fix: replace magic numbers with RetryReason enum constants

Address remaining Copilot review comments on PR #306:

- Import RetryReason enum from Utils (already re-exported via Utils/index.ts)
- Replace all numeric literals (0/1/2/3/4/7) in retryErrorCode with the
  corresponding enum members (UnknownError / SignalErrorNoSession / etc.)
- Removes inline comments that were only needed to explain magic numbers
- If RetryReason values ever change, the compiler will surface the drift

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Socket/messages-recv.ts

@@ -49,9 +49,12 @@ import {
 	getStatusFromReceiptType,
 	handleIdentityChange,
 	hkdf,
+	BAD_MAC_ERROR_TEXT,
+	DECRYPTION_RETRY_CONFIG,
 	MISSING_KEYS_ERROR_TEXT,
 	NACK_REASONS,
 	NO_MESSAGE_FOUND_ERROR_TEXT,
+	RetryReason,
 	normalizeKeyLidToPn,
 	normalizeMessageJids,
 	resolveLidToPn,
@@ -1312,25 +1315,37 @@ export const makeMessagesRecvSocket = (config: SocketConfig) => {
 		const fromJid = node.attrs.from!
 
 		// Derive the Signal error code from the actual decryption failure message.
-		// This is sent in the retry receipt so the peer (even another InfiniteAPI instance)
-		// knows the exact reason and can recreate the session immediately instead of waiting
-		// for the 1-hour timeout fallback.
+		// Sent in the retry receipt so the peer (even another InfiniteAPI instance)
+		// knows the exact failure type and can recreate the session immediately
+		// instead of falling back to the 1-hour timeout.
 		//
 		// Codes mirror RetryReason enum in message-retry-manager.ts:
 		//   0 = UnknownError | 1 = NoSession  | 2 = InvalidKey
-		//   3 = InvalidKeyId | 7 = BadMac (= SignalErrorInvalidMessage/InvalidCipherKey)
+		//   3 = InvalidKeyId | 4 = InvalidMessage | 7 = BadMac
+		//
+		// Uses DECRYPTION_RETRY_CONFIG error lists (single source of truth in
+		// decode-wa-message.ts) so additions to those lists are picked up here
+		// automatically.
 		//
 		// NOTE: We do NOT delete the session here (receiver side). The Signal Protocol
 		// recovers automatically when the sender's pkmsg arrives — it overwrites the
 		// corrupted session. Deleting prematurely creates a race window where no session
 		// exists, which can cause "No Session" errors on concurrent messages.
 		const retryErrorCode = (() => {
-			if (!decryptionError) return 0
-			if (/bad\s*mac/i.test(decryptionError)) return 7 // SignalErrorBadMac
-			if (/no\s*session/i.test(decryptionError)) return 1 // SignalErrorNoSession
-			if (/pre\s*key/i.test(decryptionError)) return 3 // SignalErrorInvalidKeyId
-			if (/invalid\s*key/i.test(decryptionError)) return 2 // SignalErrorInvalidKey
-			return 0
+			if (!decryptionError) return RetryReason.UnknownError
+			// Bad MAC must be checked first — it is also in corruptedSessionErrors
+			// but warrants the more specific code 7 over the generic code 4.
+			if (decryptionError.includes(BAD_MAC_ERROR_TEXT)) return RetryReason.SignalErrorBadMac
+			// MessageCounterError and other corrupted-session variants
+			if (DECRYPTION_RETRY_CONFIG.corruptedSessionErrors.some(e => decryptionError.includes(e))) return RetryReason.SignalErrorInvalidMessage
+			// Missing / invalid session record
+			if (DECRYPTION_RETRY_CONFIG.sessionRecordErrors.some(e => decryptionError.includes(e)) ||
+				/no\s+(open\s+)?sessions?/i.test(decryptionError)) return RetryReason.SignalErrorNoSession
+			// PreKey / key-id errors
+			if (/pre\s*key/i.test(decryptionError)) return RetryReason.SignalErrorInvalidKeyId
+			// Identity / key errors
+			if (/invalid\s*key|untrusted\s*identity/i.test(decryptionError)) return RetryReason.SignalErrorInvalidKey
+			return RetryReason.UnknownError
 		})()
 
 		if (retryCount <= 2) {