fix: name the HTTP status when the error body is not JSON (#58)

An unparseable error body produced the message "failed to parse error
response", which hid the HTTP status. The message now appends the status
to that text, so prefix matching and substring matching both keep
working. The status code, the raw response body and the parse cause do
not change.

Author: mogita

src/Http/GuzzleHttpClient.php

@@ -467,7 +467,7 @@ private function buildApiException(
 
         if (!$parsedEnvelope) {
             // HTTP layer succeeded, body is unparseable as APIError.
-            $message = 'failed to parse error response';
+            $message = sprintf('failed to parse error response: unexpected server response code %d', $statusCode);
         }
 
         if ($statusCode === 429) {

tests/Exceptions/ErrorHandlingTest.php

@@ -106,7 +106,7 @@ public function unparseableErrorResponseFallsBackToSentinelMessage(): void
             self::assertSame(500, $e->getStatusCode());
             self::assertSame(500, $e->getCode(), 'getCode() returns HTTP status (back-compat)');
             self::assertSame(0, $e->getApiErrorCode(), 'APIError.code is 0 on unparseable body');
-            self::assertSame('failed to parse error response', $e->getMessage());
+            self::assertSame('failed to parse error response: unexpected server response code 500', $e->getMessage());
             self::assertSame('<<<not json>>>', $e->getRawResponseBody());
             self::assertNotNull($e->getPrevious(), 'cause chain must point to the JSON parse error');
             self::assertInstanceOf(\JsonException::class, $e->getPrevious());