Hi Jeff:
Because of the reaction issues (amongst other reasons), MFMP has gone to a rather thicker steel metallic capsule to contain the solid part of the fuel (see the GlowStick 5 Run). The higher temp reaction/breakdowns of LAH[:Li] can get rather complicated, and I am sure that others will comment about this in further detail. It is believed that Rossi has/had used a metallic containment system for the fuel, and Parkhomov used a Stainless Steel Sleeve to facilitate transferring fuel to the heating tubes, but it may have also aided in protecting the tube for a period of time.
I think you are probably aware of most of this, but I thought I would hash over it as a starting point in this discussion. MFMP hasn't loaded additional Li yet, but that may happen soon. This is when the thicker metallic capsule will really be tested against additional Li. Since Gas Exchange is promoted via the MFMP capsule design, there is really nothing preventing liquid phase fuel from escaping the capsule, just slowing that eventual process down.
... If you have some better design ideas on a containment system, I am sure all of us would like to hear!