diff --git a/DeepDrftAPI/Controllers/TrackController.cs b/DeepDrftAPI/Controllers/TrackController.cs
index 015c11f..a277cbb 100644
--- a/DeepDrftAPI/Controllers/TrackController.cs
+++ b/DeepDrftAPI/Controllers/TrackController.cs
@@ -47,24 +47,25 @@ public class TrackController : ControllerBase
         _logger = logger;
     }
 
-    // Streams an uploaded audio body to a freshly-named staging file on the data disk, preserving the
-    // validated extension (the processor router selects by extension and reads from disk; .tmp would be
-    // rejected). Staging lives under UploadStagingDirectory, never Path.GetTempPath() — on the Linux
-    // host /tmp is a small tmpfs that cannot hold a large WAV. Returns the staging path; the caller
-    // owns deletion in a finally block.
-    private async Task<string> StageUploadAsync(
-        IFormFile audioFile, string uploadExtension, CancellationToken cancellationToken)
-    {
-        var stagingPath = Path.Combine(
-            _stagingDirectory.Path, Guid.NewGuid().ToString("N") + uploadExtension);
+    // Builds a unique staging file path on the data disk with the validated extension. The caller MUST
+    // assign this to the local that its finally block guards BEFORE calling StageUploadAsync — that
+    // way a mid-copy abort (OperationCanceledException, IO error) still triggers deletion of the
+    // partially-written file. Staging lives under UploadStagingDirectory, never Path.GetTempPath() —
+    // on the Linux host /tmp is a small tmpfs that cannot hold a large WAV.
+    private string BuildStagingPath(string uploadExtension) =>
+        Path.Combine(_stagingDirectory.Path, Guid.NewGuid().ToString("N") + uploadExtension);
 
+    // Streams an uploaded audio body to the pre-allocated staging path. The caller owns the path and
+    // must delete it in a finally block; separating path generation from the copy ensures the finally
+    // guard fires even when CopyToAsync throws before returning.
+    private async Task StageUploadAsync(
+        IFormFile audioFile, string stagingPath, CancellationToken cancellationToken)
+    {
         await using var stagingStream = new FileStream(
             stagingPath, FileMode.CreateNew, FileAccess.Write, FileShare.None,
             bufferSize: 81920, useAsync: true);
         await using var uploadStream = audioFile.OpenReadStream();
         await uploadStream.CopyToAsync(stagingStream, cancellationToken);
-
-        return stagingPath;
     }
 
     // Best-effort removal of a staging file. Logs and swallows — a stranded staging file is a
@@ -359,10 +360,12 @@ public class TrackController : ControllerBase
 
         var resolvedTrackNumber = trackNumber is > 0 ? trackNumber.Value : 1;
 
-        string? stagingPath = null;
+        // Build the staging path before the copy so the finally block can delete the partial file
+        // even if CopyToAsync throws mid-stream (client cancellation, disk-full, IO error).
+        var stagingPath = BuildStagingPath(uploadExtension);
         try
         {
-            stagingPath = await StageUploadAsync(audioFile, uploadExtension, cancellationToken);
+            await StageUploadAsync(audioFile, stagingPath, cancellationToken);
 
             var result = await _unifiedService.UploadAsync(
                 stagingPath,
@@ -411,10 +414,7 @@ public class TrackController : ControllerBase
         }
         finally
         {
-            if (stagingPath is not null)
-            {
-                DeleteStagingFile(stagingPath);
-            }
+            DeleteStagingFile(stagingPath);
         }
     }
 
@@ -590,10 +590,12 @@ public class TrackController : ControllerBase
             return BadRequest("Uploaded file must have a .wav, .mp3, or .flac extension");
         }
 
-        string? stagingPath = null;
+        // Build the staging path before the copy so the finally block can delete the partial file
+        // even if CopyToAsync throws mid-stream (client cancellation, disk-full, IO error).
+        var stagingPath = BuildStagingPath(uploadExtension);
         try
         {
-            stagingPath = await StageUploadAsync(audioFile, uploadExtension, cancellationToken);
+            await StageUploadAsync(audioFile, stagingPath, cancellationToken);
 
             var result = await _unifiedService.ReplaceAudioAsync(id, stagingPath, cancellationToken);
             if (result.Success)
@@ -618,10 +620,7 @@ public class TrackController : ControllerBase
         }
         finally
         {
-            if (stagingPath is not null)
-            {
-                DeleteStagingFile(stagingPath);
-            }
+            DeleteStagingFile(stagingPath);
         }
     }
 
diff --git a/DeepDrftTests/UploadStagingPathTests.cs b/DeepDrftTests/UploadStagingPathTests.cs
index b55135b..02c593c 100644
--- a/DeepDrftTests/UploadStagingPathTests.cs
+++ b/DeepDrftTests/UploadStagingPathTests.cs
@@ -51,6 +51,12 @@ public class UploadStagingPathTests
         var resolved = Startup.ResolveStagingPath(configuredPath: null, vaultPath);
 
         var systemTemp = Path.GetFullPath(Path.GetTempPath());
+        // Note: because vaultPath is relative, Path.GetFullPath resolves it against the CWD, which is
+        // never the system temp directory. The StartsWith guard therefore catches the case where
+        // ResolveStagingPath mistakenly uses Path.GetTempPath() directly, rather than proving the
+        // absolute production path never overlaps with /tmp on any machine. The EndsWith assertion
+        // is the load-bearing check: it verifies the output is rooted under the vault tree, not
+        // under a hard-coded temp location.
         Assert.That(resolved.StartsWith(systemTemp, StringComparison.Ordinal), Is.False,
             "The default staging directory must never live under the system temp mount");
         Assert.That(resolved, Does.EndWith(Path.Combine("Database", "Vaults", "staging")),