update changelog with persistent backend error handling

changelog/unreleased/issue-4515

@@ -1,8 +0,0 @@
-Change: Don't retry to load files that don't exist
-
-Restic used to always retry to load files. It now only retries to load
-files if they exist.
-
-https://github.com/restic/restic/issues/4515
-https://github.com/restic/restic/issues/1523
-https://github.com/restic/restic/pull/4520

changelog/unreleased/issue-4627

@@ -1,4 +1,4 @@
-Enhancement: Improve reliability of backend operations
+Change: Redesign backend error handling to improve reliability
 
 Restic now downloads pack files in large chunks instead of using a streaming
 download. This prevents failures due to interrupted streams. The `restore`
@@ -6,12 +6,20 @@ command now also retries downloading individual blobs that cannot be retrieved.
 
 HTTP requests that are stuck for more than two minutes while uploading or
 downloading are now forcibly interrupted. This ensures that stuck requests are
-retried after a short timeout. These new request timeouts can temporarily be
-disabled by setting the environment variable
-`RESTIC_FEATURES=http-timeouts=false`. Note that this feature flag will be
-removed in the next minor restic version.
+retried after a short timeout.
+
+Attempts to access a missing file or a truncated file will no longer be retried.
+This avoids unnecessary retries in those cases.
+
+Most parts of the new backend error handling can temporarily be disabled by
+setting the environment variable
+`RESTIC_FEATURES=backend-error-redesign=false`. Note that this feature flag will
+be removed in the next minor restic version.
 
 https://github.com/restic/restic/issues/4627
 https://github.com/restic/restic/issues/4193
 https://github.com/restic/restic/pull/4605
 https://github.com/restic/restic/pull/4792
+https://github.com/restic/restic/issues/4515
+https://github.com/restic/restic/issues/1523
+https://github.com/restic/restic/pull/4520