test: harden jajce terrain navigation

docs/BUILD_IN_PUBLIC_PLAN.md

@@ -623,11 +623,16 @@ Completed:
 6. `JajceWorld` runtime integration with bindings and regression coverage.
 7. Bounded Jajce beauty baseline with six terrain layers, water, atmosphere,
    foliage motion, building blockouts, and smoke.
+8. Base Terrain3D collision/navigation guardrails: runtime tests now keep
+   Terrain3D collision enabled, keep the old greybox ground out of physics, and
+   verify required navigation paths track the authored height field.
 
 Next:
 
-1. Capture and visually review “Jajce Lookdev 01.”
-2. Add the cinematic/debug toggle and repeatable demo reset.
+1. Continue replacing the temporary greybox navigation source with baked
+   Terrain3D-derived navigation for the sculpted playable loop.
+
+2. Capture and visually review “Jajce Lookdev 01.”
 3. Capture “Simulation Garden 01.”
 
 Do not start with GIS data, a full city, a large asset pack, or more NPC

docs/LEARNING_ROADMAP.md

@@ -670,6 +670,10 @@ Recently completed:
 - Activity-site capacity enforcement for rest, study, and patrol target
   resolution, derived from NPC target claims rather than presentation-only
   counters.
+- Terrain3D collision/navigation hardening began: scaffold and runtime tests
+  now assert Terrain3D collision remains enabled, the hidden greybox ground no
+  longer provides physics collision, and tested navigation routes stay close to
+  the authored Terrain3D height field.
 
 This order strengthens the simulation while regularly producing visible
 progress suitable for public development updates.

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,