fix: normalize relative path env vars and isolate copilot config

- Resolve path-valued env vars (GOOGLE_APPLICATION_CREDENTIALS,
  CURL_CA_BUNDLE) to absolute paths in cleanEnv() so they remain
  valid when subprocesses run from os.TempDir()
- Use --config-dir with a temporary empty directory for copilot to
  prevent user-configured MCP servers in ~/.copilot/ from loading
- Add TestCleanEnv_NormalizesRelativePaths regression test

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: wesm

internal/insight/generate.go

@@ -8,6 +8,7 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"strings"
 )
 
@@ -148,17 +149,35 @@ func envKeyAllowed(key string) bool {
 	return false
 }
 
+// pathValuedKeys lists env var keys whose values are file
+// paths. These must be resolved to absolute paths before
+// passing to subprocesses that run in a different directory.
+var pathValuedKeys = map[string]bool{
+	"GOOGLE_APPLICATION_CREDENTIALS": true,
+	"CURL_CA_BUNDLE":                 true,
+}
+
 // cleanEnv returns an allowlisted subset of the current
 // environment for agent CLI subprocesses, plus
-// CLAUDE_NO_SOUND=1.
+// CLAUDE_NO_SOUND=1. Path-valued env vars are resolved to
+// absolute paths so they remain valid when the subprocess
+// runs from a different working directory.
 func cleanEnv() []string {
 	env := os.Environ()
 	filtered := make([]string, 0, len(env))
 	for _, e := range env {
-		k, _, _ := strings.Cut(e, "=")
-		if envKeyAllowed(k) {
-			filtered = append(filtered, e)
+		k, v, _ := strings.Cut(e, "=")
+		if !envKeyAllowed(k) {
+			continue
+		}
+		if pathValuedKeys[strings.ToUpper(k)] &&
+			v != "" && !filepath.IsAbs(v) {
+			abs, err := filepath.Abs(v)
+			if err == nil {
+				e = k + "=" + abs
+			}
 		}
+		filtered = append(filtered, e)
 	}
 	return append(filtered, "CLAUDE_NO_SOUND=1")
 }
@@ -459,16 +478,27 @@ func parseCodexStream(
 // generateCopilot invokes `copilot -p <prompt> --silent`.
 // The prompt is passed as the -p argument (copilot does not
 // read prompts from stdin). Output is plain text on stdout.
+// An empty --config-dir isolates copilot from user-configured
+// MCP servers in ~/.copilot/.
 func generateCopilot(
 	ctx context.Context, path, prompt string, onLog LogFunc,
 ) (Result, error) {
+	configDir, err := os.MkdirTemp("", "copilot-insight-*")
+	if err != nil {
+		return Result{}, fmt.Errorf(
+			"create copilot config dir: %w", err,
+		)
+	}
+	defer os.RemoveAll(configDir)
+
 	cmd := exec.CommandContext(
 		ctx, path,
 		"-p", prompt,
 		"--silent",
 		"--no-custom-instructions",
 		"--no-ask-user",
 		"--disable-builtin-mcps",
+		"--config-dir", configDir,
 	)
 	cmd.Dir = os.TempDir()
 	cmd.Env = cleanEnv()

internal/insight/generate_test.go

@@ -228,6 +228,44 @@ func TestCleanEnv(t *testing.T) {
 	}
 }
 
+func TestCleanEnv_NormalizesRelativePaths(t *testing.T) {
+	t.Setenv("GOOGLE_APPLICATION_CREDENTIALS", "creds/svc.json")
+	t.Setenv("CURL_CA_BUNDLE", "certs/ca.pem")
+
+	env := cleanEnv()
+	envMap := make(map[string]string, len(env))
+	for _, e := range env {
+		k, v, _ := strings.Cut(e, "=")
+		envMap[strings.ToUpper(k)] = v
+	}
+
+	cwd, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, key := range []string{
+		"GOOGLE_APPLICATION_CREDENTIALS",
+		"CURL_CA_BUNDLE",
+	} {
+		v, ok := envMap[key]
+		if !ok {
+			t.Fatalf("%s missing from env", key)
+		}
+		if !filepath.IsAbs(v) {
+			t.Errorf(
+				"%s = %q, want absolute path", key, v,
+			)
+		}
+		if !strings.HasPrefix(v, cwd) {
+			t.Errorf(
+				"%s = %q, want prefix %q",
+				key, v, cwd,
+			)
+		}
+	}
+}
+
 func TestEnvKeyAllowed(t *testing.T) {
 	tests := []struct {
 		key  string
@@ -472,21 +510,20 @@ func TestGenerateCopilot_CLIFlags(t *testing.T) {
 		strings.TrimSpace(string(argsData)), "\n",
 	)
 
-	wantArgs := []string{
-		"-p", "test prompt",
+	// --config-dir value is a dynamic temp path, so verify
+	// args as a joined string for the fixed flags.
+	joined := strings.Join(args, " ")
+	for _, want := range []string{
+		"-p test prompt",
 		"--silent",
 		"--no-custom-instructions",
 		"--no-ask-user",
 		"--disable-builtin-mcps",
-	}
-	if len(args) != len(wantArgs) {
-		t.Fatalf("args = %v, want %v", args, wantArgs)
-	}
-	for i, want := range wantArgs {
-		if args[i] != want {
+		"--config-dir",
+	} {
+		if !strings.Contains(joined, want) {
 			t.Errorf(
-				"arg[%d] = %q, want %q",
-				i, args[i], want,
+				"args %q missing %q", joined, want,
 			)
 		}
 	}