Treat only 2xx as a successful upload

Every one of these SDKs treated a 3xx as a failure before this work, and the
change to 200-399 came from the design doc's "Spec item 1: 2xx and 3xx are
success". That line is wrong, and the doc is what needs correcting.

Measured against a local server, with the same HTTP clients these SDKs use:

  307/308 + Location  -> followed as POST with the body, arrives as 200
  301/302/303 + Loc.  -> followed as GET with no body, arrives as 200
  302 without Location-> surfaces raw as 302
  300 Multiple Choices-> surfaces raw as 300
  304 Not Modified    -> surfaces raw as 304

So a raw 3xx only reaches the classifier when the client has already declined to
follow it, meaning nothing was uploaded. The one redirect that genuinely works,
307/308, never produces a 3xx here at all — it produces 200 — so narrowing the
bound cannot break it. Nothing was gained by the wider range; a 300, 304, or
Location-less 302 from a proxy was being logged as a delivered batch and dropped
with no error callback.

The narrower bound also needs no new branches: a 3xx is neither 5xx nor in the
retryable 4xx set, so it already falls through to the non-retryable path and
reports a failure.

TAPI does not emit 3xx and has no plans to. This matters because host is
customer-configurable and proxies in front of it are common.

curl is not configured to follow redirects, so php can also see a raw 3xx; it now reports a named redirect error instead of an empty body. Socket narrowed to match.

Author: MichaelGHSeg

lib/Consumer/LibCurl.php

@@ -62,11 +62,23 @@ public function flushBatch(array $messages): bool
                 return false;
             }
 
-            // 2xx and 3xx are success
-            if ($responseCode >= 200 && $responseCode < 400) {
+            // Only 2xx is success. curl is not configured to follow redirects, so a
+            // 3xx means nothing was uploaded; treating it as success would drop the
+            // batch silently. TAPI does not emit 3xx — this shows up when the
+            // configured host is a proxy or redirector.
+            if ($responseCode >= 200 && $responseCode < 300) {
                 return true;
             }
 
+            if ($responseCode >= 300 && $responseCode < 400) {
+                $this->handleError(
+                    $responseCode,
+                    'Unexpected redirect; batch not uploaded. Check whether the configured '
+                    . 'host points at a proxy or redirector.'
+                );
+                return false;
+            }
+
             $this->handleError($responseCode, $responseContent);
 
             if (!$this->isRetryable($responseCode)) {

lib/Consumer/Socket.php

@@ -187,8 +187,9 @@ private function makeRequest($socket, string $req, string $payload): bool
             }
             fclose($socket);
 
-            // 2xx and 3xx are success
-            if ($statusCode >= 200 && $statusCode < 400) {
+            // Only 2xx is success; a raw socket never follows redirects, so a 3xx
+            // means nothing was uploaded.
+            if ($statusCode >= 200 && $statusCode < 300) {
                 return true;
             }