As usual, the Cool VL Viewer is the first v1-UI viewer to provide you with the newest features backported from the v3 viewer (and even not all v3-based TPVs are providing those features !).
The pathfinding/navmesh tools have been fully implemented into the Cool VL Viewer v1.26.4.25 and v1.26.5.4, with the exception of the navmesh rendering (that depends on a closed source library based off Havok's).
The viewer can now send rebake requests to a region; when such a rebake is needed, a "dirty navmesh" icon (see the attached picture below) appears in the status bar and if you can build in that rergion a "Rebake Region" button appears in the overlay bar.
Two floaters were added, that you can open from the "Tools" menu: the "Pathfinding Characters" floater and the "Pathfinding Linksets" floater. They are the same floaters as the ones found in the v3.4 viewer, with the exception of the missing "Physics capsule" check box in the "Pathfinding Characters" floater (the Havok library being needed to render these "capsules").
Note that the backported code was also hardened against bogus server messages (that the original code simply 'dealt' with by voluntarily crashing the viewer !), with proper warnings in the log and adequate fall through code to avoid crashes or other dire consequences.
Enjoy !