test: harden jajce terrain navigation

docs/PROJECT_CONTEXT.md

@@ -193,7 +193,8 @@ study, and patrol target typed activity sites. The migration is documented in
 - **Main scene:** `res://main.tscn`
 - **Terrain:** Terrain3D 1.0.2 is installed and enabled
 - **Jajce runtime:** reusable 512 m Terrain3D seed, greybox landmarks, stable
-  ResourceNode placement, lookdev camera, and tested runtime navigation
+  ResourceNode placement, lookdev camera, tested runtime navigation, and base
+  Terrain3D collision/navigation guardrails
 - **Terrain compatibility floor:** Godot 4.4 according to the bundled extension
 - **Version control:** Git
 - **Primary branch:** `main`
@@ -328,6 +329,9 @@ distance with resource `safety_risk`, `comfort_distance`, and
 - eight ResourceNodes preserving stable food/wood discovery IDs;
 - typed village pantry storage and typed guard, study, and rest activity sites;
 - a temporary baked navigation loop with 24 tested routes;
+- base collision/navigation guardrails that keep Terrain3D collision enabled,
+  keep the hidden greybox ground out of runtime physics, and compare required
+  navigation paths against the Terrain3D height field;
 - a look-development scene and camera.
 
 This is a runtime integration proof, not the final terrain composition.
@@ -534,6 +538,9 @@ These are expected prototype constraints, not necessarily isolated bugs:
   mutation APIs, but selection, execution, target resolution, and active-world
   queries now have focused collaborators.
 - Path failure and interruption emit a `navigation_failed` signal and send the NPC to wander; this is functional but not yet polished.
+- The old greybox navigation source remains temporary; current tests now guard
+  against collision/nav regressions, but the next terrain base phase is a
+  Terrain3D-derived bake for the sculpted playable loop.
 - Terrain3D and the bounded Jajce beauty baseline now run in the main game
   scene; final visual review and character/profession readability remain.
 - Combat, companions, factions, politics, trade, rumours, quests, persistence,