DEVX-163: fix: check stdout for HTTP 500 in _run_push (docker sends to stdout)

src/devx/tools/build_image.py

@@ -266,6 +266,9 @@ def _run_push(cmd: list[str]) -> subprocess.CompletedProcess[str]:
     BlobUploader.Append that causes intermittent HTTP 500 "offset
     mismatch" errors during concurrent blob uploads.  Retrying the
     push gives the registry time to recover.
+
+    Docker sends push progress/errors to both stdout and stderr depending
+    on the error type, so both streams are checked for the 500 status.
     """
     result = subprocess.run(  # nosec B603
         cmd,
@@ -273,8 +276,10 @@ def _run_push(cmd: list[str]) -> subprocess.CompletedProcess[str]:
         text=True,
         check=False,
     )
-    if result.returncode != 0 and "500" in result.stderr:
-        raise PushHTTP500Error(result.stderr.strip())
+    if result.returncode != 0:
+        combined = f"{result.stderr}\n{result.stdout}"
+        if "500" in combined:
+            raise PushHTTP500Error(combined.strip())
     return result
 
 
@@ -329,10 +334,10 @@ def push_image(
         if result.returncode == 0:
             click.echo(f"Pushed {ft}")
             continue
-        stderr = result.stderr.strip()
+        combined_output = f"{result.stderr}\n{result.stdout}".strip()
         # Gitea #31964: push fails because tag already exists.
         # Delete the old manifest and retry once.
-        if username and token and "already exists" in stderr.lower():
+        if username and token and "already exists" in combined_output.lower():
             click.echo("  Tag exists (Gitea #31964), deleting old manifest and retrying...")
             delete_remote_manifest(
                 registry,
@@ -352,9 +357,9 @@ def push_image(
             if result.returncode == 0:
                 click.echo(f"Pushed {ft} (after retry)")
                 continue
-            stderr = result.stderr.strip()
+            combined_output = f"{result.stderr}\n{result.stdout}".strip()
         click.echo(
-            _("Push failed for {tag}: {error}", tag=ft, error=stderr),
+            _("Push failed for {tag}: {error}", tag=ft, error=combined_output),
             err=True,
         )
         all_ok = False