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/cron/service.go

@@ -340,7 +340,7 @@ func (cs *CronService) saveStoreUnsafe() error {
 		return err
 	}
 
-	return os.WriteFile(cs.storePath, data, 0644)
+	return os.WriteFile(cs.storePath, data, 0600)
 }
 
 func (cs *CronService) AddJob(name string, schedule CronSchedule, message string, deliver bool, channel, to string) (*CronJob, error) {

pkg/cron/service_test.go

@@ -0,0 +1,38 @@
+package cron
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+)
+
+func TestSaveStore_FilePermissions(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("file permission bits are not enforced on Windows")
+	}
+
+	tmpDir := t.TempDir()
+	storePath := filepath.Join(tmpDir, "cron", "jobs.json")
+
+	cs := NewCronService(storePath, nil)
+
+	_, err := cs.AddJob("test", CronSchedule{Kind: "every", EveryMS: int64Ptr(60000)}, "hello", false, "cli", "direct")
+	if err != nil {
+		t.Fatalf("AddJob failed: %v", err)
+	}
+
+	info, err := os.Stat(storePath)
+	if err != nil {
+		t.Fatalf("Stat failed: %v", err)
+	}
+
+	perm := info.Mode().Perm()
+	if perm != 0600 {
+		t.Errorf("cron store has permission %04o, want 0600", perm)
+	}
+}
+
+func int64Ptr(v int64) *int64 {
+	return &v
+}