equivalence validation', () => {
 		it('object without low/high', () => {
 			expect(longToStringNew({ foo: 'bar' })).toBe('[object Object]')
 		})
+
+		// Defensive: a raw {low, high} JSON object can carry `high` as an
+		// unsigned 32-bit value (Long.fromBits would normalize via `| 0`,
+		// but plain JSON deserialization does not). Without `value.high | 0`
+		// the sign-bit check fails and the result is interpreted as unsigned.
+		// Upstream Baileys PR #2333 has this latent bug; InfiniteAPI fixes it.
+		it('signed sign-bit detection on raw unsigned high (-1 as {low: -1, high: 4294967295})', () => {
+			const raw = { low: -1, high: 0xffffffff }
+			// signed: -1
+			expect(longToStringNew(raw, false)).toBe('-1')
+			// unsigned: max uint64
+			expect(longToStringNew(raw, true)).toBe('18446744073709551615')
+		})
+
+		it('signed sign-bit detection on raw unsigned high (-4294967296 as {low: 0, high: 4294967295})', () => {
+			const raw = { low: 0, high: 0xffffffff }
+			// signed: -4294967296 (high word = -1 after normalization)
+			expect(longToStringNew(raw, false)).toBe('-4294967296')
+			// unsigned: 0xFFFFFFFF00000000 = 18446744069414584320
+			expect(longToStringNew(raw, true)).toBe('18446744069414584320')
+		})
 	})
 
 	describe('fuzz: random Long values', () => {

src/__tests__/proto-tojson-long.test.ts

@@ -90,17 +90,21 @@ describe('proto serialization', () => {
 		expect(json.message?.imageMessage?.fileLength).toBe('1')
 	})
 
-	it('roundtrips encode/decode with Long fields preserving values', () => {
+	it('roundtrips encode/decode with Long fields preserving values (> MAX_SAFE_INTEGER)', () => {
+		// Use uint64 values above Number.MAX_SAFE_INTEGER (2^53 - 1) so the
+		// roundtrip actually exercises the BigInt fast path on decode->toJSON.
+		// Safe integers would silently work even if longToString fell back to
+		// Number(value).
 		const original = proto.WebMessageInfo.fromObject({
 			key: {
 				remoteJid: '123@s.whatsapp.net',
 				id: 'ABC123',
 				fromMe: false
 			},
-			messageTimestamp: 1700000000,
+			messageTimestamp: Long.fromString('18446744073709551615', true),
 			message: {
 				imageMessage: {
-					fileLength: 123456789
+					fileLength: Long.fromString('9999999999999999999', true)
 				}
 			}
 		})
@@ -109,7 +113,7 @@ describe('proto serialization', () => {
 		const decoded = proto.WebMessageInfo.decode(encoded)
 		const json = decoded.toJSON()
 
-		expect(json.messageTimestamp).toBe('1700000000')
-		expect(json.message?.imageMessage?.fileLength).toBe('123456789')
+		expect(json.messageTimestamp).toBe('18446744073709551615')
+		expect(json.message?.imageMessage?.fileLength).toBe('9999999999999999999')
 	})
 })