Restore IsStreamingMode on recovery; guard superseded-load else-branch

RecoverFromFailedRefill now sets IsStreamingMode=true so the in-place
seek-retry route isn't wedged. The generic-catch unload path is gated on
the loadCts identity, so a superseded load no longer clobbers a newer
operation's state.

DeepDrftTests/SegmentedStreamLoopTests.cs

@@ -353,6 +353,8 @@ public class SegmentedStreamLoopTests
                 "a truncated segment while cursor < totalLength is a failure: scheduler must be halted via recovery");
             Assert.That(player.IsLoaded, Is.True,
                 "recovery leaves the track loaded so the listener can retry — not torn down to unloaded");
+            Assert.That(player.IsStreamingMode, Is.True,
+                "recovery must restore IsStreamingMode=true so Seek() is not wedged (AC6 / Phase 21.3 retry contract)");
             Assert.That(player.IsPaused, Is.True,
                 "recovery settles into a paused state, not playing");
             Assert.That(player.ErrorMessage, Is.Not.Null.And.Not.Empty,
@@ -381,6 +383,8 @@ public class SegmentedStreamLoopTests
                 "a mid-stream fetch failure must halt the scheduler via recovery, not leave it to drain");
             Assert.That(player.IsLoaded, Is.True,
                 "recovery leaves the track loaded so the listener can retry — not torn down to unloaded");
+            Assert.That(player.IsStreamingMode, Is.True,
+                "recovery must restore IsStreamingMode=true so Seek() is not wedged (AC6 / Phase 21.3 retry contract)");
             Assert.That(player.IsPaused, Is.True,
                 "recovery settles into a paused state, not playing");
             Assert.That(player.ErrorMessage, Is.Not.Null.And.Not.Empty,