DEVX-163: fix: use stderr=STDOUT to capture all docker push output in one stream

src/devx/tools/build_image.py

@@ -269,17 +269,19 @@ def _run_push(cmd: list[str]) -> subprocess.CompletedProcess[str]:
 
     Docker sends push progress/errors to both stdout and stderr depending
     on the error type, so both streams are checked for the 500 status.
+    Uses stderr=STDOUT to merge both streams into stdout, ensuring all
+    output is captured in one place (docker push output behavior varies
+    depending on TTY detection).
     """
     result = subprocess.run(  # nosec B603
         cmd,
-        capture_output=True,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
         text=True,
         check=False,
     )
-    if result.returncode != 0:
-        combined = f"{result.stderr}\n{result.stdout}"
-        if "500" in combined:
-            raise PushHTTP500Error(combined.strip())
+    if result.returncode != 0 and "500" in (result.stdout or ""):
+        raise PushHTTP500Error(result.stdout.strip())
     return result
 
 
@@ -334,7 +336,7 @@ def push_image(
         if result.returncode == 0:
             click.echo(f"Pushed {ft}")
             continue
-        combined_output = f"{result.stderr}\n{result.stdout}".strip()
+        combined_output = (result.stdout or "").strip()
         # Gitea #31964: push fails because tag already exists.
         # Delete the old manifest and retry once.
         if username and token and "already exists" in combined_output.lower():
@@ -350,14 +352,15 @@ def push_image(
             click.echo(f"  Retrying push {ft}...")
             result = subprocess.run(  # nosec B603
                 cmd,
-                capture_output=True,
+                stdout=subprocess.PIPE,
+                stderr=subprocess.STDOUT,
                 text=True,
                 check=False,
             )
             if result.returncode == 0:
                 click.echo(f"Pushed {ft} (after retry)")
                 continue
-            combined_output = f"{result.stderr}\n{result.stdout}".strip()
+            combined_output = (result.stdout or "").strip()
         click.echo(
             _("Push failed for {tag}: {error}", tag=ft, error=combined_output),
             err=True,