Address second-round PR review feedback

Make _inject_bdn_extensions idempotent
- Re-running the scenario locally (or retry on the same checkout) used
  to append a fresh ItemGroup with Label="PerfLabInjected" and a fresh
  ProjectReference to BDN.Extensions every time, leaving stale entries
  that produce duplicate-reference build errors.
- Now the helper removes any prior PerfLabInjected ItemGroups before
  inserting the new one, so the patched csproj converges on a single
  injected ItemGroup regardless of how many times the scenario runs.

Forward unknown args to BenchmarkDotNet
- --bdn-args was declared with nargs='*', which argparse will not
  populate with values that start with '--'. The flag was effectively
  unusable for forwarding BDN options.
- Drop --bdn-args entirely and switch parse_args() to
  parser.parse_known_args(), so any unrecognized arguments (filters,
  iteration counts, etc.) flow straight through to BenchmarkDotNet.
- Documented in the parser epilog.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: LoopedBard3

src/scenarios/mauiDesktopBenchmarks/test.py

@@ -251,21 +251,25 @@ def build_maui_dependencies(repo_dir: str = MAUI_REPO_DIR):
 
 
 def parse_args():
-    parser = ArgumentParser(description='Run MAUI desktop BDN benchmarks')
+    parser = ArgumentParser(
+        description='Run MAUI desktop BDN benchmarks',
+        epilog='Any unrecognized arguments are forwarded to BenchmarkDotNet '
+               '(e.g. --filter MyBenchmark*).')
     parser.add_argument('--framework', '-f', default='net11.0',
                         help='Target .NET framework (determines MAUI repo branch)')
     parser.add_argument('--suite', choices=['core', 'xaml', 'graphics', 'all'],
                         default='all', help='Which benchmark suite to run')
-    parser.add_argument('--bdn-args', nargs='*', default=[],
-                        help='Additional arguments to pass to BenchmarkDotNet')
     parser.add_argument('--upload-to-perflab-container', action='store_true',
                         help='Upload results to perflab container')
-    return parser.parse_args()
+    # Forward unknown args to BenchmarkDotNet.  argparse's nargs='*' would
+    # not capture values that start with '--' (BDN flags), so use
+    # parse_known_args() instead and pass the remainder through.
+    return parser.parse_known_args()
 
 
 if __name__ == '__main__':
     setup_loggers(True)
-    args = parse_args()
+    args, extra_bdn_args = parse_args()
 
     # MAUI-specific: clone repo and build dependencies
     branch = get_branch(args.framework)
@@ -284,8 +288,9 @@ def parse_args():
     # MAUI-specific: build BuildTasks solution filter
     build_maui_dependencies()
 
-    # Run the generic BDN workflow
-    bdn_args = list(args.bdn_args)
+    # Run the generic BDN workflow.  Forward any args we didn't consume
+    # (e.g. --filter, --maxIterationCount overrides) to BenchmarkDotNet.
+    bdn_args = list(extra_bdn_args)
     if EXCLUDED_BENCHMARKS:
         bdn_args.extend(['--exclusion-filter'] + EXCLUDED_BENCHMARKS)
     helper.runtests(args.suite, bdn_args, args.upload_to_perflab_container)

src/scenarios/shared/bdndesktop.py

@@ -164,7 +164,13 @@ def _find_bdn_extensions(self) -> str:
         return candidate
 
     def _inject_bdn_extensions(self, csproj_path: str, bdn_ext_abs: str):
-        '''Add a ProjectReference to BDN.Extensions and remove existing BDN PackageRef.'''
+        '''Add a ProjectReference to BDN.Extensions and remove existing BDN PackageRef.
+
+        Idempotent: removes any prior ItemGroup with Label="PerfLabInjected"
+        before adding the new one so re-running against an existing
+        checkout does not accumulate duplicate ProjectReference entries
+        (which produce build errors).
+        '''
         log = getLogger()
         log.info(f'Injecting BDN.Extensions reference into {os.path.basename(csproj_path)}')
 
@@ -178,6 +184,15 @@ def _inject_bdn_extensions(self, csproj_path: str, bdn_ext_abs: str):
         if root.tag.startswith('{'):
             ns = root.tag.split('}')[0] + '}'
 
+        # Remove any prior PerfLabInjected ItemGroup so re-runs don't
+        # accumulate duplicate ProjectReferences.
+        existing_injected = [ig for ig in root.findall(f'{ns}ItemGroup')
+                             if ig.get('Label') == 'PerfLabInjected']
+        for ig in existing_injected:
+            root.remove(ig)
+        if existing_injected:
+            log.info(f'  Removed {len(existing_injected)} prior PerfLabInjected ItemGroup(s)')
+
         # Remove BDN package references that conflict with the injected
         # ProjectReference to BenchmarkDotNet.Extensions (which itself
         # references BenchmarkDotNet + BenchmarkDotNet.Annotations as