feat(ui): add transient loading indicator

Reviewed-on: #11

README.md

@@ -152,6 +152,7 @@ WS  ws://localhost:8000/ws
 | `docs/technical/zustand.md`             | Game, settings, and subtitle stores                        |
 | `docs/technical/three-debugging.md`     | DevTools workflow for stepping into Three.js internals     |
 | `docs/technical/map-performance.md`     | Map draw-call bottlenecks and optimization notes           |
+| `docs/technical/map-lod.md`             | Runtime map LOD presets, paths, and workflow               |
 | `docs/technical/editor.md`              | Editor implementation details                              |
 | `docs/technical/animation.md`           | Animated, explodable, and reusable 3D model components     |
 | `docs/user/features.md`                 | Implemented feature inventory                              |

docs/technical/map-lod.md

@@ -0,0 +1,119 @@
+# Map LOD System
+
+This document describes the runtime LOD system used by the production map.
+
+## Goal
+
+The map now supports two visual versions for selected models:
+
+- the regular model in `public/models/<name>/`
+- the lighter model in `public/models/<name>-LOD/`
+
+The runtime chooses between those paths from the active graphics preset. This keeps nearby objects visually richer while reducing the cost of distant objects.
+
+## Graphics Presets
+
+Presets are configured in:
+
+```txt
+src/data/world/graphicsConfig.ts
+```
+
+Current behavior:
+
+| Preset   | Chunk load distance | Fog | LOD behavior                          |
+| -------- | ------------------: | --- | ------------------------------------- |
+| `low`    |                 10m | On  | Always use `*-LOD` models             |
+| `medium` |                 20m | On  | Always use `*-LOD` models             |
+| `high`   | Current default 50m | Off | Regular model up to 10m, then `*-LOD` |
+| `ultra`  |                 50m | Off | Regular model up to 20m, then `*-LOD` |
+
+The unload distance stays slightly larger than the load distance to avoid rapid mount/unmount flickering when the player stands near a boundary.
+
+## Runtime Selection
+
+LOD path mapping lives in:
+
+```txt
+src/data/world/mapLodConfig.ts
+```
+
+The main selector is `selectMapModelPathByDistance()`. It receives:
+
+- the current camera distance
+- the map model name
+- the regular model path
+- the active graphics preset
+
+It returns either the regular path or the `*-LOD` path.
+
+## Chunked Instanced Models
+
+Repeated static assets are rendered through:
+
+```txt
+src/world/map-instancing/MapInstancingSystem.tsx
+```
+
+For each visible chunk, the system checks the nearest instance in that chunk. If the nearest instance is inside the high-detail threshold, the whole chunk uses the regular model. Otherwise, it uses the `*-LOD` model.
+
+This is intentionally chunk-level LOD instead of per-instance LOD. It matches the existing chunk streaming architecture and avoids splitting every object into many tiny batches.
+
+## Single And Generated Models
+
+Single map nodes use:
+
+```txt
+src/hooks/world/useMapLodModelPath.ts
+src/world/GameMap.tsx
+```
+
+Some named map objects are rendered through dedicated generated components instead of the generic `GameMap` path. Those components must call `useMapLodModelPath()` directly.
+
+Current dedicated generated components with LOD support:
+
+```txt
+src/components/three/world/EcoleModel.tsx
+src/components/three/world/LaFabrikMapModel.tsx
+```
+
+This matters for `lafabrik`: adding `public/models/lafabrik-LOD/` is not enough by itself. The component must also be connected to `useMapLodModelPath()`.
+
+## Adding A New LOD Model
+
+To add LOD support for a model:
+
+1. Add the light model in `public/models/<name>-LOD/model.gltf`.
+2. Keep the regular model in `public/models/<name>/model.glb` or `public/models/<name>/model.gltf`.
+3. Add the mapping in `src/data/world/mapLodConfig.ts`.
+4. If the model uses a dedicated component, call `useMapLodModelPath()` in that component.
+5. Preload both paths when the component is dedicated and uses `useGLTF.preload()`.
+6. Verify the GLTF/GLB references: buffers, textures, opacity maps, and relative paths.
+
+## Current LOD Models
+
+The current explicit LOD mappings are:
+
+```txt
+ebike
+eolienne
+pylone
+boiteimmeuble
+ecole
+immeuble1
+lafabrik
+maison1
+panneauaffichage
+talkie
+```
+
+## Regression Risks
+
+The most common failure modes are:
+
+- the `*-LOD` folder exists but is missing from `mapLodConfig.ts`
+- a dedicated generated component keeps a hardcoded model path
+- GLTF references point to textures that were renamed during export
+- a model is added to LOD config but does not spawn through `GameMap` or `MapInstancingSystem`
+
+Before committing model changes, validate both the regular and LOD folders for missing GLTF refs.

docs/technical/map-performance.md

@@ -14,12 +14,12 @@ This document tracks the current map-rendering performance pass.
 
 The first performance bottleneck was draw calls. Some assets were exported as many small GLTF primitives even when they used only a few materials.
 
-| Model            | Instances | Meshes / primitives | Notes                                                            |
-| ---------------- | --------: | ------------------: | ---------------------------------------------------------------- |
-| `generateur`     |         3 |                3152 | Worst draw-call offender. Needs asset-side mesh merging.         |
-| `lafabrik`       |         4 |                  56 | Moderate draw calls, heavy 2048 texture set.                     |
-| `ecole`          |         1 |                 107 | One material but many primitives; should be merged.              |
-| `fermeverticale` |         3 |                   1 | Geometry is fine; textures are large for the visible complexity. |
+| Model            | Instances | Meshes / primitives | Notes                                                                                |
+| ---------------- | --------: | ------------------: | ------------------------------------------------------------------------------------ |
+| `generateur`     |         3 |                3152 | Worst draw-call offender. Needs asset-side mesh merging.                             |
+| `lafabrik`       |         4 |                 474 | High primitive count; current HD GLB has embedded geometry and no external textures. |
+| `ecole`          |         1 |                 107 | One material but many primitives; should be merged.                                  |
+| `fermeverticale` |         3 |                   1 | Geometry is fine; textures are large for the visible complexity.                     |
 
 `generateur` was especially expensive because three visible instances could multiply thousands of primitives into thousands of draw calls. Instancing reduces repeated instance cost, but the source asset still needs a cleaner export.
 
@@ -34,7 +34,7 @@ Estimated source primitive count versus runtime merged groups:
 | `generateur` |              3152 |                     8 |
 | `ecole`      |               107 |                     2 |
 | `eolienne`   |               118 |                     8 |
-| `lafabrik`   |                56 |                    14 |
+| `lafabrik`   |               474 |                   ~77 |
 
 This is a code-side safety net, not a replacement for clean asset exports. Clean GLB exports with merged meshes and fewer textures remain the preferred long-term path.
 
@@ -255,7 +255,7 @@ Design/export should prioritize:
 1. Produce lower-poly `buisson`, `arbre`, `sapin`, and crop assets.
 2. Add LOD or billboard variants for far vegetation.
 3. Merge `generateur` meshes from 3152 primitives to a small number of material groups.
-4. Reduce `lafabrik` texture count and downscale flat/low-detail maps.
+4. Keep `lafabrik` exports texture-light, and merge repeated material primitives where possible.
 5. Merge `ecole` primitives because it uses a single material.
 6. Prefer runtime `.glb` or compressed runtime textures when the pipeline supports it.
 

docs/technical/scene-runtime.md

@@ -32,6 +32,8 @@ The loading progress in `HomePage` is monotonic:
 
 This prevents the overlay from jumping backward when nested loaders finish in a slightly different order.
 
+After the initial map boot is complete, late loading signals no longer reopen the full-screen loading overlay. Instead, `HomePage` shows the compact `AppLoadingIndicator` while the game remains visible. This is reserved for explicit runtime reload signals such as graphics preset changes, repair-state transitions, or late world loading events; chunk streaming intentionally does not drive this indicator.
+
 ## World Composition
 
 `src/world/World.tsx` is the main scene composer.