fix: tighten file perms and enforce Slack ACL checks (#186)

- write config and cron store with 0600 instead of 0644
- check allow list in Slack slash commands and app mentions
- pass workspace restrict flag to cron exec tool

Closes #179

pkg/config/config.go

@@ -370,7 +370,7 @@ func SaveConfig(path string, cfg *Config) error {
 		return err
 	}
 
-	return os.WriteFile(path, data, 0644)
+	return os.WriteFile(path, data, 0600)
 }
 
 func (c *Config) WorkspacePath() string {

pkg/config/config_test.go

@@ -1,6 +1,9 @@
 package config
 
 import (
+	"os"
+	"path/filepath"
+	"runtime"
 	"testing"
 )
 
@@ -147,6 +150,30 @@ func TestDefaultConfig_WebTools(t *testing.T) {
 	}
 }
 
+func TestSaveConfig_FilePermissions(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("file permission bits are not enforced on Windows")
+	}
+
+	tmpDir := t.TempDir()
+	path := filepath.Join(tmpDir, "config.json")
+
+	cfg := DefaultConfig()
+	if err := SaveConfig(path, cfg); err != nil {
+		t.Fatalf("SaveConfig failed: %v", err)
+	}
+
+	info, err := os.Stat(path)
+	if err != nil {
+		t.Fatalf("Stat failed: %v", err)
+	}
+
+	perm := info.Mode().Perm()
+	if perm != 0600 {
+		t.Errorf("config file has permission %04o, want 0600", perm)
+	}
+}
+
 // TestConfig_Complete verifies all config fields are set
 func TestConfig_Complete(t *testing.T) {
 	cfg := DefaultConfig()