diff --git a/Makefile b/Makefile
index 95eccfe..d5ce0ce 100644
--- a/Makefile
+++ b/Makefile
@@ -5,7 +5,7 @@ LUA ?= lua
 CXX ?= c++
 CXXFLAGS ?= -std=c++11 -Wall -Wextra
 BUILD_DIR := .pio/build/esp32-32e
-LUA_TESTS := test/ui_layout.lua test/ui_theme.lua test/settings_calibration.lua
+LUA_TESTS := test/ui_layout.lua test/ui_theme.lua test/settings_calibration.lua test/statusbar_dirty.lua
 
 .PHONY: test test-lua test-cpp test-stubs stubs build upload monitor clean
 
diff --git a/README.md b/README.md
index 4fca358..f1d5a9e 100644
--- a/README.md
+++ b/README.md
@@ -51,12 +51,18 @@ button in the status bar does too.
 
 | Module | Functions |
 |---|---|
-| `gui` | `width()`, `height()`, `clear(color)`, `fillRect(x,y,w,h,c)`, `drawRect(x,y,w,h,c)`, `fillCircle(x,y,r,c,bg)`, `drawLine(x1,y1,x2,y2,c)`, `drawText(text,x,y,fg,bg)`, `roundRect(x,y,w,h,radius,bg,top,bottom,border)`, `fontHeight()`, `textWidth(text)`, `setRotation(0-3)`, `color(r,g,b)` |
-| `input` | `getTouch()` -> `x,y` or nil, `getRawTouch()` -> raw ADC `x,y` or nil, `touched()` |
+| `gui` | `getWidth()`, `getHeight()`, `clear(color)`, `fillRect(x,y,w,h,c)`, `drawRect(x,y,w,h,c)`, `fillCircle(x,y,r,c,bg)`, `drawLine(x1,y1,x2,y2,c)`, `drawText(text,x,y,fg,bg)`, `roundRect(x,y,w,h,radius,bg,top,bottom,border)`, `getFontHeight()`, `getTextWidth(text)`, `getRotation()`, `setRotation(deg)`, `setFullscreen(on)`, `color(r,g,b)` |
+| `input` | `getTouch()` -> `x,y` or nil, `getRawTouch()` -> raw ADC `x,y` or nil, `isTouched()` |
 | `fs` | `readFile(path)`, `writeFile(path, data)`, `exists(path)`, `listFiles(path)`, `listDirs(path)` |
-| `sys` | `millis()`, `exit()`, `launch(path)`, `setCalibration(x0,y0,x1,y1)`, `getRotation()`, `setRotation(deg)`, `getTheme()`, `setTheme(name)` |
-| `wifi` | `scan()` -> `{ssid,rssi,secure}[]`, `connect(ssid,password)`, `status()` -> `{state,ssid,ip,rssi}`, `forget()` |
-| `log` | `info(msg)` (serial) |
+| `sys` | `getMillis()`, `delay(ms)`, `exit()`, `launch(path)`, `getAppName()`, `getMemory()` -> `free,total`, `isClockSynced()`, `setTickInterval(ms)` |
+| `settings` | `getRotation()`, `setRotation(deg)`, `getTheme()`, `setTheme(name)`, `getTimezone()`, `setTimezone(tz)`, `setCalibration(x0,y0,x1,y1)` |
+| `wifi` | `scan()` -> `{ssid,rssi,secure}[]`, `connect(ssid,password)`, `getStatus()` -> `{state,ssid,ip,rssi}`, `getLocalIP()`, `isConnected()`, `disconnect()`, `forget()` |
+| `log` | `debug(msg)`, `info(msg)`, `error(msg)` (serial) |
+
+Accessors are `getName` / `setName` / `isName`; bare names are actions (`gui.fillRect`)
+or pure conversions (`gui.color`, `http.urlencode`). `settings.*` is persisted user
+intent; `gui.getRotation()` is the frame actually being drawn, which differs while an
+app rotates the panel transiently.
 
 Colors are RGB565 integers; build them with `gui.color(r, g, b)`.
 
@@ -76,7 +82,7 @@ return {
 ```
 
 Missing file means the built-in defaults are used. `apps/settings` walks two
-crosshairs and saves the result via `sys.setCalibration()`, cycles `rotation`
+crosshairs and saves the result via `settings.setCalibration()`, cycles `rotation`
 through 0, 90, 180 and 270 degrees, and scans/selects Wi-Fi networks with an
 on-screen password keyboard. A saved network reconnects at boot.
 
@@ -85,7 +91,7 @@ card like any other device containing a saved password.
 
 Rotation never needs a recalibration: calibration is stored in the panel's
 rotation-0 frame (320x480 raw ADC space) and the current rotation is applied
-afterwards, so `sys.setRotation()` is safe at any time. `gui.setRotation(0-3)`
+afterwards, so `settings.setRotation()` is safe at any time. `gui.setRotation(degrees)`
 changes only the current frame; the firmware restores the saved rotation when an
 app exits. The glass itself is always portrait, so a rotated UI is drawn
 sideways on it.
diff --git a/docs/lua-api-parity.md b/docs/lua-api-parity.md
index 91ae927..ca087c8 100644
--- a/docs/lua-api-parity.md
+++ b/docs/lua-api-parity.md
@@ -10,13 +10,13 @@ Compared against crosspoint-reader at `src/util/lua/LuaBindings*.cpp`.
 ## Identical
 
 `fs.listDirs`, `fs.listFiles`, `fs.exists`, `fs.readFile`, `fs.writeFile`,
-`gui.width`, `gui.height`, `gui.fillRect`, `gui.drawRect`, `gui.drawLine`,
-`sys.millis`, `sys.delay`, `sys.exit`, `log.debug/info/error`, the whole `http` table,
-`sys.setTickInterval`, `wifi.status`, `wifi.isConnected`, `wifi.localIP`, and the
+`gui.getWidth`, `gui.getHeight`, `gui.fillRect`, `gui.drawRect`, `gui.drawLine`,
+`sys.getMillis`, `sys.delay`, `sys.exit`, `log.debug/info/error`, the whole `http` table,
+`sys.setTickInterval`, `wifi.getStatus`, `wifi.isConnected`, `wifi.getLocalIP`, and the
 `init()` / `draw()` / `on_tick()` callbacks. `init()` is required in both, so a
 misspelled entry point is an error rather than an app that quietly draws nothing.
 
-`wifi.status()` returns `{state, ssid, ip, rssi}` in both. crosspoint returned a bare
+`wifi.getStatus()` returns `{state, ssid, ip, rssi}` in both. crosspoint returned a bare
 string until this was reconciled; a string had nowhere to put the address and signal
 strength a status screen wants. Its `state` vocabulary is a subset: crosspoint reports
 `disconnected`, `connecting`, `connected` and `failed`, while this firmware adds
@@ -27,13 +27,13 @@ strength a status screen wants. Its `state` vocabulary is a subset: crosspoint r
 | Area | crosspoint-reader | slate32 | Why |
 |---|---|---|---|
 | Input | `input.wasPressed(button)` and friends, 8 named buttons | `input.getTouch`, `getRawTouch`, `touched` | Different hardware. A touch panel has no button names and a button device has no coordinates. |
-| Drawing | `gui.drawText(font, x, y, text, color, style)`, `getTextWidth(font, text)` | `gui.drawText(text, x, y, color, bg)`, `textWidth(text)` | crosspoint ships several fonts; this firmware has one built-in font scaled by `gui.setTextSize(n)`, and needs an opaque background colour because the panel is not e-ink. |
+| Drawing | `gui.drawText(font, x, y, text, color, style)`, `getTextWidth(font, text)` | `gui.drawText(text, x, y, color, bg)`, `gui.getTextWidth(text)` | crosspoint ships several fonts; this firmware has one built-in font scaled by `gui.setTextSize(n)`, and needs an opaque background colour because the panel is not e-ink. |
 | Refresh | `gui.refresh(mode)`, `REFRESH_FULL/HALF/FAST` | none | An LCD has no waveform modes. |
 | Colour | `COLOR_*` constants, 4 grey levels | `gui.color(r, g, b)` returning RGB565 | 16-bit colour has too many values to enumerate. |
 | Shapes | `drawRoundedRect` + `fillRoundedRect` | one `gui.roundRect(...)` with gradient and border | Fill and border derive from a single distance field, so their edges cannot disagree. |
-| Themes | none | `sys.getTheme/setTheme`, `/lib/theme.lua` | Colour panel. |
-| Rotation | `gui.setOrientation("portrait")` | `sys.setRotation(degrees)` persisted, `gui.setRotation(0-3)` for one frame | This device stores rotation in settings and remaps touch to match. |
-| Clock | nothing exposed; UTC offset is a C++ setting | `sys.clockSynced`, `sys.getTimezone/setTimezone` with POSIX TZ rules | Timezone here is a stored rule, so `os.date()` returns local time with DST handled by libc. |
+| Themes | none | `settings.getTheme/setTheme`, `/lib/theme.lua` | Colour panel. |
+| Rotation | `gui.setOrientation("portrait")` | `settings.setRotation(degrees)` persisted, `gui.setRotation(degrees)` for one frame | This device stores rotation in settings and remaps touch to match. |
+| Clock | nothing exposed; UTC offset is a C++ setting | `sys.isClockSynced`, `settings.getTimezone/setTimezone` with POSIX TZ rules | Timezone here is a stored rule, so `os.date()` returns local time with DST handled by libc. |
 | Launching | launcher is C++ | `sys.launch(path)`, home is a Lua app | The launcher is just another app here, named `home`. |
 | Modules | single-file apps; `require` unusable | `require` works, `package.searchers` reads the SD card, `/lib` on the path | Shared code such as `ui.lua` needs it. **crosspoint should adopt this.** |
 | BLE | `ble.*` | none | No BLE use case here yet. |
diff --git a/sdcard/apps/hello/main.lua b/sdcard/apps/hello/main.lua
index 7feba52..a1b0d0c 100644
--- a/sdcard/apps/hello/main.lua
+++ b/sdcard/apps/hello/main.lua
@@ -9,7 +9,7 @@ function init()
   gui.clear(theme.bg)
   gui.drawText("hello from sd card", 10, 10, theme.fg, theme.bg)
   gui.drawText("touch the screen", 10, 30, theme.muted, theme.bg)
-  log.info("hello app started, screen " .. gui.width() .. "x" .. gui.height())
+  log.info("hello app started, screen " .. gui.getWidth() .. "x" .. gui.getHeight())
 end
 
 function on_tick()
diff --git a/sdcard/apps/settings/main.lua b/sdcard/apps/settings/main.lua
index df73ccd..02b83a7 100644
--- a/sdcard/apps/settings/main.lua
+++ b/sdcard/apps/settings/main.lua
@@ -1,4 +1,7 @@
 local ui = require("ui")
+-- The same module instance the firmware paints the bar with, so toggling fullscreen
+-- through it drops the cache that would otherwise hide the repaint.
+local statusbar = require("statusbar")
 
 local INSET = 30
 local MENU_PAD, MENU_GAP = 12, 8
@@ -50,11 +53,11 @@ local function drawTarget(n)
 end
 
 local function finishCalibration()
-  local ok = sys.setCalibration(computeCalibration(samples[1], samples[2], 320, 480, INSET))
+  local ok = settings.setCalibration(computeCalibration(samples[1], samples[2], 320, 480, INSET))
   message = ok and "calibration saved" or "save failed"
   mode = "menu"
-  gui.setRotation(sys.getRotation() / 90)
-  gui.fullscreen(false)
+  gui.setRotation(settings.getRotation())
+  statusbar.setFullscreen(false)
   buildMenu()
 end
 
@@ -65,12 +68,12 @@ function startCalibration()
   gui.setRotation(0)
   -- The targets sit at the physical corners and the samples are read in panel
   -- coordinates, so the status bar cannot be allowed to shift the frame.
-  gui.fullscreen(true)
+  statusbar.setFullscreen(true)
   drawTarget(1)
 end
 
 function cycleRotation()
-  local ok = sys.setRotation((sys.getRotation() + 90) % 360)
+  local ok = settings.setRotation((settings.getRotation() + 90) % 360)
   message = ok and "rotation saved" or "save failed"
   buildMenu()
 end
@@ -81,8 +84,7 @@ local function cycleTheme()
   for index, name in ipairs(names) do
     if name == ui.themeName then next_index = index % #names + 1 end
   end
-  local ok = sys.setTheme(names[next_index])
-  ui.reloadTheme()
+  local ok = ui.setTheme(names[next_index])
   message = ok and "theme saved" or "save failed"
   buildMenu()
 end
@@ -92,7 +94,7 @@ local zones = require("timezones")
 -- The stored value is a POSIX rule, so a zone set by hand and missing from the list
 -- shows its rule rather than pretending to be the first entry.
 local function zoneLabel()
-  local current = sys.getTimezone()
+  local current = settings.getTimezone()
   for _, zone in ipairs(zones) do
     if zone.tz == current then return zone.name end
   end
@@ -100,12 +102,12 @@ local function zoneLabel()
 end
 
 local function cycleTimezone()
-  local current = sys.getTimezone()
+  local current = settings.getTimezone()
   local next_index = 1
   for index, zone in ipairs(zones) do
     if zone.tz == current then next_index = index % #zones + 1 end
   end
-  local ok = sys.setTimezone(zones[next_index].tz)
+  local ok = settings.setTimezone(zones[next_index].tz)
   message = ok and "timezone saved" or "save failed"
   buildMenu()
 end
@@ -134,8 +136,8 @@ function buildMenu()
   local side, cols = ui.cardSide(6, MENU_PAD, MENU_GAP, message and 20 or 0)
   local cards = {
     card(side, "calibrate", "touch", startCalibration),
-    card(side, "rotation", sys.getRotation() .. " deg", cycleRotation),
-    card(side, "wifi", wifiValue(wifi.status()), buildWifi),
+    card(side, "rotation", settings.getRotation() .. " deg", cycleRotation),
+    card(side, "wifi", wifiValue(wifi.getStatus()), buildWifi),
     card(side, "theme", ui.themeName, cycleTheme),
     card(side, "timezone", zoneLabel(), cycleTimezone),
     card(side, "exit", nil, sys.exit),
@@ -169,7 +171,7 @@ end
 local function confirmForget()
   dialog = ui.confirm{
     title = "forget network?",
-    message = wifi.status().ssid,
+    message = wifi.getStatus().ssid,
     ok = "forget",
     on_ok = forgetNetwork,
     on_cancel = function()
@@ -182,7 +184,7 @@ end
 
 function buildWifi()
   mode = "wifi"
-  local status = wifi.status()
+  local status = wifi.getStatus()
   local items = {pad = 12, gap = 8, ui.text("wifi"), ui.text("wifi: " .. wifiValue(status))}
   if status.state == "connected" then
     items[#items + 1] = ui.text("ip: " .. status.ip)
@@ -272,8 +274,8 @@ local function drawKey(node, label, x, y, w)
   local gradient = node.gradient
   local top, bottom = gradient[1], gradient[2]
   gui.roundRect(x, y, w, KEY_H, node.radius, node.bg, top, bottom, node.color)
-  gui.drawText(label, x + math.floor((w - gui.textWidth(label)) / 2),
-               y + math.floor((KEY_H - gui.fontHeight()) / 2), node.color, bottom)
+  gui.drawText(label, x + math.floor((w - gui.getTextWidth(label)) / 2),
+               y + math.floor((KEY_H - gui.getFontHeight()) / 2), node.color, bottom)
 end
 
 local function paintKeyboard(node)
@@ -382,7 +384,7 @@ function on_tick()
     return
   end
   if mode == "connecting" then
-    local status = wifi.status()
+    local status = wifi.getStatus()
     if status.state == "connected" then
       message = "connected: " .. status.ip
       buildWifi()
diff --git a/sdcard/lib/statusbar.lua b/sdcard/lib/statusbar.lua
index 409dcd0..576e925 100644
--- a/sdcard/lib/statusbar.lua
+++ b/sdcard/lib/statusbar.lua
@@ -1,6 +1,9 @@
 -- The top bar, painted by the firmware once a second in every app. It draws in panel
--- coordinates (the firmware drops the app viewport around the call), so gui.width()
+-- coordinates (the firmware drops the app viewport around the call), so gui.getWidth()
 -- here is the whole screen.
+--
+-- Invalidation is entirely local: draw() compares what it is about to paint against what
+-- it last painted, so the firmware never has to tell the bar that anything changed.
 
 local ui = require("ui")
 
@@ -10,18 +13,31 @@ local PAD = 6
 -- often it calls draw().
 local M = {height = 22, interval = 1000}
 local BAR_H = M.height
+local SIGNAL_W = 11
+local GAP = 8
+
+-- What is currently on the panel. Every field repaints only when its value changes, so
+-- the once-a-second tick costs one clock rectangle instead of a whole bar.
+local shown = {}
 
 local function clock()
-  return sys.clockSynced() and os.date("%H:%M") or "--:--"
+  return sys.isClockSynced() and os.date("%H:%M:%S") or "--:--:--"
+end
+
+local function signalBars()
+  local status = wifi.getStatus()
+  if status.state ~= "connected" then return 0 end
+  return status.rssi >= -60 and 3 or status.rssi >= -75 and 2 or 1
+end
+
+local function memPercent()
+  local free, total = sys.getMemory()
+  if not total or total <= 0 then return 0 end
+  return (total - free) * 100 // total
 end
 
 -- Bars rather than glyphs: there is no icon font, and signal strength is a scale.
-local function drawSignal(x, y, color, muted)
-  local status = wifi.status()
-  local bars = 0
-  if status.state == "connected" then
-    bars = status.rssi >= -60 and 3 or status.rssi >= -75 and 2 or 1
-  end
+local function drawSignal(x, y, bars, color, muted)
   for i = 1, 3 do
     local h = i * 3
     gui.fillRect(x + (i - 1) * 4, y + 9 - h, 3, h, i <= bars and color or muted)
@@ -42,24 +58,62 @@ local function drawHome(theme)
   end
 end
 
+-- Leaving fullscreen is the one change the bar cannot observe: no draw happens while an
+-- app owns the panel, so the state it last painted still matches the state it would paint
+-- now, while the pixels are gone. Apps toggle fullscreen through here for that reason.
+function M.setFullscreen(on)
+  gui.setFullscreen(on)
+  if not on then shown = {} end
+end
+
 function M.draw(home)
   local theme = ui.theme
   gui.setTextSize(1)  -- panel state: the app may have left it scaled up
-  local w = gui.width()
-  gui.fillRect(0, 0, w, BAR_H, theme.bg)
-  gui.fillRect(0, BAR_H - 1, w, 1, theme.muted)  -- a rule, so the bar reads as chrome
+  local w = gui.getWidth()
+  local textY = math.floor((BAR_H - 1 - gui.getFontHeight()) / 2)
 
-  local textY = math.floor((BAR_H - 1 - gui.fontHeight()) / 2)
-  local nameX = PAD
-  if home then
-    drawHome(theme)
-    nameX = BAR_H + PAD
+  -- Slots sized for their widest value, so a shorter one never shifts its neighbours.
+  local clockW, memW = gui.getTextWidth("00:00:00"), gui.getTextWidth("100%")
+  local clockX = w - PAD - clockW
+  local signalX = clockX - GAP - SIGNAL_W
+  local memX = signalX - GAP - memW
+
+  -- Rotation moves every slot and the theme recolors them; a new app gets a fresh Lua
+  -- state, so an empty cache already means "repaint everything".
+  local key = gui.getRotation() .. "|" .. ui.themeName
+  if key ~= shown.key then
+    shown = {key = key}
+    gui.fillRect(0, 0, w, BAR_H, theme.bg)
+    gui.fillRect(0, BAR_H - 1, w, 1, theme.muted)  -- a rule, so the bar reads as chrome
+    local nameX = PAD
+    if home then
+      drawHome(theme)
+      nameX = BAR_H + PAD
+    end
+    gui.drawText(sys.getAppName(), nameX, textY, theme.fg, theme.bg)
+  end
+
+  local mem = memPercent()
+  if mem ~= shown.mem then
+    shown.mem = mem
+    local text = mem .. "%"
+    gui.fillRect(memX, 0, memW, BAR_H - 1, theme.bg)
+    gui.drawText(text, memX + memW - gui.getTextWidth(text), textY, theme.muted, theme.bg)
+  end
+
+  local bars = signalBars()
+  if bars ~= shown.bars then
+    shown.bars = bars
+    gui.fillRect(signalX, 0, SIGNAL_W, BAR_H - 1, theme.bg)
+    drawSignal(signalX, textY, bars, theme.fg, theme.muted)
   end
-  gui.drawText(sys.appName(), nameX, textY, theme.fg, theme.bg)
 
   local time = clock()
-  gui.drawText(time, w - PAD - gui.textWidth(time), textY, theme.muted, theme.bg)
-  drawSignal(w - PAD - gui.textWidth(time) - 8 - 11, textY, theme.fg, theme.muted)
+  if time ~= shown.time then
+    shown.time = time
+    gui.fillRect(clockX, 0, clockW, BAR_H - 1, theme.bg)
+    gui.drawText(time, clockX, textY, theme.muted, theme.bg)
+  end
 end
 
 return M
diff --git a/sdcard/lib/ui.lua b/sdcard/lib/ui.lua
index c304d13..4bab05c 100644
--- a/sdcard/lib/ui.lua
+++ b/sdcard/lib/ui.lua
@@ -86,10 +86,18 @@ function ui.themeNames()
   return names
 end
 
--- Re-read the saved theme. Called at load, and again by the settings app so a
--- changed theme takes effect without relaunching.
+-- Saves the theme and reloads the palette. The firmware stores only the name and cannot
+-- call back into Lua, so this is the seam that keeps the two halves from drifting.
+function ui.setTheme(name)
+  local ok = settings.setTheme(name)
+  ui.reloadTheme()
+  return ok
+end
+
+-- Re-read the saved theme. Called at load, and by ui.setTheme(), so a changed theme takes
+-- effect without relaunching.
 function ui.reloadTheme()
-  ui.themeName = sys.getTheme and sys.getTheme() or "light"
+  ui.themeName = settings.getTheme and settings.getTheme() or "light"
   local available = themes()
   local seed = available[ui.themeName] or available.light or FALLBACK
   ui.theme = palette(seed)
@@ -319,8 +327,8 @@ end
 -- neighbour at another size would otherwise decide this node's metrics.
 local function measureText(self, available)
   gui.setTextSize(self.size or 1)
-  self.mw = resolve(self.w, available.w, "width") or gui.textWidth(self.label)
-  self.mh = resolve(self.h, available.h, "height") or gui.fontHeight()
+  self.mw = resolve(self.w, available.w, "width") or gui.getTextWidth(self.label)
+  self.mh = resolve(self.h, available.h, "height") or gui.getFontHeight()
   return self.mw, self.mh
 end
 
@@ -350,10 +358,10 @@ end
 -- cannot be tapped. `reserve` is height the caller needs for anything under the grid.
 -- ponytail: enough cards make them unusably small; that is the point to add scrolling.
 function ui.cardSide(count, pad, gap, reserve)
-  local cols = gui.width() >= gui.height() and 3 or 2
+  local cols = gui.getWidth() >= gui.getHeight() and 3 or 2
   local rows = math.ceil(count / cols)
-  local byWidth = (gui.width() - 2 * pad - (cols - 1) * gap) // cols
-  local byHeight = (gui.height() - 2 * pad - (reserve or 0) - (rows - 1) * gap) // rows
+  local byWidth = (gui.getWidth() - 2 * pad - (cols - 1) * gap) // cols
+  local byHeight = (gui.getHeight() - 2 * pad - (reserve or 0) - (rows - 1) * gap) // rows
   return math.min(byWidth, byHeight), cols
 end
 
@@ -363,11 +371,11 @@ end
 function ui.label(text, spec)
   spec = spec or {}
   gui.setTextSize(spec.size or 1)
-  if spec.fit and gui.textWidth(text) > spec.fit then
-    while #text > 1 and gui.textWidth(text .. "~") > spec.fit do text = text:sub(1, -2) end
+  if spec.fit and gui.getTextWidth(text) > spec.fit then
+    while #text > 1 and gui.getTextWidth(text .. "~") > spec.fit do text = text:sub(1, -2) end
     text = text .. "~"
   end
-  spec.w, spec.fit = gui.textWidth(text), nil
+  spec.w, spec.fit = gui.getTextWidth(text), nil
   return ui.text(text, spec)
 end
 
@@ -464,7 +472,7 @@ function ui.screen(root, style)
 end
 
 function Screen:relayout()
-  local rect = {x = 0, y = 0, w = gui.width(), h = gui.height()}
+  local rect = {x = 0, y = 0, w = gui.getWidth(), h = gui.getHeight()}
   self.root:measure(rect)
   self.root:place(rect)
   gui.clear(self.root.bg)
@@ -473,7 +481,7 @@ end
 function Screen:draw()
   self.root:draw()
   -- Hold the pressed look briefly so a fast tap is still perceptible.
-  if self.released and sys.millis() - self.pressedAt >= PRESS_MS then
+  if self.released and sys.getMillis() - self.pressedAt >= PRESS_MS then
     self.released.pressed = false
     self.released:invalidate()
     self.released = nil
@@ -484,7 +492,7 @@ function Screen:down(x, y)
   local target = self.root:hit(x, y)
   if not target then return end
   self.captured = target
-  self.pressedAt = sys.millis()
+  self.pressedAt = sys.getMillis()
   if target.press_style ~= false then
     target.pressed = true
     target:invalidate()
diff --git a/src/gfx/statusbar.h b/src/gfx/statusbar.h
deleted file mode 100644
index f8a2377..0000000
--- a/src/gfx/statusbar.h
+++ /dev/null
@@ -1,21 +0,0 @@
-#pragma once
-
-#include <TFT_eSPI.h>
-
-// Host-owned chrome across the top of the panel. Apps draw inside a viewport below it,
-// so nothing an app paints can reach the bar and every app's gui.height() shrinks by the
-// bar without the app knowing it exists. Both the painting and the height live in
-// /lib/statusbar.lua; the firmware only owns the clipping.
-namespace statusbar {
-
-constexpr int16_t DEFAULT_H = 22;  // when /lib/statusbar.lua declares no height
-
-// resetViewport() first: width()/height() report the *viewport* once one is set, so
-// re-applying over an existing viewport would shrink the app area again every time.
-// setRotation() leaves the old viewport metrics behind, so every rotation needs this too.
-inline void apply(TFT_eSPI& tft, int16_t barHeight) {
-  tft.resetViewport();
-  if (barHeight > 0) tft.setViewport(0, barHeight, tft.width(), tft.height() - barHeight, true);
-}
-
-}  // namespace statusbar
diff --git a/src/lua/bindings.h b/src/lua/bindings.h
index a4770b9..9f0ba9c 100644
--- a/src/lua/bindings.h
+++ b/src/lua/bindings.h
@@ -20,6 +20,7 @@ void bindApp(lua_State* L, LuaApp* owner);
 
 void registerGui(lua_State* L);
 void registerSys(lua_State* L);
+void registerSettings(lua_State* L);
 void registerInput(lua_State* L);
 void registerFs(lua_State* L);
 void registerWifi(lua_State* L);
diff --git a/src/lua/bindings/gui.cpp b/src/lua/bindings/gui.cpp
index 867534b..720cba6 100644
--- a/src/lua/bindings/gui.cpp
+++ b/src/lua/bindings/gui.cpp
@@ -124,13 +124,23 @@ static int l_gui_drawText(lua_State* L) {
   return 0;
 }
 
-// Only the current frame; sys.setRotation() is the persisted one.
+// Only the current frame; settings.setRotation() is the persisted one. Degrees, matching
+// settings: the 0-3 quarter turn index is TFT_eSPI's unit and stops at this boundary.
 static int l_gui_setRotation(lua_State* L) {
-  app(L)->tft.setRotation(luaL_checkinteger(L, 1));
+  lua_Integer degrees = luaL_checkinteger(L, 1);
+  luaL_argcheck(L, degrees % 90 == 0 && degrees >= 0 && degrees <= 270, 1, "0, 90, 180 or 270");
+  app(L)->tft.setRotation((degrees / 90) & 3);
   app(L)->applyViewport();
   return 0;
 }
 
+// The frame being drawn right now, which is not settings.getRotation(): an app may rotate
+// the panel transiently, and chrome has to follow the pixels rather than the preference.
+static int l_gui_getRotation(lua_State* L) {
+  lua_pushinteger(L, app(L)->tft.getRotation() * 90);
+  return 1;
+}
+
 // Escape hatch for an app that must reach the physical edges, like touch calibration:
 // the status bar and the viewport that keeps apps out of it both go away.
 static int l_gui_fullscreen(lua_State* L) {
@@ -149,13 +159,13 @@ void registerGui(lua_State* L) {
   static const luaL_Reg lib[] = {
       // --- Panel width in pixels, for the current rotation.
       // @return integer
-      {"width", l_gui_width},
+      {"getWidth", l_gui_width},
       // --- Hands the app the whole panel, hiding the status bar, until it is turned off.
       // @param on boolean
-      {"fullscreen", l_gui_fullscreen},
+      {"setFullscreen", l_gui_fullscreen},
       // --- Panel height in pixels, for the current rotation.
       // @return integer
-      {"height", l_gui_height},
+      {"getHeight", l_gui_height},
       // --- Fills the whole panel with one color.
       // @param color integer|nil Defaults to white.
       {"clear", l_gui_clear},
@@ -211,14 +221,17 @@ void registerGui(lua_State* L) {
       {"setTextSize", l_gui_setTextSize},
       // --- Height of the current font in pixels, at the current text size.
       // @return integer
-      {"fontHeight", l_gui_fontHeight},
+      {"getFontHeight", l_gui_fontHeight},
       // --- Width the given text would occupy in pixels.
       // @param text string
       // @return integer
-      {"textWidth", l_gui_textWidth},
-      // --- Rotates the frame for this draw only; sys.setRotation persists it.
-      // @param rotation integer 0 to 3, in quarter turns.
+      {"getTextWidth", l_gui_textWidth},
+      // --- Rotates the frame for this draw only; settings.setRotation persists it.
+      // @param degrees integer 0, 90, 180 or 270.
       {"setRotation", l_gui_setRotation},
+      // --- Rotation of the frame being drawn, which is not always the saved preference.
+      // @return integer Degrees clockwise.
+      {"getRotation", l_gui_getRotation},
       // --- Packs 8 bit channels into the panel's RGB565 color format.
       // @param r integer
       // @param g integer
diff --git a/src/lua/bindings/input.cpp b/src/lua/bindings/input.cpp
index db8757e..0540414 100644
--- a/src/lua/bindings/input.cpp
+++ b/src/lua/bindings/input.cpp
@@ -47,7 +47,7 @@ void registerInput(lua_State* L) {
       {"getRawTouch", l_input_getRawTouch},
       // --- Whether the panel is being touched.
       // @return boolean
-      {"touched", l_input_touched},
+      {"isTouched", l_input_touched},
       {nullptr, nullptr}};
   luaL_newlib(L, lib);
   lua_setglobal(L, "input");
diff --git a/src/lua/bindings/settings.cpp b/src/lua/bindings/settings.cpp
new file mode 100644
index 0000000..f7dbe50
--- /dev/null
+++ b/src/lua/bindings/settings.cpp
@@ -0,0 +1,111 @@
+// Persisted device preferences. The firmware is a first-class reader of these -- rotation
+// and calibration are needed before any Lua state exists, and on every touch after that --
+// so C++ owns the store and Lua reaches it through here rather than parsing the file.
+//
+// Every setter persists *and* applies its effect, so no caller has to remember a second
+// step. The one exception is the theme, whose palette lives in /lib/ui.lua and can only be
+// reloaded from Lua; ui.setTheme() is the seam that pairs the two.
+
+#include "../../net.h"
+#include "../../settings.h"
+#include "../bindings.h"
+#include "../lua_app.h"
+
+static int l_settings_getRotation(lua_State* L) {
+  lua_pushinteger(L, settings.rotation);
+  return 1;
+}
+
+// Persisted, unlike gui.setRotation() which only changes the current frame.
+static int l_settings_setRotation(lua_State* L) {
+  if (!settings.setRotation(luaL_checkinteger(L, 1))) {
+    lua_pushboolean(L, false);
+    return 1;
+  }
+  app(L)->tft.setRotation(settings.rotationIndex());
+  app(L)->applyViewport();
+  lua_pushboolean(L, settings.save());
+  return 1;
+}
+
+static int l_settings_getTheme(lua_State* L) {
+  lua_pushstring(L, settings.theme.c_str());
+  return 1;
+}
+
+// The firmware only stores the name; /lib/theme.lua decides what it looks like.
+static int l_settings_setTheme(lua_State* L) {
+  size_t length;
+  const char* name = luaL_checklstring(L, 1, &length);
+  if (!length || length > 32) {
+    lua_pushboolean(L, false);
+    return 1;
+  }
+  settings.theme = String(name, length);
+  lua_pushboolean(L, settings.save());
+  return 1;
+}
+
+static int l_settings_getTimezone(lua_State* L) {
+  lua_pushstring(L, settings.timezone.c_str());
+  return 1;
+}
+
+// Takes a POSIX TZ rule, not a zone name: /lib/timezones.lua is only a picker, so a
+// zone missing from that list is still reachable by writing the rule.
+static int l_settings_setTimezone(lua_State* L) {
+  size_t length;
+  const char* tz = luaL_checklstring(L, 1, &length);
+  if (!length || length > 48) {
+    lua_pushboolean(L, false);
+    return 1;
+  }
+  settings.timezone = String(tz, length);
+  net::applyTimezone();
+  lua_pushboolean(L, settings.save());
+  return 1;
+}
+
+static int l_settings_setCalibration(lua_State* L) {
+  settings.touchX0 = luaL_checkinteger(L, 1);
+  settings.touchY0 = luaL_checkinteger(L, 2);
+  settings.touchX1 = luaL_checkinteger(L, 3);
+  settings.touchY1 = luaL_checkinteger(L, 4);
+  lua_pushboolean(L, settings.save());
+  return 1;
+}
+
+void registerSettings(lua_State* L) {
+  static const luaL_Reg lib[] = {
+      // --- Saved screen rotation in degrees clockwise.
+      // @return integer
+      {"getRotation", l_settings_getRotation},
+      // --- Rotates the screen and saves it.
+      // @param degrees integer 0, 90, 180 or 270.
+      // @return boolean Whether the setting was saved.
+      {"setRotation", l_settings_setRotation},
+      // --- Name of the active theme in /lib/theme.lua.
+      // @return string
+      {"getTheme", l_settings_getTheme},
+      // --- Saves the theme name. Apps call ui.setTheme(), which also reloads the palette.
+      // @param name string
+      // @return boolean Whether the setting was saved.
+      {"setTheme", l_settings_setTheme},
+      // --- Active POSIX timezone rule.
+      // @return string
+      {"getTimezone", l_settings_getTimezone},
+      // --- Sets the timezone from a POSIX TZ rule and saves it.
+      // @param tz string For example EST5EDT,M3.2.0,M11.1.0.
+      // @return boolean Whether the setting was saved.
+      {"setTimezone", l_settings_setTimezone},
+      // --- Stores touch calibration, in the panel's unrotated frame.
+      // @param x0 integer Raw reading at the left edge.
+      // @param y0 integer Raw reading at the top edge.
+      // @param x1 integer Raw reading at the right edge.
+      // @param y1 integer Raw reading at the bottom edge.
+      // @return boolean Whether the setting was saved.
+      {"setCalibration", l_settings_setCalibration},
+      {nullptr, nullptr}};
+  luaL_newlib(L, lib);
+  lua_setglobal(L, "settings");
+}
diff --git a/src/lua/bindings/sys.cpp b/src/lua/bindings/sys.cpp
index 1aac526..d7a6454 100644
--- a/src/lua/bindings/sys.cpp
+++ b/src/lua/bindings/sys.cpp
@@ -1,7 +1,7 @@
-// Process control and persisted settings, plus the one-function `log` table.
+// Process control and runtime state, plus the one-function `log` table. Persisted
+// preferences live in the `settings` table, not here.
 
 #include "../../net.h"
-#include "../../settings.h"
 #include "../bindings.h"
 #include "../lua_app.h"
 
@@ -26,70 +26,6 @@ static int l_sys_launch(lua_State* L) {
   return 0;
 }
 
-static int l_sys_getRotation(lua_State* L) {
-  lua_pushinteger(L, settings.rotation);
-  return 1;
-}
-
-// Persisted, unlike gui.setRotation() which only changes the current frame.
-static int l_sys_setRotation(lua_State* L) {
-  if (!settings.setRotation(luaL_checkinteger(L, 1))) {
-    lua_pushboolean(L, false);
-    return 1;
-  }
-  app(L)->tft.setRotation(settings.rotationIndex());
-  app(L)->applyViewport();
-  lua_pushboolean(L, settings.save());
-  return 1;
-}
-
-static int l_sys_getTheme(lua_State* L) {
-  lua_pushstring(L, settings.theme.c_str());
-  return 1;
-}
-
-// The firmware only stores the name; /lib/theme.lua decides what it looks like.
-static int l_sys_setTheme(lua_State* L) {
-  size_t length;
-  const char* name = luaL_checklstring(L, 1, &length);
-  if (!length || length > 32) {
-    lua_pushboolean(L, false);
-    return 1;
-  }
-  settings.theme = String(name, length);
-  lua_pushboolean(L, settings.save());
-  return 1;
-}
-
-static int l_sys_getTimezone(lua_State* L) {
-  lua_pushstring(L, settings.timezone.c_str());
-  return 1;
-}
-
-// Takes a POSIX TZ rule, not a zone name: /lib/timezones.lua is only a picker, so a
-// zone missing from that list is still reachable by writing the rule.
-static int l_sys_setTimezone(lua_State* L) {
-  size_t length;
-  const char* tz = luaL_checklstring(L, 1, &length);
-  if (!length || length > 48) {
-    lua_pushboolean(L, false);
-    return 1;
-  }
-  settings.timezone = String(tz, length);
-  net::applyTimezone();
-  lua_pushboolean(L, settings.save());
-  return 1;
-}
-
-static int l_sys_setCalibration(lua_State* L) {
-  settings.touchX0 = luaL_checkinteger(L, 1);
-  settings.touchY0 = luaL_checkinteger(L, 2);
-  settings.touchX1 = luaL_checkinteger(L, 3);
-  settings.touchY1 = luaL_checkinteger(L, 4);
-  lua_pushboolean(L, settings.save());
-  return 1;
-}
-
 // Lua's os.time()/os.date() work off the same system clock, so this is the only
 // binding a clock UI needs: it says whether that clock means anything yet.
 static int l_sys_clockSynced(lua_State* L) {
@@ -97,6 +33,12 @@ static int l_sys_clockSynced(lua_State* L) {
   return 1;
 }
 
+static int l_sys_memory(lua_State* L) {
+  lua_pushinteger(L, ESP.getFreeHeap());
+  lua_pushinteger(L, ESP.getHeapSize());
+  return 2;
+}
+
 static int logAt(lua_State* L, const char* level) {
   Serial.printf("[lua:%s] %s\n", level, luaL_checkstring(L, 1));
   return 0;
@@ -137,7 +79,7 @@ void registerSys(lua_State* L) {
   static const luaL_Reg lib[] = {
       // --- Milliseconds since boot.
       // @return integer
-      {"millis", l_sys_millis},
+      {"getMillis", l_sys_millis},
       // --- Blocks for the given time.
       // @param ms integer
       {"delay", l_sys_delay},
@@ -145,44 +87,20 @@ void registerSys(lua_State* L) {
       {"exit", l_sys_exit},
       // --- Directory name of the running app, for example "settings".
       // @return string
-      {"appName", l_sys_appName},
+      {"getAppName", l_sys_appName},
       // --- Sets how often on_tick() runs. Errors when on_tick is not defined.
       // @param intervalMs integer 0 stops ticking; anything else is clamped to 33..3600000.
       {"setTickInterval", l_sys_setTickInterval},
       // --- Ends this app and starts another one.
       // @param path string Absolute path to the app's main.lua.
       {"launch", l_sys_launch},
-      // --- Saved screen rotation in degrees clockwise.
-      // @return integer
-      {"getRotation", l_sys_getRotation},
-      // --- Rotates the screen and saves it.
-      // @param degrees integer 0, 90, 180 or 270.
-      // @return boolean Whether the setting was saved.
-      {"setRotation", l_sys_setRotation},
-      // --- Name of the active theme in /lib/theme.lua.
-      // @return string
-      {"getTheme", l_sys_getTheme},
-      // --- Selects a theme by name and saves it.
-      // @param name string
-      // @return boolean Whether the setting was saved.
-      {"setTheme", l_sys_setTheme},
-      // --- Stores touch calibration, in the panel's unrotated frame.
-      // @param x0 integer Raw reading at the left edge.
-      // @param y0 integer Raw reading at the top edge.
-      // @param x1 integer Raw reading at the right edge.
-      // @param y1 integer Raw reading at the bottom edge.
-      // @return boolean Whether the setting was saved.
-      {"setCalibration", l_sys_setCalibration},
+      // --- Free and total heap, in bytes.
+      // @return integer Free bytes.
+      // @return integer Total bytes.
+      {"getMemory", l_sys_memory},
       // --- Whether SNTP has answered. Until it has, os.time() is only a build-time floor.
       // @return boolean
-      {"clockSynced", l_sys_clockSynced},
-      // --- Active POSIX timezone rule.
-      // @return string
-      {"getTimezone", l_sys_getTimezone},
-      // --- Sets the timezone from a POSIX TZ rule and saves it.
-      // @param tz string For example EST5EDT,M3.2.0,M11.1.0.
-      // @return boolean Whether the setting was saved.
-      {"setTimezone", l_sys_setTimezone},
+      {"isClockSynced", l_sys_clockSynced},
       {nullptr, nullptr}};
   luaL_newlib(L, lib);
   lua_setglobal(L, "sys");
diff --git a/src/lua/bindings/wifi.cpp b/src/lua/bindings/wifi.cpp
index 4b7bfdf..16fb336 100644
--- a/src/lua/bindings/wifi.cpp
+++ b/src/lua/bindings/wifi.cpp
@@ -124,13 +124,13 @@ void registerWifi(lua_State* L) {
       // --- Current connection state.
       // @return table Fields state, ssid, ip and rssi. state is one of disconnected,
       // --- connecting, connected, not_found or failed.
-      {"status", l_wifi_status},
+      {"getStatus", l_wifi_status},
       // --- Whether the station is associated.
       // @return boolean
       {"isConnected", l_wifi_isConnected},
       // --- Current IPv4 address.
       // @return string The address, or 0.0.0.0 when not connected.
-      {"localIP", l_wifi_localIP},
+      {"getLocalIP", l_wifi_localIP},
       // --- Drops the connection but keeps the saved credentials.
       {"disconnect", l_wifi_disconnect},
       // --- Drops the connection and erases the saved credentials.
diff --git a/src/lua/lua_app.cpp b/src/lua/lua_app.cpp
index d480808..96a449f 100644
--- a/src/lua/lua_app.cpp
+++ b/src/lua/lua_app.cpp
@@ -5,7 +5,6 @@
 
 #include <algorithm>
 
-#include "../gfx/statusbar.h"
 #include "../settings.h"
 #include "bindings.h"
 
@@ -46,7 +45,14 @@ void LuaApp::mapTouch(const TS_Point& p, int16_t& x, int16_t& y) const {
   y -= barInset();
 }
 
-void LuaApp::applyViewport() { statusbar::apply(tft, barInset()); }
+// resetViewport() first: width()/height() report the *viewport* once one is set, so
+// re-applying over an existing one would shrink the app area again every time.
+// setRotation() leaves the old viewport metrics behind, so every rotation needs this too.
+void LuaApp::applyViewport() {
+  int16_t inset = barInset();
+  tft.resetViewport();
+  if (inset > 0) tft.setViewport(0, inset, tft.width(), tft.height() - inset, true);
+}
 
 void LuaApp::setFullscreen(bool on) {
   fullscreen = on;
@@ -127,6 +133,9 @@ bool LuaApp::load(const char* path, bool isHome) {
   // gui.height() at the top of init() has to see the area it actually owns.
   loadStatusBar();
   applyViewport();
+  // Painted before the app's chunk runs, not on the next bar tick: loading a script off
+  // the SD card takes long enough that the previous app's name would linger visibly.
+  if (barInset() > 0 && !barBroken) drawStatusBar();
 
   if (loadScript(state, path) != LUA_OK) {
     fail(lua_tostring(state, -1));
@@ -157,17 +166,20 @@ static lua_Integer barField(lua_State* L, const char* key, lua_Integer fallback)
 // app, and there is only one of those per state.
 void LuaApp::loadStatusBar() {
   barBroken = false;
-  barHeight = statusbar::DEFAULT_H;
+  barHeight = DEFAULT_BAR_H;
   barIntervalMs = BAR_INTERVAL_MS;
   lua_getglobal(state, "require");
   lua_pushstring(state, "statusbar");
   if (lua_pcall(state, 1, 1, 0) != LUA_OK || !lua_istable(state, -1)) {
     Serial.printf("[statusbar] unavailable: %s\n", luaL_tolstring(state, -1, nullptr));
+    // Nothing has measured the panel yet, so surrendering the strip here is free. A bar
+    // that dies later keeps its rows, because the app has already laid itself out.
     barBroken = true;
+    barHeight = 0;
     lua_pop(state, 2);
     return;
   }
-  barHeight = barField(state, "height", statusbar::DEFAULT_H);
+  barHeight = barField(state, "height", DEFAULT_BAR_H);
   barIntervalMs = std::max((lua_Integer)MIN_TICK_MS, barField(state, "interval", BAR_INTERVAL_MS));
   lua_setglobal(state, "__statusbar");
   nextBarMs = 0;
@@ -197,6 +209,7 @@ void LuaApp::setTickInterval(uint32_t intervalMs) {
 void LuaApp::registerBindings() {
   registerGui(state);
   registerSys(state);
+  registerSettings(state);
   registerInput(state);
   registerFs(state);
   registerWifi(state);
@@ -273,7 +286,7 @@ void LuaApp::loop() {
     if (!running()) return;
   }
 
-  if (barInset() > 0 && now >= nextBarMs) {
+  if (barInset() > 0 && !barBroken && now >= nextBarMs) {
     nextBarMs = now + barIntervalMs;
     drawStatusBar();
   }
diff --git a/src/lua/lua_app.h b/src/lua/lua_app.h
index cca914d..9590dd9 100644
--- a/src/lua/lua_app.h
+++ b/src/lua/lua_app.h
@@ -69,7 +69,8 @@ class LuaApp {
   bool homeArmed = false;
   String appName;
   // One strike: a bar that failed once fails identically every second, and the serial
-  // log is the only place anyone would see it.
+  // log is the only place anyone would see it. The strip stays reserved either way, so a
+  // bar that dies mid-run never resizes the app underneath it.
   bool barBroken = false;
   int16_t barHeight = 0;
   uint32_t nextBarMs = 0;
@@ -88,12 +89,13 @@ class LuaApp {
   uint32_t nextDrawMs = 0;
 
   static constexpr uint32_t DRAW_INTERVAL_MS = 33;
-  // Default only: /lib/statusbar.lua overrides it with an `interval` field.
+  // Defaults only: /lib/statusbar.lua overrides both with `interval` and `height` fields.
   static constexpr uint32_t BAR_INTERVAL_MS = 1000;
+  static constexpr int16_t DEFAULT_BAR_H = 22;
 
   // Zero whenever the app owns the panel, so one accessor answers both the viewport
   // and the touch offset.
-  int16_t barInset() const { return (fullscreen || barBroken) ? 0 : barHeight; }
+  int16_t barInset() const { return fullscreen ? 0 : barHeight; }
 
   // The home button is the leading square of the bar, which is what /lib/statusbar.lua
   // paints into. Touches are in app space, so the bar is above y = 0.
diff --git a/src/main.cpp b/src/main.cpp
index b4dbb27..06662b8 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4,7 +4,6 @@
 #include <WiFi.h>
 #include <XPT2046_Touchscreen.h>
 
-#include "gfx/statusbar.h"
 #include "lua/lua_app.h"
 #include "net.h"
 #include "settings.h"
@@ -50,7 +49,7 @@ void fallbackScreen(const char* message) {
 void startApp(const String& path) {
   // Full panel until the app's own status bar module reports its height in load().
   tft.setRotation(settings.rotationIndex());  // apps may have rotated the frame
-  statusbar::apply(tft, 0);
+  tft.resetViewport();  // load() re-clips once the new app's bar reports its height
   Serial.printf("launching %s\n", path.c_str());
   if (app.load(path.c_str(), path == HOME)) return;
   if (path == HOME) fallbackScreen("home failed to start");
diff --git a/stubs/slate32.lua b/stubs/slate32.lua
index 710c98e..a4d1c63 100644
--- a/stubs/slate32.lua
+++ b/stubs/slate32.lua
@@ -38,15 +38,15 @@ gui = {}
 
 --- Panel width in pixels, for the current rotation.
 ---@return integer
-function gui.width() end
+function gui.getWidth() end
 
 --- Hands the app the whole panel, hiding the status bar, until it is turned off.
 ---@param on boolean
-function gui.fullscreen(on) end
+function gui.setFullscreen(on) end
 
 --- Panel height in pixels, for the current rotation.
 ---@return integer
-function gui.height() end
+function gui.getHeight() end
 
 --- Fills the whole panel with one color.
 ---@param color integer? Defaults to white.
@@ -111,16 +111,20 @@ function gui.setTextSize(size) end
 
 --- Height of the current font in pixels, at the current text size.
 ---@return integer
-function gui.fontHeight() end
+function gui.getFontHeight() end
 
 --- Width the given text would occupy in pixels.
 ---@param text string
 ---@return integer
-function gui.textWidth(text) end
+function gui.getTextWidth(text) end
 
---- Rotates the frame for this draw only; sys.setRotation persists it.
----@param rotation integer 0 to 3, in quarter turns.
-function gui.setRotation(rotation) end
+--- Rotates the frame for this draw only; settings.setRotation persists it.
+---@param degrees integer 0, 90, 180 or 270.
+function gui.setRotation(degrees) end
+
+--- Rotation of the frame being drawn, which is not always the saved preference.
+---@return integer Degrees clockwise.
+function gui.getRotation() end
 
 --- Packs 8 bit channels into the panel's RGB565 color format.
 ---@param r integer
@@ -197,7 +201,7 @@ function input.getRawTouch() end
 
 --- Whether the panel is being touched.
 ---@return boolean
-function input.touched() end
+function input.isTouched() end
 
 ---@class loglib
 log = {}
@@ -214,12 +218,50 @@ function log.info(message) end
 ---@param message string
 function log.error(message) end
 
+---@class settingslib
+settings = {}
+
+--- Saved screen rotation in degrees clockwise.
+---@return integer
+function settings.getRotation() end
+
+--- Rotates the screen and saves it.
+---@param degrees integer 0, 90, 180 or 270.
+---@return boolean Whether the setting was saved.
+function settings.setRotation(degrees) end
+
+--- Name of the active theme in /lib/theme.lua.
+---@return string
+function settings.getTheme() end
+
+--- Saves the theme name. Apps call ui.setTheme(), which also reloads the palette.
+---@param name string
+---@return boolean Whether the setting was saved.
+function settings.setTheme(name) end
+
+--- Active POSIX timezone rule.
+---@return string
+function settings.getTimezone() end
+
+--- Sets the timezone from a POSIX TZ rule and saves it.
+---@param tz string For example EST5EDT,M3.2.0,M11.1.0.
+---@return boolean Whether the setting was saved.
+function settings.setTimezone(tz) end
+
+--- Stores touch calibration, in the panel's unrotated frame.
+---@param x0 integer Raw reading at the left edge.
+---@param y0 integer Raw reading at the top edge.
+---@param x1 integer Raw reading at the right edge.
+---@param y1 integer Raw reading at the bottom edge.
+---@return boolean Whether the setting was saved.
+function settings.setCalibration(x0, y0, x1, y1) end
+
 ---@class syslib
 sys = {}
 
 --- Milliseconds since boot.
 ---@return integer
-function sys.millis() end
+function sys.getMillis() end
 
 --- Blocks for the given time.
 ---@param ms integer
@@ -230,7 +272,7 @@ function sys.exit() end
 
 --- Directory name of the running app, for example "settings".
 ---@return string
-function sys.appName() end
+function sys.getAppName() end
 
 --- Sets how often on_tick() runs. Errors when on_tick is not defined.
 ---@param intervalMs integer 0 stops ticking; anything else is clamped to 33..3600000.
@@ -240,44 +282,14 @@ function sys.setTickInterval(intervalMs) end
 ---@param path string Absolute path to the app's main.lua.
 function sys.launch(path) end
 
---- Saved screen rotation in degrees clockwise.
----@return integer
-function sys.getRotation() end
-
---- Rotates the screen and saves it.
----@param degrees integer 0, 90, 180 or 270.
----@return boolean Whether the setting was saved.
-function sys.setRotation(degrees) end
-
---- Name of the active theme in /lib/theme.lua.
----@return string
-function sys.getTheme() end
-
---- Selects a theme by name and saves it.
----@param name string
----@return boolean Whether the setting was saved.
-function sys.setTheme(name) end
-
---- Stores touch calibration, in the panel's unrotated frame.
----@param x0 integer Raw reading at the left edge.
----@param y0 integer Raw reading at the top edge.
----@param x1 integer Raw reading at the right edge.
----@param y1 integer Raw reading at the bottom edge.
----@return boolean Whether the setting was saved.
-function sys.setCalibration(x0, y0, x1, y1) end
+--- Free and total heap, in bytes.
+---@return integer Free bytes.
+---@return integer Total bytes.
+function sys.getMemory() end
 
 --- Whether SNTP has answered. Until it has, os.time() is only a build-time floor.
 ---@return boolean
-function sys.clockSynced() end
-
---- Active POSIX timezone rule.
----@return string
-function sys.getTimezone() end
-
---- Sets the timezone from a POSIX TZ rule and saves it.
----@param tz string For example EST5EDT,M3.2.0,M11.1.0.
----@return boolean Whether the setting was saved.
-function sys.setTimezone(tz) end
+function sys.isClockSynced() end
 
 ---@class wifilib
 wifi = {}
@@ -295,7 +307,7 @@ function wifi.connect(ssid, password) end
 --- Current connection state.
 --- connecting, connected, not_found or failed.
 ---@return table Fields state, ssid, ip and rssi. state is one of disconnected,
-function wifi.status() end
+function wifi.getStatus() end
 
 --- Whether the station is associated.
 ---@return boolean
@@ -303,7 +315,7 @@ function wifi.isConnected() end
 
 --- Current IPv4 address.
 ---@return string The address, or 0.0.0.0 when not connected.
-function wifi.localIP() end
+function wifi.getLocalIP() end
 
 --- Drops the connection but keeps the saved credentials.
 function wifi.disconnect() end
diff --git a/test/fake_device.lua b/test/fake_device.lua
index 1ebec47..e823e45 100644
--- a/test/fake_device.lua
+++ b/test/fake_device.lua
@@ -22,7 +22,9 @@ local device = {
   networks = {},      -- what wifi.scan() returns
   status = {state = "disconnected", ssid = "", ip = "", rssi = 0},
   painted = {},       -- every drawText call, in order
-  calibration = nil,  -- last sys.setCalibration()
+  calibration = nil,  -- last settings.setCalibration()
+  freeHeap = 200000,
+  totalHeap = 320000,
   connected = nil,    -- last wifi.connect()
   exited = false,
   launched = nil,
@@ -39,8 +41,8 @@ function device.install()
   gui = {
     color = function(r, g, b) return r * 65536 + g * 256 + b end,
     -- Rotation swaps the frame, exactly as TFT_eSPI reports it.
-    width = function() return device.rotation % 180 == 0 and 320 or 480 end,
-    height = function() return device.rotation % 180 == 0 and 480 or 320 end,
+    getWidth = function() return device.rotation % 180 == 0 and 320 or 480 end,
+    getHeight = function() return device.rotation % 180 == 0 and 480 or 320 end,
     clear = function() end,
     fillRect = function() end,
     drawRect = function() end,
@@ -51,21 +53,27 @@ function device.install()
       device.painted[#device.painted + 1] = {label = label, x = x, y = y}
     end,
     setTextSize = function(size) device.textSize = size end,
-    fontHeight = function() return device.fontHeight * device.textSize end,
-    textWidth = function(text) return #text * device.charWidth * device.textSize end,
-    setRotation = function() end,
-    fullscreen = function(on) device.fullscreen = on and true or false end,
+    getFontHeight = function() return device.fontHeight * device.textSize end,
+    getTextWidth = function(text) return #text * device.charWidth * device.textSize end,
+    setRotation = function(degrees) device.rotation = degrees end,
+    getRotation = function() return device.rotation end,
+    setFullscreen = function(on) device.fullscreen = on and true or false end,
   }
 
   sys = {
-    millis = function() return device.now end,
+    getMillis = function() return device.now end,
     exit = function() device.exited = true end,
-    appName = function() return device.appName end,
+    getAppName = function() return device.appName end,
+    getMemory = function() return device.freeHeap, device.totalHeap end,
+    isClockSynced = function() return device.clockSynced end,
     setTickInterval = function(ms)
       assert(ms == 0 or on_tick, "setTickInterval without on_tick")
       device.tickInterval = ms
     end,
     launch = function(path) device.launched = path end,
+  }
+
+  settings = {
     getRotation = function() return device.rotation end,
     setRotation = function(degrees)
       if degrees % 90 ~= 0 or degrees < 0 or degrees > 270 then return false end
@@ -75,13 +83,12 @@ function device.install()
     getTheme = function() return device.theme end,
     setTheme = function(name) device.theme = name return saved() end,
     setCalibration = function(...) device.calibration = {...} return saved() end,
-    clockSynced = function() return device.clockSynced end,
     getTimezone = function() return device.timezone end,
     setTimezone = function(tz) device.timezone = tz return saved() end,
   }
 
   input = {
-    touched = function() return device.raw ~= nil end,
+    isTouched = function() return device.raw ~= nil end,
     getTouch = function()
       if not device.raw then return nil end
       return device.raw[1], device.raw[2]
@@ -102,7 +109,7 @@ function device.install()
 
   wifi = {
     scan = function() return device.networks end,
-    status = function() return device.status end,
+    getStatus = function() return device.status end,
     connect = function(ssid, password)
       device.connected = {ssid, password}
       return saved()
diff --git a/test/settings_calibration.lua b/test/settings_calibration.lua
index f0fa2a7..3ff2e9e 100644
--- a/test/settings_calibration.lua
+++ b/test/settings_calibration.lua
@@ -56,15 +56,15 @@ assert(fx0 > fx1, "flipped axis should descend")
 local zones = require("timezones")
 init()
 tapRow("timezone")
-assert(sys.getTimezone() == zones[2].tz, "timezone " .. sys.getTimezone())
+assert(settings.getTimezone() == zones[2].tz, "timezone " .. settings.getTimezone())
 tapRow("timezone")
-assert(sys.getTimezone() == zones[3].tz, "timezone " .. sys.getTimezone())
+assert(settings.getTimezone() == zones[3].tz, "timezone " .. settings.getTimezone())
 
 -- Rotation cycles through the four quarter turns and wraps back to 0.
 init()
 for _, expected in ipairs({90, 180, 270, 0}) do
   tapRow("rotation")
-  assert(sys.getRotation() == expected, "rotation " .. sys.getRotation())
+  assert(settings.getRotation() == expected, "rotation " .. settings.getRotation())
 end
 
 -- Calibration collects one sample per target and saves on the second release.
diff --git a/test/statusbar_dirty.lua b/test/statusbar_dirty.lua
new file mode 100644
index 0000000..f5694c1
--- /dev/null
+++ b/test/statusbar_dirty.lua
@@ -0,0 +1,59 @@
+-- Run: lua test/statusbar_dirty.lua
+-- Asserts the bar repaints only what changed, and that it notices the two things it can
+-- only learn by looking: rotation and theme. The clock is pinned unsynced so its text is
+-- constant and every other field can be steered on its own.
+package.path = "sdcard/lib/?.lua;test/?.lua;" .. package.path
+
+local device = require("fake_device").install()
+local ui = require("ui")
+local statusbar = require("statusbar")
+
+device.clockSynced = false
+
+-- Returns the labels drawn by one draw() call.
+local function paint()
+  device.painted = {}
+  statusbar.draw(true)
+  local labels = {}
+  for _, entry in ipairs(device.painted) do labels[#labels + 1] = entry.label end
+  return labels
+end
+
+local function has(labels, want)
+  for _, label in ipairs(labels) do if label == want then return true end end
+  return false
+end
+
+local first = paint()
+assert(has(first, device.appName), "first draw paints the app name")
+assert(has(first, "--:--:--"), "first draw paints the clock")
+
+assert(#paint() == 0, "an unchanged bar paints nothing")
+
+device.freeHeap = device.freeHeap - 32000
+local memOnly = paint()
+assert(#memOnly == 1 and memOnly[1]:find("%%"), "only the memory slot repaints")
+
+device.status = {state = "connected", ssid = "x", ip = "", rssi = -50}
+assert(#paint() == 0, "signal bars are not text, so nothing is drawn")
+device.status = {state = "disconnected", ssid = "", ip = "", rssi = 0}
+
+-- Rotation and theme invalidate everything, because every slot moves or recolors.
+device.rotation = 180
+assert(has(paint(), device.appName), "rotation repaints the whole bar")
+assert(#paint() == 0, "and settles again afterwards")
+
+device.theme = "dark"
+ui.reloadTheme()
+assert(has(paint(), device.appName), "a theme change repaints the whole bar")
+
+-- Leaving fullscreen is the one change draw() cannot see: the app painted over the bar
+-- while nothing about the bar's own state moved.
+device.theme = "light"
+ui.reloadTheme()
+paint()
+statusbar.setFullscreen(true)
+statusbar.setFullscreen(false)
+assert(has(paint(), device.appName), "leaving fullscreen repaints the whole bar")
+
+print("ok")