fix(images): swallow RuntimeBinderException in cover-lookup fallback

CHANGELOG.md

@@ -5,6 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+- **Cover-image lookup no longer 500s when one upstream metadata source returns a partial envelope:** `ImagesController.GetImage`'s fallback metadata-driven cover path accesses `env.metadata` on `GetMetadataAsync`'s `object?` return via the C# `dynamic` binder. When the returned envelope shape lacks a `metadata` property — which happens when one of the upstream sources (e.g., Audnexus) 500s and the service still returns a partial envelope — the binder throws `RuntimeBinderException`. That exception wasn't in `IsRecoverableImageLookupException`'s whitelist, so it bypassed the inner catch and the entire image endpoint returned 500. Adding `RuntimeBinderException` to the recoverable list lets the inner catch swallow the bad envelope and the lookup falls through to the next candidate URL or a placeholder, matching how the other recoverable failures behave.
+
 ## [0.2.71] - 2026-04-17
 
 ### Added

listenarr.api/Controllers/ImagesController.cs

@@ -1040,7 +1040,16 @@ or ArgumentException
                 or FormatException
                 or UriFormatException
                 or System.Net.Http.HttpRequestException
-                or System.Text.Json.JsonException;
+                or System.Text.Json.JsonException
+                // GetMetadataAsync returns object?, and the fallback metadata path
+                // accesses fields via dynamic. When the returned envelope shape
+                // lacks the expected `metadata` property (e.g., when one of the
+                // upstream sources like Audnexus 500s and the service still
+                // returns a partial envelope), the C# dynamic binder throws
+                // RuntimeBinderException. Without this in the recoverable filter,
+                // a single bad envelope shape bubbles up to the outer catch and
+                // turns the whole image lookup into a 500.
+                or Microsoft.CSharp.RuntimeBinder.RuntimeBinderException;
         }
 
         private static string ResolvePathWithOptionalBase(string? basePath, string candidatePath)