feat(repair): broken parts spawn from exploded model node positions

Render the exploded mission model during the repairing step so broken
nodes (e.g. ebike refroidisseur) stay visible in the world, and surface
their world positions to RepairRepairingStep so broken pieces spawn
from where they belong on the model rather than from a static offset.

- ExplodableModel: add hideNodeNames (mesh visibility off, restored on
  unmount) and nodeAnchorNames + onNodeAnchorsChange (per-frame world
  positions debounced via signature so React state updates only when
  the values actually move).
- RepairGame: render ExplodableModel during 'repairing' with the broken
  node names hidden + anchors forwarded; threads brokenAnchors state
  to RepairRepairingStep.
- RepairScanSequence + RepairRepairingStep: propagate targetNodeName
  through scanned and fallback broken-part lists.
- RepairRepairingStep: broken parts spawn at brokenAnchors[targetNodeName]
  when set, falling back to legacy BROKEN_PART_START_OFFSETS otherwise.

src/components/three/gameplay/RepairGame.tsx

@@ -1,6 +1,7 @@
 import { Suspense, useEffect, useMemo, useState } from "react";
 import { useGLTF } from "@react-three/drei";
 import { ExplodableModel } from "@/components/three/models/ExplodableModel";
+import type { ExplodedNodeAnchors } from "@/components/three/models/ExplodableModel";
 import type {
   RepairCasePartAnchors,
   RepairCasePlaceholder,
@@ -67,12 +68,14 @@ export function RepairGame({
     readonly RepairCasePlaceholder[]
   >([]);
   const [caseAnchors, setCaseAnchors] = useState<RepairCasePartAnchors>({});
+  const [brokenAnchors, setBrokenAnchors] = useState<ExplodedNodeAnchors>({});
   const [scannedBrokenParts, setScannedBrokenParts] = useState<
     readonly RepairScannedBrokenPart[]
   >([]);
   const parsedScale = toVector3Scale(scale);
   const snappedPosition = useTerrainSnappedPosition(position);
   const readyForFragmentation = step === "inspected";
+  const brokenNodeNames = useMemo(() => getBrokenNodeNames(config), [config]);
 
   useRepairFragmentationInput({
     enabled: mainState === mission && readyForFragmentation,
@@ -86,6 +89,7 @@ export function RepairGame({
     const timeoutId = window.setTimeout(() => {
       setCasePlaceholders([]);
       setCaseAnchors({});
+      setBrokenAnchors({});
       setScannedBrokenParts([]);
     }, 0);
 
@@ -141,13 +145,24 @@ export function RepairGame({
           />
         ) : null}
         {step === "repairing" ? (
-          <RepairRepairingStep
-            anchors={caseAnchors}
-            brokenParts={scannedBrokenParts}
-            config={config}
-            placeholders={casePlaceholders}
-            onRepair={() => setMissionStep(mission, "reassembling")}
-          />
+          <>
+            <ExplodableModel
+              modelPath={config.modelPath}
+              scale={config.modelScale ?? 1}
+              split
+              hideNodeNames={brokenNodeNames}
+              nodeAnchorNames={brokenNodeNames}
+              onNodeAnchorsChange={setBrokenAnchors}
+            />
+            <RepairRepairingStep
+              anchors={caseAnchors}
+              brokenAnchors={brokenAnchors}
+              brokenParts={scannedBrokenParts}
+              config={config}
+              placeholders={casePlaceholders}
+              onRepair={() => setMissionStep(mission, "reassembling")}
+            />
+          </>
         ) : null}
         {step === "reassembling" ? (
           <RepairReassemblyStep
@@ -195,3 +210,15 @@ function getRepairMissionModelPaths(config: RepairMissionConfig): string[] {
     ]),
   ];
 }
+
+function getBrokenNodeNames(config: RepairMissionConfig): readonly string[] {
+  const names = new Set<string>();
+  config.brokenParts.forEach((part) => {
+    if (part.targetNodeName) names.add(part.targetNodeName);
+    else if (part.nodeName) names.add(part.nodeName);
+  });
+  config.replacementParts.forEach((part) => {
+    if (part.targetNodeName) names.add(part.targetNodeName);
+  });
+  return Array.from(names);
+}

src/components/three/gameplay/RepairRepairingStep.tsx

@@ -4,6 +4,7 @@ import type {
   RepairCasePartAnchors,
   RepairCasePlaceholder,
 } from "@/components/three/gameplay/RepairCaseModel";
+import type { ExplodedNodeAnchors } from "@/components/three/models/ExplodableModel";
 import { RepairObjectModel } from "@/components/three/gameplay/RepairObjectModel";
 import { RepairPromptVideo } from "@/components/three/gameplay/RepairPromptVideo";
 import { GrabbableObject } from "@/components/three/interaction/GrabbableObject";
@@ -42,6 +43,7 @@ let hasWarnedMissingPlaceholders = false;
 
 interface RepairRepairingStepProps {
   anchors?: RepairCasePartAnchors;
+  brokenAnchors?: ExplodedNodeAnchors;
   brokenParts: readonly RepairScannedBrokenPart[];
   config: RepairMissionConfig;
   placeholders: readonly RepairCasePlaceholder[];
@@ -68,6 +70,7 @@ interface RepairPartPlacementFeedbackProps {
 
 export function RepairRepairingStep({
   anchors = {},
+  brokenAnchors = {},
   brokenParts,
   config,
   placeholders,
@@ -272,14 +275,18 @@ export function RepairRepairingStep({
       })}
 
       {brokenPartsToDeposit.map((part, index) => {
-        const startOffset =
+        const fallbackOffset =
           BROKEN_PART_START_OFFSETS[index % BROKEN_PART_START_OFFSETS.length] ??
           BROKEN_PART_START_OFFSETS[0]!;
-        const startPosition: Vector3Tuple = [
-          REPAIR_CASE_FOCUS_POSITION[0] + startOffset[0],
-          REPAIR_CASE_FOCUS_POSITION[1] + startOffset[1],
-          REPAIR_CASE_FOCUS_POSITION[2] + startOffset[2],
+        const fallbackPosition: Vector3Tuple = [
+          REPAIR_CASE_FOCUS_POSITION[0] + fallbackOffset[0],
+          REPAIR_CASE_FOCUS_POSITION[1] + fallbackOffset[1],
+          REPAIR_CASE_FOCUS_POSITION[2] + fallbackOffset[2],
         ];
+        const anchorPosition = part.targetNodeName
+          ? brokenAnchors[part.targetNodeName]
+          : undefined;
+        const startPosition: Vector3Tuple = anchorPosition ?? fallbackPosition;
         const targetPositions = getBrokenPartTargetPositions(
           part,
           placeholderTargets,
@@ -529,5 +536,6 @@ function getBrokenPartsToDeposit(
     label: part.label,
     modelPath: part.modelPath ?? config.modelPath,
     ...(part.caseSlotName ? { caseSlotName: part.caseSlotName } : {}),
+    ...(part.targetNodeName ? { targetNodeName: part.targetNodeName } : {}),
   }));
 }

src/components/three/gameplay/RepairScanSequence.tsx

@@ -97,6 +97,9 @@ function getScannedBrokenParts(
       ...(match.config.caseSlotName
         ? { caseSlotName: match.config.caseSlotName }
         : {}),
+      ...(match.config.targetNodeName
+        ? { targetNodeName: match.config.targetNodeName }
+        : {}),
     };
   });
 }

src/components/three/models/ExplodableModel.tsx

@@ -1,5 +1,6 @@
 import type { ReactNode } from "react";
-import { Component, useEffect, useMemo } from "react";
+import { Component, useEffect, useMemo, useRef } from "react";
+import * as THREE from "three";
 import { useFrame } from "@react-three/fiber";
 import { useLoggedGLTF } from "@/hooks/three/useLoggedGLTF";
 import { useClonedObject } from "@/hooks/three/useClonedObject";
@@ -9,6 +10,10 @@ import type { ModelTransformProps, Vector3Tuple } from "@/types/three/three";
 import { logModelLoadError } from "@/utils/three/modelLoadLogger";
 import { toVector3Scale } from "@/utils/three/scale";
 
+export type ExplodedNodeAnchors = Readonly<Record<string, Vector3Tuple>>;
+
+const _anchorWorld = new THREE.Vector3();
+
 interface ModelErrorBoundaryProps {
   children: ReactNode;
   modelPath: string;
@@ -67,6 +72,9 @@ interface ExplodableModelInnerProps extends ModelTransformProps {
   split: boolean;
   splitDistance?: number;
   onPartsReady?: (parts: readonly ExplodedPart[]) => void;
+  hideNodeNames?: readonly string[];
+  nodeAnchorNames?: readonly string[];
+  onNodeAnchorsChange?: (anchors: ExplodedNodeAnchors) => void;
 }
 
 export function ExplodableModel(
@@ -93,6 +101,9 @@ function ExplodableModelInner({
   scale = 1,
   splitDistance = 1.2,
   onPartsReady,
+  hideNodeNames,
+  nodeAnchorNames,
+  onNodeAnchorsChange,
 }: ExplodableModelInnerProps): React.JSX.Element {
   const { scene } = useLoggedGLTF(modelPath, {
     scope: "ExplodableModel",
@@ -106,6 +117,24 @@ function ExplodableModelInner({
     [model, splitDistance],
   );
   const parsedScale = toVector3Scale(scale);
+  const anchorSignatureRef = useRef("");
+
+  useEffect(() => {
+    if (!hideNodeNames || hideNodeNames.length === 0) return;
+    const hidden: THREE.Object3D[] = [];
+    model.traverse((child) => {
+      if (hideNodeNames.includes(child.name)) {
+        hidden.push(child);
+        child.visible = false;
+      }
+    });
+
+    return () => {
+      hidden.forEach((object) => {
+        object.visible = true;
+      });
+    };
+  }, [hideNodeNames, model]);
 
   useEffect(() => {
     explodedModel.setSplit(split);
@@ -117,6 +146,35 @@ function ExplodableModelInner({
 
   useFrame((_, delta) => {
     explodedModel.update(delta);
+
+    if (
+      !onNodeAnchorsChange ||
+      !nodeAnchorNames ||
+      nodeAnchorNames.length === 0
+    ) {
+      return;
+    }
+
+    const anchors: Record<string, Vector3Tuple> = {};
+    nodeAnchorNames.forEach((name) => {
+      const node = model.getObjectByName(name);
+      if (!node) return;
+      node.getWorldPosition(_anchorWorld);
+      anchors[name] = [_anchorWorld.x, _anchorWorld.y, _anchorWorld.z];
+    });
+
+    const signature = nodeAnchorNames
+      .map((name) => {
+        const a = anchors[name];
+        return a
+          ? `${name}:${a[0].toFixed(3)},${a[1].toFixed(3)},${a[2].toFixed(3)}`
+          : `${name}:?`;
+      })
+      .join("|");
+
+    if (signature === anchorSignatureRef.current) return;
+    anchorSignatureRef.current = signature;
+    onNodeAnchorsChange(anchors);
   });
 
   return (