fix(mcp): unified grant revocation with per-agent tool group isolation

- Add GrantChecker interface with cache + event-bus invalidation for revalidating MCP tool grants at execution time (not just dispatch)
- Move toolGroups from package-level global to per-Registry field; Clone() gives each agent Loop isolated tool groups, eliminating cross-agent race condition
- BridgeTool.Execute rechecks grant validity before executing MCP methods; uses serverID field for cache key
- Wire MCPGrantChecker through ResolverDeps to MCP Manager and LoopConfig
- Add integration test for grant revocation scenarios
- Update policy functions to accept *Registry parameter

internal/http/skills_import.go

@@ -15,6 +15,7 @@ import (
 	"github.com/nextlevelbuilder/goclaw/internal/bus"
 	"github.com/nextlevelbuilder/goclaw/internal/config"
 	"github.com/nextlevelbuilder/goclaw/internal/i18n"
+	"github.com/nextlevelbuilder/goclaw/internal/skills"
 	"github.com/nextlevelbuilder/goclaw/internal/store"
 	"github.com/nextlevelbuilder/goclaw/internal/store/pg"
 )
@@ -132,6 +133,19 @@ func (h *SkillsHandler) doSkillsImport(ctx context.Context, r io.Reader, userID
 			continue
 		}
 
+		// Security guard: scan SKILL.md for malicious content BEFORE any disk/DB write
+		if entry.skillMD != nil {
+			violations, safe := skills.GuardSkillContent(string(entry.skillMD))
+			if !safe {
+				slog.Warn("security.skills.import_rejected",
+					"slug", slug,
+					"violations", len(violations),
+					"first_rule", violations[0].Reason)
+				summary.SkillsSkipped++
+				continue
+			}
+		}
+
 		var meta struct {
 			Name        string   `json:"name"`
 			Slug        string   `json:"slug"`

internal/http/skills_upload.go

@@ -106,6 +106,20 @@ func (h *SkillsHandler) handleUpload(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Security guard: scan for malicious content BEFORE any disk/DB write
+	violations, safe := skills.GuardSkillContent(skillContent)
+	if !safe {
+		slog.Warn("security.skills.upload_rejected",
+			"user_id", userID,
+			"violations", len(violations),
+			"first_rule", violations[0].Reason)
+		writeJSON(w, http.StatusBadRequest, map[string]any{
+			"error":      i18n.T(locale, i18n.MsgInvalidRequest, "skill content failed security scan"),
+			"violations": skills.FormatGuardViolations(violations),
+		})
+		return
+	}
+
 	name, description, slug, frontmatter := skills.ParseSkillFrontmatter(skillContent)
 	if name == "" {
 		writeJSON(w, http.StatusBadRequest, map[string]string{"error": i18n.T(locale, i18n.MsgRequired, "name in SKILL.md frontmatter")})