docs(api): describe the host access routes and keep them out of the MCP tools

Add the host access routes to the /api/instructions text of the add-ons
group. Add a spec that no MCP tool maps to them and that nothing under
pkg/mcp names them, so an agent cannot reach them through a tool.

Assisted-by: Claude:claude-sonnet-5-5 go gofmt ginkgo

pkg/mcp/localaitools/hostgrants_unmapped_test.go

@@ -0,0 +1,44 @@
+package localaitools
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+// The host access routes (/api/addons/host-grants) decide what an add-on may
+// ask the host to do. They accept only the administrator's own browser
+// session, so an agent or an MCP client, which holds a key or a tool session,
+// can never grant, revoke, deny or turn the blanket approval on. This spec
+// keeps that true: no tool maps to them, and nothing under pkg/mcp calls them.
+var _ = Describe("host access and the MCP tools", func() {
+	It("maps no tool to any /api/addons/host-grants route", func() {
+		for tool, route := range toolToHTTPRoute {
+			Expect(route).NotTo(ContainSubstring("host-grants"), tool)
+			Expect(route).NotTo(ContainSubstring("/api/addons"), tool+": add-on lifecycle and host access are not tools")
+		}
+	})
+
+	It("never names the routes in the code of the MCP server, its clients or its prompts", func() {
+		root := "."
+		var hits []string
+		Expect(filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
+			if err != nil || info.IsDir() || strings.HasSuffix(path, "_test.go") {
+				return err
+			}
+			b, rerr := os.ReadFile(path)
+			if rerr != nil {
+				return rerr
+			}
+			s := strings.ToLower(string(b))
+			if strings.Contains(s, "host-grants") || strings.Contains(s, "hostgrants") {
+				hits = append(hits, path)
+			}
+			return nil
+		})).To(Succeed())
+		Expect(hits).To(BeEmpty(), "an MCP tool or client must not reach the host access routes")
+	})
+})