Add L0-L4 security clearance for fleet commands and AI elevation.

Gate manual and AI commands by per-agent clearance, auto-elevate stuck hosts to L4 when AI mode allows, and surface clearance in Access Depth and LOTL timeline.

server/internal/clearance/clearance_test.go

@@ -0,0 +1,46 @@
+package clearance
+
+import (
+	"testing"
+)
+
+func TestL2AgentCannotExecShellWithoutElevation(t *testing.T) {
+	const agentClearance = L2
+
+	cases := []struct {
+		cmdType string
+		args    map[string]interface{}
+	}{
+		{"exec_shell", nil},
+		{"agent_command", map[string]interface{}{"action": "exec"}},
+		{"agent_command", map[string]interface{}{"action": "powershell"}},
+	}
+
+	for _, tc := range cases {
+		if err := EnforceClearance(tc.cmdType, tc.args, agentClearance); err == nil {
+			t.Fatalf("expected clearance error for %s %+v at L2", tc.cmdType, tc.args)
+		}
+	}
+
+	if err := EnforceClearance("discover_and_join", nil, agentClearance); err != nil {
+		t.Fatalf("L2 should allow spread: %v", err)
+	}
+	if err := EnforceAction("exec", agentClearance); err == nil {
+		t.Fatal("L2 should block exec action")
+	}
+	if err := EnforceAction("pause", agentClearance); err != nil {
+		t.Fatalf("L2 should allow pause: %v", err)
+	}
+}
+
+func TestCommandRequiredLevels(t *testing.T) {
+	if CommandRequiredLevel("restart_mining", nil) != L1 {
+		t.Fatal("restart_mining should be L1")
+	}
+	if CommandRequiredLevel("spread_now", nil) != L2 {
+		t.Fatal("spread_now should be L2")
+	}
+	if CommandRequiredLevel("set_agent_version", nil) != L4 {
+		t.Fatal("set_agent_version should be L4")
+	}
+}