docs: add haptic

Author: skim0119

docs/virtual_field/adding_character.md

@@ -8,6 +8,7 @@ This page is the entry point for the character-implementation tutorials.
 dual_arm_overview
 dual_arm_inputs
 dual_arm_assets
+haptic
 ```
 
 The current runtime contract is still centered around dual-arm simulator

docs/virtual_field/communication_scheme.md

@@ -53,7 +53,7 @@ Example for a VR client:
   "version": 1,
   "type": "hello",
   "payload": {
-    "client": "bsr-webxr",
+    "client": "sparc-webxr",
     "role": "vr_client",
     "requested_arm_count": 2,
     "character_mode": "spirobs"
@@ -259,7 +259,8 @@ Top-level payload shape:
   "user_arms": {},
   "meshes": {},
   "overlay_points": {},
-  "spheres": {}
+  "spheres": {},
+  "haptics": []
 }
 ```
 
@@ -334,6 +335,19 @@ Each sphere contains:
 - `color_rgb`
 - `visible`
 
+### `haptics`
+
+`haptics` is a list of haptic events for VR controllers.
+
+Each event contains:
+
+- `arm_id`
+- `active`
+- `intensity`
+
+The backend gathers these events from each simulation by calling
+`simulation.haptic_events()` before publishing `scene_state`.
+
 ## Publisher messages
 
 The `publisher` role is used by Python-side or external tools that inject scene

docs/virtual_field/octo_arm_overview.md

@@ -26,7 +26,6 @@ It currently helps with:
 
 - storing the ordered `arm_ids`
 - assigning each arm id to one entry in `base_positions`
-- exposing convenience helpers such as `rod_for_index()` and `target_for_index()`
 - keeping the mode aligned with the rest of the runtime publishing pipeline
 
 The key requirement is that a derived simulation must provide eight base