docs(audience-http): plain-language comment pass

Rewrites jargon (2xx server acked, serialise, diagnostic must not
block the success path) into plain language.

No code changes. All 184 tests pass.

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

Author: ImmutableJeffrey

src/Packages/Audience/Runtime/ImmutableAudience.cs

@@ -555,10 +555,10 @@ public static async Task FlushAsync(CancellationToken cancellationToken = defaul
 
             queue.FlushSync();
 
-            // Serialise SendBatchAsync via _sendInFlight. Without the gate,
-            // two concurrent FlushAsync callers both call ReadBatch with the
-            // same paths and double-POST. Poll cheaply while another caller
-            // (timer SendBatch or a racing FlushAsync) holds the gate.
+            // Only one send runs at a time. Without this, two FlushAsync
+            // callers would both read the same batch from disk and send it
+            // twice. Yield while another caller (the timer or another
+            // FlushAsync) holds the in-flight slot.
             while (Interlocked.CompareExchange(ref _sendInFlight, 1, 0) != 0)
             {
                 cancellationToken.ThrowIfCancellationRequested();

src/Packages/Audience/Runtime/Transport/HttpTransport.cs

@@ -99,9 +99,10 @@ internal async Task<bool> SendBatchAsync(CancellationToken ct = default)
 
                 if (statusCode >= 200 && statusCode < 300)
                 {
-                    // 2xx: server acked. Parse {accepted, rejected} and surface
-                    // any partial rejections via onError — rejected events are
-                    // validation errors, won't succeed on retry.
+                    // Server accepted the batch. Count how many messages it
+                    // rejected; if any, tell the studio via onError. Rejected
+                    // messages are validation failures — retrying won't help,
+                    // so the batch is deleted either way.
                     var rejected = await ParseRejectedCount(response).ConfigureAwait(false);
                     _store.Delete(batch);
                     ResetBackoff();
@@ -233,9 +234,9 @@ private void ResetBackoff()
             return sb.ToString();
         }
 
-        // Reads the body and extracts "rejected". Returns 0 on any parse or
-        // read failure — the body is diagnostic, so a malformed one must not
-        // block the success path.
+        // Reads the response body and pulls out the "rejected" count. Returns
+        // 0 if the body is missing or unreadable — the body is only for
+        // reporting, so failing to read it must not break the success path.
         private static async Task<int> ParseRejectedCount(HttpResponseMessage response)
         {
             string body;