fix: reddit feed user-agent set as raw header so the refresh job no longer fails

Author: chutch3

api/API/Discovery/RedditFeedClient.cs

@@ -5,6 +5,15 @@ namespace API.Discovery;
 /// <summary>Reddit's public Atom feeds. Reddit rate-limits aggressively (429), so callers cache and degrade.</summary>
 public class RedditFeedClient(HttpClient http) : IRedditFeedClient
 {
+    /// <summary>Reddit's recommended User-Agent shape (platform:appid (comment)).</summary>
+    public const string UserAgent = "kenku:discovery (self-hosted manga manager)";
+
+    /// <summary>Sets the reddit User-Agent as a raw header — the typed <c>UserAgent.ParseAdd</c> rejects
+    /// this otherwise-valid value and throws at client construction.</summary>
+    public static void ConfigureClient(HttpClient client) =>
+        client.DefaultRequestHeaders.TryAddWithoutValidation("User-Agent", UserAgent);
+
+
     public async Task<List<DiscoveryEntry>> GetHotAsync(string subreddit, int limit, CancellationToken ct)
     {
         using HttpResponseMessage response = await http.GetAsync(

api/API/Extensions/ApplicationServiceCollectionExtensions.cs

@@ -141,8 +141,8 @@ public static IServiceCollection AddKenkuServices(this IServiceCollection servic
         // Discovery rails: edge clients own their HTTP; results cache for an hour per rail.
         services.AddSingleton<API.Discovery.DiscoveryCache>();
         services.AddHttpClient<API.Discovery.IAniListClient, API.Discovery.AniListClient>();
-        services.AddHttpClient<API.Discovery.IRedditFeedClient, API.Discovery.RedditFeedClient>(c =>
-            c.DefaultRequestHeaders.UserAgent.ParseAdd("kenku:discovery (self-hosted manga manager)"));
+        services.AddHttpClient<API.Discovery.IRedditFeedClient, API.Discovery.RedditFeedClient>(
+            API.Discovery.RedditFeedClient.ConfigureClient);
         services.AddSingleton<Kenku>();
         return services;
     }

api/Tests/Unit/Discovery/RedditFeedClientTests.cs

@@ -6,6 +6,20 @@ namespace API.Tests.Unit.Discovery;
 /// <summary>Atom shape pinned against a captured live r/manga feed (2026-06-11).</summary>
 public class RedditFeedClientTests
 {
+    [Fact]
+    public void ConfigureClient_SetsTheUserAgent_WithoutTrippingTheStrictHeaderParser()
+    {
+        // Reddit's recommended UA ("kenku:discovery (self-hosted manga manager)") is rejected by the
+        // typed UserAgent parser, which previously threw at client construction and wedged the feed
+        // job in NeedsAttention. It must be set as a raw header instead.
+        using var client = new HttpClient();
+
+        RedditFeedClient.ConfigureClient(client);
+
+        Assert.True(client.DefaultRequestHeaders.TryGetValues("User-Agent", out var values));
+        Assert.Equal(RedditFeedClient.UserAgent, Assert.Single(values!));
+    }
+
     private const string Feed = """
         <?xml version="1.0" encoding="UTF-8"?>
         <feed xmlns="http://www.w3.org/2005/Atom" xmlns:media="http://search.yahoo.com/mrss/">