Add more context to the shim delete error

When a shim delete hits a timeout, currently the error message does not
indicate that the delete was killed rather than failed to complete.

Signed-off-by: Derek McGowan <derek@mcg.dev>

core/runtime/v2/binary.go

@@ -116,7 +116,7 @@ func (b *binary) Start(ctx context.Context, opts *types.Any, onClose func()) (_
 	}()
 	out, err := cmd.CombinedOutput()
 	if err != nil {
-		return nil, fmt.Errorf("%s: %w", out, err)
+		return nil, shimCallError(ctx.Err(), out, err)
 	}
 	onCloseWithShimLog := func() {
 		onClose()
@@ -191,11 +191,12 @@ func (b *binary) Delete(ctx context.Context) (*runtime.Exit, error) {
 	cmd.Stderr = errb
 	if err := cmd.Run(); err != nil {
 		log.G(ctx).WithFields(log.Fields{
-			"cmd":   cmd.String(),
-			"error": err,
-			"id":    b.bundle.ID,
+			"cmd":    cmd.String(),
+			"error":  err,
+			"id":     b.bundle.ID,
+			"stderr": errb.String(),
 		}).Error("failed to delete dead shim")
-		return nil, fmt.Errorf("%s: %w", errb.String(), err)
+		return nil, shimCallError(ctx.Err(), errb.Bytes(), err)
 	}
 	if s := errb.String(); s != "" {
 		log.G(ctx).WithFields(log.Fields{
@@ -216,3 +217,23 @@ func (b *binary) Delete(ctx context.Context) (*runtime.Exit, error) {
 		Pid:       response.Pid,
 	}, nil
 }
+
+// shimCallError builds an error for a failed shim binary invocation.
+//
+// client.Command is run via exec.CommandContext, which kills the process
+// once ctx is done. On Windows that kill is TerminateProcess(handle, 1),
+// which is indistinguishable from the shim genuinely calling os.Exit(1),
+// and os/exec reports the wait status in preference to the context error.
+// A killed shim also writes nothing to stderr, so without surfacing ctxErr
+// the resulting message degenerates to ": exit status 1" with no
+// indication that containerd killed the process rather than the shim
+// exiting on its own.
+func shimCallError(ctxErr error, stderr []byte, err error) error {
+	if ctxErr != nil {
+		err = fmt.Errorf("shim killed after %w: %w", ctxErr, err)
+	}
+	if s := bytes.TrimSpace(stderr); len(s) > 0 {
+		err = fmt.Errorf("%s: %w", s, err)
+	}
+	return err
+}