boxcli: fix VS Code binary path resolution on macOS (#2806)

## Summary

The WSL fix in #2729 (4ba6fce) broke "Reopen in Devbox shell
environment" on macOS.

That commit constructs the VS Code binary path as
`$VSCODE_CWD/bin/code`. On WSL, `VSCODE_CWD` points to the VS Code
installation directory (e.g., `/mnt/c/.../Microsoft VS Code`), so this
works correctly. On macOS however, `VSCODE_CWD` is set to the workspace
directory, producing a path like `/Users/user/my-project/bin/code` —
which doesn't exist:

e.g. The debug logs on my machine gives:

```
fork/exec /Users/josh/src/my-project/bin/code: no such file or directory
```

This PR adds an os.Stat check so the constructed path is only used when
the binary actually exists there, falling back to the bare command name
(resolved via `PATH`) otherwise. The resolution logic is extracted into
a `resolveEditorBinary` function with unit tests covering:

- `VSCODE_CWD` unset → uses bare name
- `VSCODE_CWD` points to a VS Code installation (WSL) → uses full path
- `VSCODE_CWD` points to a workspace directory (macOS) → falls back to
bare name

## How was it tested?

- Unit tests for `resolveEditorBinary` covering all three scenarios
- `go test -race -cover ./internal/boxcli/` passes
- `golangci-lint run ./internal/boxcli/` passes

## Community Contribution License

All community contributions in this pull request are licensed to the
project
maintainers under the terms of the
[Apache 2 License](https://www.apache.org/licenses/LICENSE-2.0).

By creating this pull request, I represent that I have the right to
license the
contributions to the project maintainers under the Apache 2 License as
stated in
the
[Community Contribution
License](https://github.com/jetify-com/opensource/blob/main/CONTRIBUTING.md#community-contribution-license).

Co-authored-by: Josh Godsiff <josh.godsiff@corro.co>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 3 people

internal/boxcli/integrate.go

@@ -124,12 +124,7 @@ func runIntegrateVSCodeCmd(cmd *cobra.Command, flags integrateCmdFlags) error {
 		return err
 	}
 	// Open editor with devbox shell environment
-	cmndName := flags.ideName
-	cwd, ok := os.LookupEnv("VSCODE_CWD")
-	if ok {
-		// Specify full path to avoid running the `code` shell script from VS Code Server, which fails under WSL
-		cmndName = cwd + "/bin/" + cmndName
-	}
+	cmndName := resolveEditorBinary(flags.ideName)
 	cmnd := exec.Command(cmndName, message.ConfigDir)
 	cmnd.Env = append(cmnd.Env, envVars...)
 	var outb, errb bytes.Buffer
@@ -145,6 +140,23 @@ func runIntegrateVSCodeCmd(cmd *cobra.Command, flags integrateCmdFlags) error {
 	return nil
 }
 
+// resolveEditorBinary returns the path to the editor binary. On WSL,
+// VSCODE_CWD points to the VS Code installation directory, so we can
+// construct an absolute path to avoid the VS Code Server shell script.
+// On macOS, VSCODE_CWD is the workspace directory, so the constructed
+// path won't exist and we fall back to the bare command name.
+func resolveEditorBinary(ideName string) string {
+	cwd, ok := os.LookupEnv("VSCODE_CWD")
+	if !ok {
+		return ideName
+	}
+	fullPath := cwd + "/bin/" + ideName
+	if _, err := os.Stat(fullPath); err == nil {
+		return fullPath
+	}
+	return ideName
+}
+
 type debugMode struct {
 	enabled bool
 }

internal/boxcli/integrate_test.go

@@ -0,0 +1,77 @@
+// Copyright 2024 Jetify Inc. and contributors. All rights reserved.
+// Use of this source code is governed by the license in the LICENSE file.
+
+package boxcli
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestResolveEditorBinary(t *testing.T) {
+	// Create a temp directory with a bin/code binary to simulate
+	// a VS Code installation (e.g., WSL's VSCODE_CWD).
+	installDir := t.TempDir()
+	binDir := filepath.Join(installDir, "bin")
+	if err := os.MkdirAll(binDir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	codePath := filepath.Join(binDir, "code")
+	if err := os.WriteFile(codePath, []byte("#!/bin/sh\n"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+
+	// A directory that does NOT contain bin/code, simulating
+	// macOS where VSCODE_CWD is the workspace directory.
+	workspaceDir := t.TempDir()
+
+	tests := []struct {
+		name      string
+		vscodeCWD string // empty means unset
+		ideName   string
+		want      string
+	}{
+		{
+			name:    "VSCODE_CWD unset falls back to bare name",
+			ideName: "code",
+			want:    "code",
+		},
+		{
+			name:      "VSCODE_CWD with valid binary uses full path",
+			vscodeCWD: installDir,
+			ideName:   "code",
+			want:      filepath.Join(installDir, "bin", "code"),
+		},
+		{
+			name:      "VSCODE_CWD without binary falls back to bare name",
+			vscodeCWD: workspaceDir,
+			ideName:   "code",
+			want:      "code",
+		},
+		{
+			name:      "non-default IDE name resolves correctly",
+			vscodeCWD: workspaceDir,
+			ideName:   "cursor",
+			want:      "cursor",
+		},
+	}
+
+	for _, testCase := range tests {
+		t.Run(testCase.name, func(t *testing.T) {
+			if testCase.vscodeCWD != "" {
+				t.Setenv("VSCODE_CWD", testCase.vscodeCWD)
+			} else {
+				os.Unsetenv("VSCODE_CWD")
+			}
+
+			got := resolveEditorBinary(testCase.ideName)
+			if got != testCase.want {
+				t.Errorf(
+					"resolveEditorBinary(%q) = %q, want %q",
+					testCase.ideName, got, testCase.want,
+				)
+			}
+		})
+	}
+}