diff --git a/cmake/targets/psp.cmake b/cmake/targets/psp.cmake
index 32a2b5a5..42d4cfcb 100644
--- a/cmake/targets/psp.cmake
+++ b/cmake/targets/psp.cmake
@@ -55,7 +55,6 @@ target_compile_definitions(${DUSK_BINARY_TARGET_NAME} PUBLIC
   DUSK_DISPLAY_WIDTH=480
   DUSK_DISPLAY_HEIGHT=272
   DUSK_THREAD_PTHREAD
-  DUSK_TIME_DYNAMIC
   DUSK_DISPLAY_OVERSCAN=6
 )
 
diff --git a/src/dusk/engine/engine.c b/src/dusk/engine/engine.c
index 567c7d03..9052d5e5 100644
--- a/src/dusk/engine/engine.c
+++ b/src/dusk/engine/engine.c
@@ -72,6 +72,10 @@ errorret_t engineInit(const int32_t argc, const char_t **argv) {
   entityAddComponent(
     testEntities, ENGINE.testCubeEntity, COMPONENT_TYPE_RENDERABLE
   );
+  entityUpdateAdd(
+    testEntities, ENGINE.testCubeEntity, engineTestCubeRotate,
+    ENGINE.testCubePositionComponent, NULL
+  );
 
   networkRequestConnection(
     engineNetworkOnConnected,
@@ -111,15 +115,6 @@ errorret_t engineUpdate(void) {
     inputUpdate();
     consoleUpdate();
 
-    // Test: spin the cube.
-    ENGINE.testCubeRotation += TIME.delta;
-    entityPositionSetLocalRotation(
-      sceneGetEntities(ENGINE.testSceneId),
-      ENGINE.testCubeEntity,
-      ENGINE.testCubePositionComponent,
-      (vec3){ 0.0f, ENGINE.testCubeRotation, 0.0f }
-    );
-
     errorChain(sceneUpdate());
     errorChain(assetUpdate());
     errorChain(uiUpdate());
@@ -212,3 +207,16 @@ void engineNetworkOnDisconnect(errorret_t error, void *user) {
 void engineNetworkDisconnectTestOnComplete(void *user) {
   consolePrint("Network disconnect test complete");
 }
+
+void engineTestCubeRotate(
+  entitymanager_t *mgr,
+  const entityid_t entityId,
+  const componentid_t componentId,
+  void *user
+) {
+  ENGINE.testCubeRotation += TIME.delta;
+  entityPositionSetLocalRotation(
+    mgr, entityId, componentId,
+    (vec3){ 0.0f, ENGINE.testCubeRotation, 0.0f }
+  );
+}
diff --git a/src/dusk/engine/engine.h b/src/dusk/engine/engine.h
index 369d31cb..3e4b0c38 100644
--- a/src/dusk/engine/engine.h
+++ b/src/dusk/engine/engine.h
@@ -98,3 +98,21 @@ void engineNetworkOnDisconnect(errorret_t error, void *user);
  * @param user Unused.
  */
 void engineNetworkDisconnectTestOnComplete(void *user);
+
+/**
+ * Entity update callback that spins the test cube around Y. Registered
+ * once in engineInit() via entityUpdateAdd(), so it only runs from
+ * sceneFixedUpdate() -- once per fixed timestep, never once per rendered
+ * frame.
+ *
+ * @param mgr The entity manager that owns the entity.
+ * @param entityId The test cube's entity ID.
+ * @param componentId The test cube's position component ID.
+ * @param user Unused.
+ */
+void engineTestCubeRotate(
+  entitymanager_t *mgr,
+  const entityid_t entityId,
+  const componentid_t componentId,
+  void *user
+);
diff --git a/src/dusk/entity/entity.c b/src/dusk/entity/entity.c
index 392a5e3d..70026036 100644
--- a/src/dusk/entity/entity.c
+++ b/src/dusk/entity/entity.c
@@ -86,7 +86,9 @@ void entityDisposeDeep(entitymanager_t *mgr, const entityid_t entityId) {
 void entityUpdate(entitymanager_t *mgr, const entityid_t entityId) {
   entity_t *ent = &mgr->entities[entityId];
   for(uint8_t i = 0; i < ent->updateCount; i++) {
-    ent->onUpdate[i](entityId, ent->updateComponentId[i], ent->updateUser[i]);
+    ent->onUpdate[i](
+      mgr, entityId, ent->updateComponentId[i], ent->updateUser[i]
+    );
   }
 }
 
@@ -96,7 +98,7 @@ void entityDispose(entitymanager_t *mgr, const entityid_t entityId) {
 
   for(uint8_t i = 0; i < ent->disposeCount; i++) {
     ent->onDispose[i](
-      entityId, ent->disposeComponentId[i], ent->disposeUser[i]
+      mgr, entityId, ent->disposeComponentId[i], ent->disposeUser[i]
     );
   }
 
diff --git a/src/dusk/entity/entity.h b/src/dusk/entity/entity.h
index a1b02f82..b67a441c 100644
--- a/src/dusk/entity/entity.h
+++ b/src/dusk/entity/entity.h
@@ -14,6 +14,7 @@
 #define ENTITY_DISPOSE_CALLBACK_COUNT_MAX 5
 
 typedef void (*entitycallback_t)(
+  entitymanager_t *mgr,
   const entityid_t entityId,
   const componentid_t componentId,
   void *user
diff --git a/src/dusk/physics/CMakeLists.txt b/src/dusk/physics/CMakeLists.txt
index 3eeca058..1de6a434 100644
--- a/src/dusk/physics/CMakeLists.txt
+++ b/src/dusk/physics/CMakeLists.txt
@@ -8,4 +8,5 @@ target_sources(${DUSK_LIBRARY_TARGET_NAME}
   PUBLIC
     physicsworld.c
     physicstest.c
+    physicsshapemesh.c
 )
diff --git a/src/dusk/physics/physicsshapemesh.c b/src/dusk/physics/physicsshapemesh.c
new file mode 100644
index 00000000..e91c05dd
--- /dev/null
+++ b/src/dusk/physics/physicsshapemesh.c
@@ -0,0 +1,151 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "physicsshapemesh.h"
+#include "physicstest.h"
+#include "assert/assert.h"
+
+void physicsShapeMeshGetVertex(
+  const physicsshapemesh_t *mesh, const uint32_t index, vec3 out
+) {
+  assertNotNull(mesh, "Mesh cannot be null");
+  assertTrue(index < mesh->triangleCount * 3, "Vertex index OOB");
+
+  const float_t *p = (const float_t *)(mesh->vertices + (size_t)index * mesh->stride);
+  out[0] = p[0];
+  out[1] = p[1];
+  out[2] = p[2];
+}
+
+bool_t physicsShapeMeshTestSphere(
+  const physicsshapemesh_t *mesh, const vec3 meshPos,
+  const vec3 sphereCenter, const float_t sphereRadius,
+  vec3 outNormal, float_t *outDepth
+) {
+  assertNotNull(mesh, "Mesh cannot be null");
+
+  bool_t found = false;
+  float_t bestDist2 = 0.0f;
+  vec3 bestPoint;
+
+  for(uint32_t i = 0; i < mesh->triangleCount; i++) {
+    vec3 a, b, c;
+    physicsShapeMeshGetVertex(mesh, i * 3 + 0, a);
+    physicsShapeMeshGetVertex(mesh, i * 3 + 1, b);
+    physicsShapeMeshGetVertex(mesh, i * 3 + 2, c);
+    glm_vec3_add(a, (float_t *)meshPos, a);
+    glm_vec3_add(b, (float_t *)meshPos, b);
+    glm_vec3_add(c, (float_t *)meshPos, c);
+
+    vec3 closest;
+    physicsTestClosestPointOnTriangle(sphereCenter, a, b, c, closest);
+
+    vec3 diff;
+    glm_vec3_sub((float_t *)sphereCenter, closest, diff);
+    float_t dist2 = glm_vec3_norm2(diff);
+    if(found && dist2 >= bestDist2) continue;
+
+    found = true;
+    bestDist2 = dist2;
+    glm_vec3_copy(closest, bestPoint);
+  }
+
+  if(!found || bestDist2 >= sphereRadius * sphereRadius) return false;
+
+  float_t dist = sqrtf(bestDist2);
+  *outDepth = sphereRadius - dist;
+
+  vec3 diff;
+  glm_vec3_sub((float_t *)sphereCenter, bestPoint, diff);
+  if(dist > 1e-6f) {
+    glm_vec3_scale(diff, 1.0f / dist, outNormal);
+  } else {
+    outNormal[0] = 0.0f;
+    outNormal[1] = 1.0f;
+    outNormal[2] = 0.0f;
+  }
+  return true;
+}
+
+bool_t physicsShapeMeshTestCapsule(
+  const physicsshapemesh_t *mesh, const vec3 meshPos,
+  const vec3 capsuleCenter, const float_t capsuleRadius,
+  const float_t capsuleHalfHeight,
+  vec3 outNormal, float_t *outDepth
+) {
+  vec3 capA = {
+    capsuleCenter[0], capsuleCenter[1] - capsuleHalfHeight, capsuleCenter[2]
+  };
+  vec3 capB = {
+    capsuleCenter[0], capsuleCenter[1] + capsuleHalfHeight, capsuleCenter[2]
+  };
+
+  int32_t sampleCount = capsuleRadius > 1e-6f
+    ? (int32_t)ceilf((2.0f * capsuleHalfHeight) / capsuleRadius) + 1
+    : 2;
+  if(sampleCount < 2) sampleCount = 2;
+  if(sampleCount > PHYSICS_SHAPE_MESH_CAPSULE_SAMPLES_MAX) {
+    sampleCount = PHYSICS_SHAPE_MESH_CAPSULE_SAMPLES_MAX;
+  }
+
+  bool_t found = false;
+  vec3 bestNormal = { 0.0f, 1.0f, 0.0f };
+  float_t bestDepth = 0.0f;
+
+  for(int32_t i = 0; i < sampleCount; i++) {
+    float_t t = (float_t)i / (float_t)(sampleCount - 1);
+    vec3 samplePoint;
+    glm_vec3_lerp(capA, capB, t, samplePoint);
+
+    vec3 normal; float_t depth;
+    if(!physicsShapeMeshTestSphere(
+      mesh, meshPos, samplePoint, capsuleRadius, normal, &depth
+    )) continue;
+
+    if(found && depth <= bestDepth) continue;
+    found = true;
+    bestDepth = depth;
+    glm_vec3_copy(normal, bestNormal);
+  }
+
+  if(!found) return false;
+  *outDepth = bestDepth;
+  glm_vec3_copy(bestNormal, outNormal);
+  return true;
+}
+
+bool_t physicsShapeMeshTest(
+  const vec3 selfPos, const void *selfData,
+  const vec3 otherPos, const physicsshape_t *otherShape,
+  vec3 outNormal, float_t *outDepth
+) {
+  const physicsshapemesh_t *mesh = (const physicsshapemesh_t *)selfData;
+
+  switch(otherShape->type) {
+    case PHYSICS_SHAPE_SPHERE:
+      return physicsShapeMeshTestSphere(
+        mesh, selfPos, otherPos, otherShape->data.sphere.radius,
+        outNormal, outDepth
+      );
+    case PHYSICS_SHAPE_CAPSULE:
+      return physicsShapeMeshTestCapsule(
+        mesh, selfPos, otherPos,
+        otherShape->data.capsule.radius, otherShape->data.capsule.halfHeight,
+        outNormal, outDepth
+      );
+    default:
+      return false;
+  }
+}
+
+physicsshape_t physicsShapeMeshCreate(const physicsshapemesh_t *mesh) {
+  assertNotNull(mesh, "Mesh cannot be null");
+  return (physicsshape_t){
+    .type = PHYSICS_SHAPE_CUSTOM,
+    .data.custom = { .userData = (void *)mesh, .test = physicsShapeMeshTest }
+  };
+}
diff --git a/src/dusk/physics/physicsshapemesh.h b/src/dusk/physics/physicsshapemesh.h
new file mode 100644
index 00000000..37f882bc
--- /dev/null
+++ b/src/dusk/physics/physicsshapemesh.h
@@ -0,0 +1,128 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "physicsshape.h"
+
+/**
+ * Capsule-vs-mesh is approximated by sampling spheres along the capsule's
+ * axis (see physicsShapeMeshTestCapsule). This bounds how many samples a
+ * single query can take, regardless of how tall/thin the capsule is.
+ */
+#define PHYSICS_SHAPE_MESH_CAPSULE_SAMPLES_MAX 8
+
+/**
+ * Describes an arbitrary triangle mesh (e.g. landscape/terrain geometry)
+ * for use as a PHYSICS_SHAPE_CUSTOM shape via physicsShapeMeshCreate().
+ *
+ * Vertex positions are read directly out of `vertices` at `stride`-byte
+ * intervals, so this can point straight at an existing render vertex
+ * buffer (e.g. `&myMeshVertices[0].pos` with `stride = sizeof(meshvertex_t)`)
+ * with no need to duplicate the geometry for physics -- as long as each
+ * vertex's position is 3 consecutive float_t.
+ *
+ * Not copied or owned: this struct (and the buffer it points into) must
+ * outlive any physicsshape_t built from it, so it's typically a field
+ * alongside whatever owns the mesh (e.g. a terrain chunk).
+ *
+ * Every query scans all triangleCount triangles (no broad-phase/BVH), so
+ * for good performance keep each mesh shape scoped to one reasonably-sized
+ * chunk rather than an entire world, and only add nearby chunks' physics
+ * bodies to the scene.
+ */
+typedef struct {
+  /** Pointer to the first triangle vertex's position (3 consecutive float_t). */
+  const uint8_t *vertices;
+  /** Byte stride between consecutive vertex positions. */
+  size_t stride;
+  /** Number of triangles. `vertices` holds triangleCount * 3 positions. */
+  uint32_t triangleCount;
+} physicsshapemesh_t;
+
+/**
+ * Reads the world-space position of a single mesh vertex (vertex index,
+ * not triangle index -- pass triangleIndex * 3 + 0/1/2 for a triangle's
+ * corners).
+ *
+ * @param mesh The mesh to read from.
+ * @param index Vertex index, in [0, triangleCount * 3).
+ * @param out Receives the vertex position.
+ */
+void physicsShapeMeshGetVertex(
+  const physicsshapemesh_t *mesh, const uint32_t index, vec3 out
+);
+
+/**
+ * Tests a sphere against every triangle in the mesh, keeping only the
+ * single closest triangle. outNormal points from the mesh surface toward
+ * the sphere (self toward other, per physicsshapecustomtest_t).
+ *
+ * @param mesh The mesh to test against.
+ * @param meshPos World-space position of the mesh shape's owning entity;
+ * added to every vertex read from mesh.
+ * @param sphereCenter World-space center of the sphere.
+ * @param sphereRadius Radius of the sphere.
+ * @param outNormal Push-out normal (mesh surface toward sphere).
+ * @param outDepth Penetration depth.
+ * @return true if the sphere overlaps the mesh.
+ */
+bool_t physicsShapeMeshTestSphere(
+  const physicsshapemesh_t *mesh, const vec3 meshPos,
+  const vec3 sphereCenter, const float_t sphereRadius,
+  vec3 outNormal, float_t *outDepth
+);
+
+/**
+ * Tests a Y-axis-aligned capsule against the mesh by approximating the
+ * capsule as a series of spheres sampled along its axis (see
+ * PHYSICS_SHAPE_MESH_CAPSULE_SAMPLES_MAX) and keeping the deepest overlap
+ * found. An approximation, not an exact capsule-vs-triangle test.
+ *
+ * @param mesh The mesh to test against.
+ * @param meshPos World-space position of the mesh shape's owning entity.
+ * @param capsuleCenter World-space center of the capsule.
+ * @param capsuleRadius Radius of the capsule.
+ * @param capsuleHalfHeight Half-height of the capsule's cylindrical segment.
+ * @param outNormal Push-out normal (mesh surface toward capsule).
+ * @param outDepth Penetration depth.
+ * @return true if the capsule overlaps the mesh.
+ */
+bool_t physicsShapeMeshTestCapsule(
+  const physicsshapemesh_t *mesh, const vec3 meshPos,
+  const vec3 capsuleCenter, const float_t capsuleRadius,
+  const float_t capsuleHalfHeight,
+  vec3 outNormal, float_t *outDepth
+);
+
+/**
+ * physicsshapecustomtest_t implementation backing physicsShapeMeshCreate().
+ * Routes to physicsShapeMeshTestSphere/TestCapsule depending on
+ * otherShape's type. Cube (AABB) bodies are not supported yet and never
+ * collide against a mesh shape.
+ *
+ * @param selfPos The mesh shape's position.
+ * @param selfData The physicsshapemesh_t this shape was created from.
+ * @param otherPos The other shape's position.
+ * @param otherShape The other shape's descriptor.
+ * @param outNormal Push-out normal (mesh surface toward other).
+ * @param outDepth Penetration depth.
+ * @return true if the shapes overlap.
+ */
+bool_t physicsShapeMeshTest(
+  const vec3 selfPos, const void *selfData,
+  const vec3 otherPos, const physicsshape_t *otherShape,
+  vec3 outNormal, float_t *outDepth
+);
+
+/**
+ * Builds a PHYSICS_SHAPE_CUSTOM shape backed by the given triangle mesh.
+ *
+ * @param mesh Mesh descriptor. Must outlive the returned shape (see
+ * physicsshapemesh_t).
+ * @return A physicsshape_t wired to test against this mesh.
+ */
+physicsshape_t physicsShapeMeshCreate(const physicsshapemesh_t *mesh);
diff --git a/src/dusk/physics/physicstest.c b/src/dusk/physics/physicstest.c
index 714f03e0..8ab29307 100644
--- a/src/dusk/physics/physicstest.c
+++ b/src/dusk/physics/physicstest.c
@@ -148,6 +148,78 @@ void physicsTestClosestPointOnSegment(
   glm_vec3_lerp((float_t *)a, (float_t *)b, t, out);
 }
 
+void physicsTestClosestPointOnTriangle(
+  const vec3 p, const vec3 a, const vec3 b, const vec3 c, vec3 out
+) {
+  vec3 ab, ac, ap;
+  glm_vec3_sub((float_t *)b, (float_t *)a, ab);
+  glm_vec3_sub((float_t *)c, (float_t *)a, ac);
+  glm_vec3_sub((float_t *)p, (float_t *)a, ap);
+
+  float_t d1 = glm_vec3_dot(ab, ap);
+  float_t d2 = glm_vec3_dot(ac, ap);
+  if(d1 <= 0.0f && d2 <= 0.0f) {
+    glm_vec3_copy((float_t *)a, out);
+    return;
+  }
+
+  vec3 bp;
+  glm_vec3_sub((float_t *)p, (float_t *)b, bp);
+  float_t d3 = glm_vec3_dot(ab, bp);
+  float_t d4 = glm_vec3_dot(ac, bp);
+  if(d3 >= 0.0f && d4 <= d3) {
+    glm_vec3_copy((float_t *)b, out);
+    return;
+  }
+
+  float_t vc = d1 * d4 - d3 * d2;
+  if(vc <= 0.0f && d1 >= 0.0f && d3 <= 0.0f) {
+    float_t v = d1 / (d1 - d3);
+    vec3 scaled;
+    glm_vec3_scale(ab, v, scaled);
+    glm_vec3_add((float_t *)a, scaled, out);
+    return;
+  }
+
+  vec3 cp;
+  glm_vec3_sub((float_t *)p, (float_t *)c, cp);
+  float_t d5 = glm_vec3_dot(ab, cp);
+  float_t d6 = glm_vec3_dot(ac, cp);
+  if(d6 >= 0.0f && d5 <= d6) {
+    glm_vec3_copy((float_t *)c, out);
+    return;
+  }
+
+  float_t vb = d5 * d2 - d1 * d6;
+  if(vb <= 0.0f && d2 >= 0.0f && d6 <= 0.0f) {
+    float_t w = d2 / (d2 - d6);
+    vec3 scaled;
+    glm_vec3_scale(ac, w, scaled);
+    glm_vec3_add((float_t *)a, scaled, out);
+    return;
+  }
+
+  float_t va = d3 * d6 - d5 * d4;
+  if(va <= 0.0f && (d4 - d3) >= 0.0f && (d5 - d6) >= 0.0f) {
+    float_t w = (d4 - d3) / ((d4 - d3) + (d5 - d6));
+    vec3 bc, scaled;
+    glm_vec3_sub((float_t *)c, (float_t *)b, bc);
+    glm_vec3_scale(bc, w, scaled);
+    glm_vec3_add((float_t *)b, scaled, out);
+    return;
+  }
+
+  // Interior: barycentric combination of ab and ac from a.
+  float_t denom = 1.0f / (va + vb + vc);
+  float_t v = vb * denom;
+  float_t w = vc * denom;
+  vec3 abScaled, acScaled, sum;
+  glm_vec3_scale(ab, v, abScaled);
+  glm_vec3_scale(ac, w, acScaled);
+  glm_vec3_add(abScaled, acScaled, sum);
+  glm_vec3_add((float_t *)a, sum, out);
+}
+
 void physicsTestClosestPointsBetweenSegments(
   const vec3 a1, const vec3 b1,
   const vec3 a2, const vec3 b2,
diff --git a/src/dusk/physics/physicstest.h b/src/dusk/physics/physicstest.h
index debb5860..3cca1772 100644
--- a/src/dusk/physics/physicstest.h
+++ b/src/dusk/physics/physicstest.h
@@ -110,6 +110,21 @@ void physicsTestClosestPointOnSegment(
   const vec3 a, const vec3 b, const vec3 p, vec3 out
 );
 
+/**
+ * Finds the closest point on triangle (a, b, c) to query point p. Handles
+ * all six Voronoi regions (the three vertices, the three edges, and the
+ * face interior).
+ *
+ * @param p    Query point.
+ * @param a    First triangle vertex.
+ * @param b    Second triangle vertex.
+ * @param c    Third triangle vertex.
+ * @param out  Receives the closest point on the triangle to p.
+ */
+void physicsTestClosestPointOnTriangle(
+  const vec3 p, const vec3 a, const vec3 b, const vec3 c, vec3 out
+);
+
 /**
  * Finds the closest points between two line segments.
  *
diff --git a/src/dusk/scene/scene.c b/src/dusk/scene/scene.c
index 29703880..86deabc1 100644
--- a/src/dusk/scene/scene.c
+++ b/src/dusk/scene/scene.c
@@ -72,12 +72,17 @@ physicsworld_t *sceneGetPhysics(const sceneid_t id) {
 }
 
 errorret_t sceneUpdate(void) {
-  if(SCENE_MANAGER.active == SCENE_ID_INVALID) errorOk();
-
   #if DUSK_TIME_DYNAMIC
-    if(!TIME.dynamicUpdate) errorOk();
+    if(TIME.dynamicUpdate) errorOk();
   #endif
 
+  errorChain(sceneFixedUpdate());
+  errorOk();
+}
+
+errorret_t sceneFixedUpdate(void) {
+  if(SCENE_MANAGER.active == SCENE_ID_INVALID) errorOk();
+
   scene_t *scene = &SCENE_MANAGER.scenes[SCENE_MANAGER.active];
   entityManagerUpdate(&scene->entities);
   physicsWorldStep(&scene->physics, &scene->entities, TIME.delta);
diff --git a/src/dusk/scene/scene.h b/src/dusk/scene/scene.h
index 6762903b..fafdf910 100644
--- a/src/dusk/scene/scene.h
+++ b/src/dusk/scene/scene.h
@@ -83,13 +83,29 @@ entitymanager_t *sceneGetEntities(const sceneid_t id);
 physicsworld_t *sceneGetPhysics(const sceneid_t id);
 
 /**
- * Ticks the active scene's entities (update callbacks, then a physics
- * step) on fixed timesteps only, per DUSK_TIME_DYNAMIC.
+ * Called every frame (every call to engineUpdate). On a non-dynamic-time
+ * platform (DUSK_TIME_DYNAMIC undefined) every frame is itself a fixed
+ * timestep, so this calls sceneFixedUpdate() every time. On a
+ * dynamic-time platform, most calls are sub-steps still accumulating
+ * toward the next fixed timestep (TIME.dynamicUpdate is true) and do
+ * nothing here; this calls sceneFixedUpdate() only on the one call where
+ * TIME.dynamicUpdate is false, i.e. exactly once per fixed timestep.
  *
  * @return An error if the update failed, or errorOk() if it succeeded.
  */
 errorret_t sceneUpdate(void);
 
+/**
+ * Ticks the active scene's entities (update callbacks, then a physics
+ * step) by one fixed timestep (TIME.delta). Called by sceneUpdate() at
+ * the fixed-timestep cadence described there -- never once per rendered
+ * frame on a dynamic-time platform, so game logic and physics stay
+ * frame-rate independent and deterministic.
+ *
+ * @return An error if the update failed, or errorOk() if it succeeded.
+ */
+errorret_t sceneFixedUpdate(void);
+
 /**
  * Renders the active scene (entities, render pipeline, UI).
  *
diff --git a/src/dusk/time/time.h b/src/dusk/time/time.h
index 68f53537..52b14c8e 100644
--- a/src/dusk/time/time.h
+++ b/src/dusk/time/time.h
@@ -39,13 +39,26 @@
 #endif
 
 typedef struct {
+  /** Fixed simulation timestep, always DUSK_TIME_STEP. */
   float_t delta;
+  /** Total elapsed fixed-simulation time, in DUSK_TIME_STEP increments. */
   float_t time;
 
   #ifdef DUSK_TIME_DYNAMIC
+    /** dynamicTime at the last fixed-timestep boundary. */
     float_t lastNonDynamic;
+    /**
+     * False on the one timeUpdate() call per fixed timestep where enough
+     * real time has accumulated to cross a DUSK_TIME_STEP boundary (delta
+     * and time were just advanced) -- true on every other call, still
+     * accumulating toward the next one. Fixed-rate systems (scene
+     * fixed update, physics) should run only when this is false; systems
+     * that want every real frame (e.g. rendering) run unconditionally.
+     */
     bool_t dynamicUpdate;
+    /** Real elapsed time since the previous timeUpdate() call. */
     float_t dynamicDelta;
+    /** Total elapsed real time, accumulated every timeUpdate() call. */
     float_t dynamicTime;
   #endif
 } dusktime_t;
diff --git a/test/physics/CMakeLists.txt b/test/physics/CMakeLists.txt
index 99e90c07..6e9f6a0a 100644
--- a/test/physics/CMakeLists.txt
+++ b/test/physics/CMakeLists.txt
@@ -8,3 +8,4 @@ include(dusktest)
 # Tests
 dusktest(test_physicstest.c)
 dusktest(test_physicsworld.c)
+dusktest(test_physicsshapemesh.c)
diff --git a/test/physics/test_physicsshapemesh.c b/test/physics/test_physicsshapemesh.c
new file mode 100644
index 00000000..a136ae9e
--- /dev/null
+++ b/test/physics/test_physicsshapemesh.c
@@ -0,0 +1,185 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "dusktest.h"
+#include "util/memory.h"
+#include "physics/physicstest.h"
+#include "physics/physicsshapemesh.h"
+
+// A flat 10x10 ground quad on the XZ plane at y=0, centered at the origin
+// (two triangles, tightly packed vec3 vertices -- no indices).
+static vec3 FLAT_GROUND_VERTICES[6] = {
+  { -5.0f, 0.0f, -5.0f }, {  5.0f, 0.0f, -5.0f }, {  5.0f, 0.0f,  5.0f },
+  { -5.0f, 0.0f, -5.0f }, {  5.0f, 0.0f,  5.0f }, { -5.0f, 0.0f,  5.0f },
+};
+
+static physicsshapemesh_t flatGroundMesh(void) {
+  return (physicsshapemesh_t){
+    .vertices = (const uint8_t *)FLAT_GROUND_VERTICES,
+    .stride = sizeof(vec3),
+    .triangleCount = 2
+  };
+}
+
+static void test_getVertexReadsRawPositions(void **state) {
+  physicsshapemesh_t mesh = flatGroundMesh();
+
+  vec3 v0, v3;
+  physicsShapeMeshGetVertex(&mesh, 0, v0);
+  physicsShapeMeshGetVertex(&mesh, 3, v3);
+
+  assert_float_equal(v0[0], -5.0f, 0.0001f);
+  assert_float_equal(v0[2], -5.0f, 0.0001f);
+  assert_float_equal(v3[0], -5.0f, 0.0001f);
+  assert_float_equal(v3[2], -5.0f, 0.0001f);
+
+  assert_int_equal(memoryGetAllocatedCount(), 0);
+}
+
+// Vertex layout matching a typical interleaved render vertex (uv then
+// pos), to prove the stride-based reader can point straight at a render
+// buffer instead of a dedicated physics copy.
+typedef struct {
+  float_t uv[2];
+  float_t pos[3];
+} testInterleavedVertex_t;
+
+static void test_supportsInterleavedRenderVertexLayout(void **state) {
+  testInterleavedVertex_t vertices[3] = {
+    { .uv = { 0, 0 }, .pos = { -5.0f, 0.0f, -5.0f } },
+    { .uv = { 1, 0 }, .pos = {  5.0f, 0.0f, -5.0f } },
+    { .uv = { 0, 1 }, .pos = { -5.0f, 0.0f,  5.0f } },
+  };
+  physicsshapemesh_t mesh = {
+    .vertices = (const uint8_t *)vertices[0].pos,
+    .stride = sizeof(testInterleavedVertex_t),
+    .triangleCount = 1
+  };
+
+  vec3 v1;
+  physicsShapeMeshGetVertex(&mesh, 1, v1);
+  assert_float_equal(v1[0], 5.0f, 0.0001f);
+  assert_float_equal(v1[2], -5.0f, 0.0001f);
+
+  assert_int_equal(memoryGetAllocatedCount(), 0);
+}
+
+static void test_sphereRestingOnMesh(void **state) {
+  physicsshapemesh_t mesh = flatGroundMesh();
+  vec3 meshPos = { 0.0f, 0.0f, 0.0f };
+
+  // Sphere overlapping the ground by 0.2.
+  vec3 sphereCenter = { 0.0f, 0.3f, 0.0f };
+  vec3 normal; float_t depth;
+  assert_true(physicsShapeMeshTestSphere(
+    &mesh, meshPos, sphereCenter, 0.5f, normal, &depth
+  ));
+  assert_float_equal(depth, 0.2f, 0.0001f);
+  assert_float_equal(normal[1], 1.0f, 0.0001f); // pushes sphere up
+
+  // Far above: no overlap.
+  vec3 sphereFar = { 0.0f, 10.0f, 0.0f };
+  assert_false(physicsShapeMeshTestSphere(
+    &mesh, meshPos, sphereFar, 0.5f, normal, &depth
+  ));
+
+  // Offsetting the mesh's own position shifts the ground with it: raising
+  // both the ground and the sphere together reproduces the same overlap.
+  vec3 meshPosRaised = { 0.0f, 1.0f, 0.0f };
+  vec3 sphereCenterRaised = { 0.0f, 1.3f, 0.0f };
+  assert_true(physicsShapeMeshTestSphere(
+    &mesh, meshPosRaised, sphereCenterRaised, 0.5f, normal, &depth
+  ));
+  assert_float_equal(depth, 0.2f, 0.0001f);
+
+  // But the sphere no longer overlaps the ground at its old (un-raised)
+  // height, since the ground moved out from under it.
+  assert_false(physicsShapeMeshTestSphere(
+    &mesh, meshPosRaised, sphereCenter, 0.5f, normal, &depth
+  ));
+
+  assert_int_equal(memoryGetAllocatedCount(), 0);
+}
+
+static void test_capsuleRestingOnMesh(void **state) {
+  physicsshapemesh_t mesh = flatGroundMesh();
+  vec3 meshPos = { 0.0f, 0.0f, 0.0f };
+
+  // Standing capsule (half-height 1) whose bottom cap dips 0.1 into the
+  // ground: center at y = radius + halfHeight - 0.1.
+  const float_t radius = 0.5f;
+  const float_t halfHeight = 1.0f;
+  vec3 capsuleCenter = { 0.0f, radius + halfHeight - 0.1f, 0.0f };
+
+  vec3 normal; float_t depth;
+  assert_true(physicsShapeMeshTestCapsule(
+    &mesh, meshPos, capsuleCenter, radius, halfHeight, normal, &depth
+  ));
+  assert_float_equal(depth, 0.1f, 0.001f);
+  assert_float_equal(normal[1], 1.0f, 0.0001f);
+
+  // Lifted well clear of the ground: no overlap.
+  vec3 capsuleHigh = { 0.0f, 10.0f, 0.0f };
+  assert_false(physicsShapeMeshTestCapsule(
+    &mesh, meshPos, capsuleHigh, radius, halfHeight, normal, &depth
+  ));
+
+  assert_int_equal(memoryGetAllocatedCount(), 0);
+}
+
+static void test_cubeIsUnsupported(void **state) {
+  physicsshapemesh_t mesh = flatGroundMesh();
+  vec3 meshPos = { 0.0f, 0.0f, 0.0f };
+
+  physicsshape_t cube = {
+    .type = PHYSICS_SHAPE_CUBE,
+    .data.cube.halfExtents = { 0.5f, 0.5f, 0.5f }
+  };
+  vec3 cubePos = { 0.0f, 0.3f, 0.0f };
+  vec3 normal; float_t depth;
+  assert_false(physicsShapeMeshTest(
+    meshPos, &mesh, cubePos, &cube, normal, &depth
+  ));
+
+  assert_int_equal(memoryGetAllocatedCount(), 0);
+}
+
+static void test_physicsShapeMeshCreateIntegratesWithDispatch(void **state) {
+  physicsshapemesh_t mesh = flatGroundMesh();
+  physicsshape_t landscape = physicsShapeMeshCreate(&mesh);
+  assert_int_equal(landscape.type, PHYSICS_SHAPE_CUSTOM);
+
+  physicsshape_t sphere = {
+    .type = PHYSICS_SHAPE_SPHERE,
+    .data.sphere.radius = 0.5f
+  };
+  vec3 meshPos = { 0.0f, 0.0f, 0.0f };
+  vec3 sphereCenter = { 0.0f, 0.3f, 0.0f };
+
+  // Landscape as B, matching physicsWorldStep's dynamic(A)-vs-static(B).
+  vec3 normal; float_t depth;
+  assert_true(physicsTestShapeVsShape(
+    sphereCenter, sphere, meshPos, landscape, normal, &depth
+  ));
+  assert_float_equal(depth, 0.2f, 0.0001f);
+  assert_float_equal(normal[1], 1.0f, 0.0001f);
+
+  assert_int_equal(memoryGetAllocatedCount(), 0);
+}
+
+int main(int argc, char **argv) {
+  const struct CMUnitTest tests[] = {
+    cmocka_unit_test(test_getVertexReadsRawPositions),
+    cmocka_unit_test(test_supportsInterleavedRenderVertexLayout),
+    cmocka_unit_test(test_sphereRestingOnMesh),
+    cmocka_unit_test(test_capsuleRestingOnMesh),
+    cmocka_unit_test(test_cubeIsUnsupported),
+    cmocka_unit_test(test_physicsShapeMeshCreateIntegratesWithDispatch),
+  };
+
+  return cmocka_run_group_tests(tests, NULL, NULL);
+}
diff --git a/test/scene/test_scene.c b/test/scene/test_scene.c
index 879f13da..94eef9c6 100644
--- a/test/scene/test_scene.c
+++ b/test/scene/test_scene.c
@@ -12,6 +12,7 @@
 #include "entity/entitymanager.h"
 
 static void countingUpdateCallback(
+  entitymanager_t *mgr,
   const entityid_t entityId,
   const componentid_t componentId,
   void *user
@@ -58,10 +59,9 @@ static void test_sceneEntitiesAreIsolatedPerScene(void **state) {
   assert_int_equal(memoryGetAllocatedCount(), 0);
 }
 
-static void test_sceneUpdateOnlyTicksActiveScene(void **state) {
+static void test_sceneFixedUpdateOnlyTicksActiveScene(void **state) {
   sceneInit();
   timeInit();
-  TIME.dynamicUpdate = true;
 
   sceneid_t sceneA = sceneCreate();
   sceneid_t sceneB = sceneCreate();
@@ -84,13 +84,13 @@ static void test_sceneUpdateOnlyTicksActiveScene(void **state) {
   );
 
   sceneSetActive(sceneA);
-  sceneUpdate();
+  sceneFixedUpdate();
 
   assert_int_equal(counterA, 1);
   assert_int_equal(counterB, 0);
 
   sceneSetActive(sceneB);
-  sceneUpdate();
+  sceneFixedUpdate();
 
   assert_int_equal(counterA, 1);
   assert_int_equal(counterB, 1);
@@ -99,6 +99,44 @@ static void test_sceneUpdateOnlyTicksActiveScene(void **state) {
   assert_int_equal(memoryGetAllocatedCount(), 0);
 }
 
+static void test_sceneUpdateOnlyRunsFixedUpdateOnNonDynamicFrames(void **state) {
+  sceneInit();
+  timeInit();
+
+  sceneid_t scene = sceneCreate();
+  sceneSetActive(scene);
+
+  uint32_t counter = 0;
+  entitymanager_t *entities = sceneGetEntities(scene);
+  entityid_t entity = entityManagerAdd(entities);
+  entityUpdateAdd(
+    entities, entity, countingUpdateCallback, COMPONENT_ID_INVALID, &counter
+  );
+
+  #if DUSK_TIME_DYNAMIC
+    // Still accumulating toward the next fixed timestep: sceneUpdate must
+    // not run sceneFixedUpdate yet.
+    TIME.dynamicUpdate = true;
+    sceneUpdate();
+    assert_int_equal(counter, 0);
+
+    // A fixed timestep boundary was just crossed: sceneUpdate must run
+    // sceneFixedUpdate exactly once.
+    TIME.dynamicUpdate = false;
+    sceneUpdate();
+    assert_int_equal(counter, 1);
+  #else
+    // Non-dynamic-time platforms: every frame is a fixed timestep.
+    sceneUpdate();
+    assert_int_equal(counter, 1);
+    sceneUpdate();
+    assert_int_equal(counter, 2);
+  #endif
+
+  sceneDispose();
+  assert_int_equal(memoryGetAllocatedCount(), 0);
+}
+
 static void test_sceneDestroyClearsActive(void **state) {
   sceneInit();
 
@@ -117,7 +155,8 @@ int main(int argc, char **argv) {
   const struct CMUnitTest tests[] = {
     cmocka_unit_test(test_sceneCreateDestroy),
     cmocka_unit_test(test_sceneEntitiesAreIsolatedPerScene),
-    cmocka_unit_test(test_sceneUpdateOnlyTicksActiveScene),
+    cmocka_unit_test(test_sceneFixedUpdateOnlyTicksActiveScene),
+    cmocka_unit_test(test_sceneUpdateOnlyRunsFixedUpdateOnNonDynamicFrames),
     cmocka_unit_test(test_sceneDestroyClearsActive),
   };