feat: add PermissionCache for exec tool permission system

pkg/tools/permission.go

@@ -0,0 +1,48 @@
+package tools
+
+import (
+	"sync"
+)
+
+type PermissionCache struct {
+	mu    sync.RWMutex
+	perms map[string]string // path → "once"|"session"|"denied"
+}
+
+func NewPermissionCache() *PermissionCache {
+	return &PermissionCache{
+		perms: make(map[string]string),
+	}
+}
+
+// Check returns "once", "session", "denied", or "" (no permission)
+func (pc *PermissionCache) Check(path string) string {
+	pc.mu.RLock()
+	defer pc.mu.RUnlock()
+	
+	// Check exact match
+	if val, ok := pc.perms[path]; ok {
+		return val
+	}
+	
+	// Check if any parent path is granted "session"
+	for cachedPath, val := range pc.perms {
+		if val == "session" && len(cachedPath) < len(path) && path[:len(cachedPath)] == cachedPath {
+			return "session"
+		}
+	}
+	
+	return ""
+}
+
+func (pc *PermissionCache) Grant(path, duration string) {
+	pc.mu.Lock()
+	defer pc.mu.Unlock()
+	pc.perms[path] = duration
+}
+
+func (pc *PermissionCache) Revoke(path string) {
+	pc.mu.Lock()
+	defer pc.mu.Unlock()
+	delete(pc.perms, path)
+}

pkg/tools/permission_test.go

@@ -0,0 +1,13 @@
+package tools
+
+import (
+	"testing"
+)
+
+func TestPermissionCache_Check_NoPermission(t *testing.T) {
+	pc := NewPermissionCache()
+	result := pc.Check("/desktop")
+	if result != "" {
+		t.Errorf("Expected empty string, got %s", result)
+	}
+}