diff --git a/internal/cli/run.go b/internal/cli/run.go
index d621a00d87..7f6a0d460e 100644
--- a/internal/cli/run.go
+++ b/internal/cli/run.go
@@ -957,7 +957,7 @@ func bootstrapEnv(sandboxName, repoDir string, h *harness.Harness) error {
 	}
 	tmpFile.Close()
 
-	if err := sandbox.Upload(sandboxName, tmpFile.Name(), remoteEnvFile); err != nil {
+	if err := sandbox.UploadFile(sandboxName, tmpFile.Name(), remoteEnvFile); err != nil {
 		return fmt.Errorf("copying .env file to sandbox: %w", err)
 	}
 
@@ -998,13 +998,13 @@ func bootstrapEnv(sandboxName, repoDir string, h *harness.Harness) error {
 			}
 			tmp.Close()
 
-			if err := sandbox.Upload(sandboxName, tmp.Name(), hf.Dest); err != nil {
+			if err := sandbox.UploadFile(sandboxName, tmp.Name(), hf.Dest); err != nil {
 				os.Remove(tmp.Name())
 				return fmt.Errorf("copying expanded file %s to %s: %w", hf.Src, hf.Dest, err)
 			}
 			os.Remove(tmp.Name())
 		} else {
-			if err := sandbox.Upload(sandboxName, hostPath, hf.Dest); err != nil {
+			if err := sandbox.UploadFile(sandboxName, hostPath, hf.Dest); err != nil {
 				return fmt.Errorf("copying host file %s to %s: %w", hf.Src, hf.Dest, err)
 			}
 		}
diff --git a/internal/sandbox/sandbox.go b/internal/sandbox/sandbox.go
index 1df64674af..b24f8a3b2c 100644
--- a/internal/sandbox/sandbox.go
+++ b/internal/sandbox/sandbox.go
@@ -377,6 +377,35 @@ func Upload(sandboxName, localPath, remotePath string) error {
 	return nil
 }
 
+// UploadFile copies a single local file into a sandbox at a specific remote path.
+// openshell sandbox upload treats the remote path as a directory (similar to
+// docker cp), placing the file inside it with the source basename. This function
+// uploads to the parent directory and renames inside the sandbox if the resulting
+// filename differs from the desired remote name, ensuring file-to-file semantics.
+// This mirrors the DownloadFile approach.
+func UploadFile(sandboxName, localPath, remotePath string) error {
+	remoteDir := filepath.Dir(remotePath)
+
+	if err := Upload(sandboxName, localPath, remoteDir); err != nil {
+		return err
+	}
+
+	// openshell places the file as <remoteDir>/<basename(localPath)>.
+	// If that differs from the desired remotePath, rename it in-sandbox.
+	uploadedPath := filepath.Join(remoteDir, filepath.Base(localPath))
+	if uploadedPath != remotePath {
+		mvCmd := fmt.Sprintf("mv %s %s", uploadedPath, remotePath)
+		_, stderr, exitCode, err := Exec(sandboxName, mvCmd, 10*time.Second)
+		if err != nil {
+			return fmt.Errorf("renaming uploaded file in sandbox %q: %w", sandboxName, err)
+		}
+		if exitCode != 0 {
+			return fmt.Errorf("renaming uploaded file in sandbox %q: exit %d: %s", sandboxName, exitCode, stderr)
+		}
+	}
+	return nil
+}
+
 // UploadDir uploads a local directory into a sandbox, preserving symlinks.
 // openshell sandbox upload dereferences symlinks; this builds a local tarball
 // with --no-dereference, uploads it, and extracts it in the sandbox.
diff --git a/internal/sandbox/sandbox_test.go b/internal/sandbox/sandbox_test.go
index 990fa49336..c0792bd08d 100644
--- a/internal/sandbox/sandbox_test.go
+++ b/internal/sandbox/sandbox_test.go
@@ -378,6 +378,17 @@ func TestEffectiveReadyTimeout_EnvVarCappedAtMax(t *testing.T) {
 	assert.Equal(t, maxReadyTimeout, got)
 }
 
+func TestUploadFile_OpenshellNotInPath(t *testing.T) {
+	tmp := t.TempDir()
+	f := filepath.Join(tmp, "test.txt")
+	require.NoError(t, os.WriteFile(f, []byte("hello"), 0o644))
+
+	t.Setenv("PATH", "")
+
+	err := UploadFile("test-sandbox", f, "/tmp/workspace/test.txt")
+	assert.Error(t, err)
+}
+
 func TestUploadDir_OpenshellNotInPath(t *testing.T) {
 	dir := t.TempDir()
 	t.Setenv("PATH", "")