diff --git a/docs/specs/DEVX-163.md b/docs/specs/DEVX-163.md
new file mode 100644
index 0000000..234a346
--- /dev/null
+++ b/docs/specs/DEVX-163.md
@@ -0,0 +1,33 @@
+# DEVX-163: Fix _run_push to check stdout for HTTP 500
+
+## Problem
+`_run_push` only checked `result.stderr` for HTTP 500, but docker push
+sends the "received unexpected HTTP status: 500 Internal Server Error"
+message to **stdout**, not stderr. This means the tenacity retry logic
+added in DEVX-162 never triggered — the push failed immediately without
+retrying.
+
+## Approach
+Check both `result.stdout` and `result.stderr` for the "500" status code.
+Also update the "already exists" check in `push_image` to check both
+streams, since docker may send that message to stdout as well.
+
+REQ-1: _run_push checks both stdout and stderr for HTTP 500
+REQ-2: push_image "already exists" check uses combined stdout+stderr
+REQ-3: All existing tests pass with 100% coverage
+
+## Test Plan
+- Unit tests for stdout 500 detection
+- Unit tests for stderr 500 detection
+- Manual: trigger build-images workflow and verify retry works
+
+## Deploy Plan
+- Merge to master
+
+## Rollback Plan
+- Revert the merge commit
+
+## Acceptance Criteria
+- [x] REQ-1: _run_push checks both stdout and stderr for HTTP 500
+- [x] REQ-2: push_image "already exists" check uses combined stdout+stderr
+- [x] REQ-3: All existing tests pass with 100% coverage
diff --git a/src/devx/tools/build_image.py b/src/devx/tools/build_image.py
index e1ec2a7..d04ec46 100644
--- a/src/devx/tools/build_image.py
+++ b/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
diff --git a/tests/unit/test_build_image.py b/tests/unit/test_build_image.py
index 0efc263..91ff082 100644
--- a/tests/unit/test_build_image.py
+++ b/tests/unit/test_build_image.py
@@ -288,7 +288,7 @@ class TestPushImage:
         """HTTP 500 from registry race condition — retry succeeds."""
         spec = ImageSpec(name="ci-base", dockerfile="Dockerfile", tags=["latest"])
         results = [
-            MagicMock(returncode=1, stderr="received unexpected HTTP status: 500 Internal Server Error", stdout=""),
+            MagicMock(returncode=1, stderr="", stdout="received unexpected HTTP status: 500 Internal Server Error"),
             MagicMock(returncode=0, stderr="", stdout=""),
         ]
         with (
@@ -303,7 +303,7 @@ class TestPushImage:
         """HTTP 500 retries exhausted — push fails, no delete attempted."""
         spec = ImageSpec(name="ci-base", dockerfile="Dockerfile", tags=["latest"])
         mock_result = MagicMock(
-            returncode=1, stderr="received unexpected HTTP status: 500 Internal Server Error", stdout=""
+            returncode=1, stderr="", stdout="received unexpected HTTP status: 500 Internal Server Error"
         )
         with (
             patch("devx.tools.build_image.subprocess.run", return_value=mock_result),
@@ -313,7 +313,7 @@ class TestPushImage:
             assert push_image(spec, "git.example.com", username="user", token="tok") is False
             mock_del.assert_not_called()
 
-    def test_run_push_raises_on_500(self) -> None:
+    def test_run_push_raises_on_500_stderr(self) -> None:
         """_run_push raises PushHTTP500Error when stderr contains 500."""
         from devx.tools.build_image import _run_push
 
@@ -322,6 +322,17 @@ class TestPushImage:
             with pytest.raises(PushHTTP500Error, match="HTTP 500"):
                 _run_push(["docker", "push", "img:latest"])
 
+    def test_run_push_raises_on_500_stdout(self) -> None:
+        """_run_push raises PushHTTP500Error when stdout contains 500 (docker sends to stdout)."""
+        from devx.tools.build_image import _run_push
+
+        mock_result = MagicMock(
+            returncode=1, stderr="", stdout="received unexpected HTTP status: 500 Internal Server Error"
+        )
+        with patch("devx.tools.build_image.subprocess.run", return_value=mock_result):
+            with pytest.raises(PushHTTP500Error, match="500"):
+                _run_push(["docker", "push", "img:latest"])
+
     def test_run_push_no_raise_on_non_500(self) -> None:
         """_run_push returns result when stderr has no 500."""
         from devx.tools.build_image import _run_push