docs: sync widget.luau in plan with review fixes

docs/superpowers/plans/2026-08-31-headsetcontrol-plugin.md

@@ -610,7 +610,7 @@ local function batteryGlyph()
 end
 
 local function batteryColor()
-  local low = noctalia.getConfig("battery_low")
+  local low = noctalia.getConfig("battery_low") or 20
   if battery.level < 0 then return "#6e7681" end
   if battery.level <= low then return "#e5484d" end
   if battery.status == "BATTERY_CHARGING" then return "#3fb950" end
@@ -618,6 +618,7 @@ local function batteryColor()
 end
 
 local function render()
+  if not barWidget then return end
   if errorState == "no_binary" then
     barWidget.setGlyph("alert-triangle")
     barWidget.setColor("#e5484d")
@@ -661,8 +662,14 @@ end
 
 local function sendSidetone(value)
   value = math.clamp(value, 0, 128)
+  local previous = sidetoneValue
   hsc.sendCommand({ "-s", tostring(value) }, function(res)
     if res.exitCode ~= 0 then
+      if previous ~= nil then
+        sidetoneValue = previous
+      end
+      sidetoneFlashUntil = 0
+      render()
       noctalia.notifyError(noctalia.tr("error.command_failed"), string.sub(res.stderr or "", 1, 200))
       return
     end
@@ -675,7 +682,8 @@ end
 
 function onScroll(axis, steps)
   if axis ~= "vertical" then return end
-  local current = sidetoneValue or noctalia.getConfig("sidetone_default")
+  if not caps.sidetone or errorState ~= "" then return end
+  local current = sidetoneValue or noctalia.getConfig("sidetone_default") or 64
   sendSidetone(current + steps * 4)
 end
 
@@ -711,6 +719,7 @@ noctalia.state.watch("error", function(v) errorState = v or ""; render() end)
 noctalia.state.watch("sidetone", function(v) if v ~= nil then sidetoneValue = v end end)
 
 syncState()
+render()
 ```
 
 - [ ] **Step 2: Verify the widget loads (hot-reload)**