fix(sessionservice): include subprocess stderr in FAILED lifecycle_detail

src/panopticon/sessionservice/local_runner.py

@@ -61,7 +61,14 @@ def _subprocess_run(args: Sequence[str], *, check: bool = True, interactive: boo
     if interactive or verbose:  # inherit streams: TTY attachment (interactive) or visible build output (verbose)
         subprocess.run(list(args), check=check)
         return ""
-    return subprocess.run(list(args), check=check, capture_output=True, text=True).stdout
+    try:
+        return subprocess.run(list(args), check=check, capture_output=True, text=True).stdout
+    except subprocess.CalledProcessError as exc:
+        stderr = (exc.stderr or "").strip()
+        msg = f"Command '{exc.cmd[0]}' exited {exc.returncode}"
+        if stderr:
+            msg += f": {stderr}"
+        raise RuntimeError(msg) from exc
 
 
 

tests/test_local_runner.py

@@ -13,7 +13,7 @@
 import pytest
 
 from panopticon.core.models import LifecyclePhase
-from panopticon.sessionservice.local_runner import LocalRunner
+from panopticon.sessionservice.local_runner import LocalRunner, _subprocess_run
 from panopticon.sessionservice.runner import Runner
 
 
@@ -235,6 +235,33 @@ def test_tmux_socket_can_be_overridden() -> None:
     assert rec.calls[3][0][:4] == ["tmux", "-L", "panopt", "new-session"]  # kill-session, rm, run, tmux
 
 
+# -- _subprocess_run error surfacing -------------------------------------------------
+
+
+def test_subprocess_run_includes_stderr_in_error(monkeypatch: pytest.MonkeyPatch) -> None:
+    """CalledProcessError.stderr is surfaced in the RuntimeError message."""
+    err = subprocess.CalledProcessError(125, ["docker", "run"], stderr="no such image: panopticon-foo")
+
+    def _failing_run(*args: object, **kwargs: object) -> subprocess.CompletedProcess[str]:
+        raise err
+
+    monkeypatch.setattr(subprocess, "run", _failing_run)
+    with pytest.raises(RuntimeError, match="no such image: panopticon-foo"):
+        _subprocess_run(["docker", "run", "panopticon-foo"])
+
+
+def test_subprocess_run_error_without_stderr(monkeypatch: pytest.MonkeyPatch) -> None:
+    """CalledProcessError with no stderr still raises RuntimeError with exit code."""
+    err = subprocess.CalledProcessError(1, ["docker", "build"], stderr="")
+
+    def _failing_run(*args: object, **kwargs: object) -> subprocess.CompletedProcess[str]:
+        raise err
+
+    monkeypatch.setattr(subprocess, "run", _failing_run)
+    with pytest.raises(RuntimeError, match=r"Command 'docker' exited 1$"):
+        _subprocess_run(["docker", "build", "."])
+
+
 # -- integration: real docker + tmux ------------------------------------------------
 
 _HAVE_DOCKER_TMUX = bool(shutil.which("docker") and shutil.which("tmux"))