% app-size-and-energy.tex — app thinning (slicing, ODR, bitcode gone), the three sizes,
% measuring size; energy: tail energy, batching, discretionary URLSession, location,
% Low Power Mode, thermal state, MetricKit, Instruments.
% Sources: docs/memos/ios-app-thinning-ondemand.md, docs/memos/ios-energy-efficiency.md
% (checked against docs/school/notes/knowledge-gaps-2026-09-23.md).
% Not used from the sources: the "cellular cap configurable by entitlement" claim
% (thinning Q9) and "background sessions are discretionary by default" (energy Q4).
% Build ONLY with: tools/print/print-sheet.py <this>.tex --dry-run
% @source: hiot monorepo, docs/school/sheets/ios-platform/app-size-and-energy.tex — the SOURCE OF TRUTH; a copy anywhere else (e.g. artur.gurgul.pro) is regenerated from it, never edited
% @labels: area=ios-platform kind=concept level=senior platform=ios new=no round=missing-2026-09-25 topic=performance,build
% @tags: app-thinning, slicing, on-demand-resources, nsbundleresourcerequest, bitcode, app-size, radio-tail-energy, batching, isdiscretionary, low-power-mode, thermalstate, metrickit
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\begin{document}

\sheettitle{App size \& energy — thinning, ODR, what drains the battery}{ios-platform · memo}

\oneliner{\textbf{Size}: the App Store \emph{slices} one universal upload into
per-device variants, \textbf{On-Demand Resources} move optional content out of the
download, bitcode is \textbf{gone}. \textbf{Energy}: do \emph{less} work, \emph{less
often}, in \emph{bigger batches}, woken by events not timers, at the lowest fidelity
the user accepts — the radio \textbf{tail}, GPS and wakeups cost more than bytes.}

\vspace{3pt}
\noindent\begin{tikzpicture}[sheet]
  % ── left: thinning ──
  \node[font=\bfseries\small, anchor=west] at (-0.1,3.2) {one upload $\to$ per-device downloads};
  \node[sb, minimum width=21mm, minimum height=15mm] (up) at (1.0,1.55) {\textbf{upload}\\universal \texttt{.ipa}\\all archs, @2x+@3x,\\all GPU variants};
  \node[var] (v1) at (4.3,2.55) {iPhone, @3x};
  \node[var] (v2) at (4.3,1.85) {iPhone, @2x};
  \node[var] (v3) at (4.3,1.15) {iPad, @2x, GPU 4};
  \node[lbl] at (4.3,0.62) {… one per device trait set};
  \foreach \v in {v1,v2,v3} \draw[flow] (up.east) -- (\v.west);
  \node[lbl, text=sheetGreen!60!black] at (2.6,0.8) {App Store\\\textbf{slicing}};
  \node[sb, minimum width=15mm] (ph) at (7.1,2.55) {device};
  \draw[hot] (v1) -- node[lbl, above]{download} node[lbl, below]{(compressed)} (ph);
  \node[lbl, anchor=south] at (7.1,2.85) {\textbf{install} size = unpacked};
  \node[odr] (t) at (4.3,-0.05) {ODR tags on Apple CDN};
  \draw[hot, dashed] (t.east) -| node[lbl, right, pos=0.75, align=left]{on\\demand} (ph.south);
  \node[lbl, anchor=west] at (-0.1,-0.55) {cellular: \textbf{download} size vs the 200 MB prompt · loose files in Copy Bundle Resources ship to \emph{every} variant};
  \draw[sheetGrey!40] (8.55,3.35) -- (8.55,-0.75);
  % ── right: radio tail energy ──
  \node[font=\bfseries\small, anchor=west] at (8.7,3.2) {radio tail: same 4 requests, spread vs batched};
  % spread
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  \node[lbl, text=sheetGreen!60!black, anchor=west] at (11.7,0.75) {one tail, then the radio \textbf{sleeps}};
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  \fill[sheetOrange!35] (10.3,-0.15) rectangle ++(0.2,0.2); \node[lbl, anchor=west] at (10.55,-0.05) {tail: radio stays up seconds after the last byte (cellular $>$ Wi-Fi)};
  \node[lbl, anchor=west] at (8.7,-0.55) {bytes are cheap; \emph{waking} the radio is not — the tail dominates small requests};
\end{tikzpicture}

\begin{multicols}{2}

\section{App size — how it works}
\begin{itemize}
  \item \textbf{Slicing} — a variant per device: arch + asset-catalog traits (scale,
        idiom, Metal GPU family, memory class). Only \textbf{asset catalogs} slice.
  \item \textbf{Bitcode} — deprecated in Xcode 14; the App Store no longer takes it.
  \item \textbf{Three sizes} — \emph{upload} (universal) · \emph{download} (compressed
        variant; the cellular prompt checks it) · \emph{install} (unpacked). Over cellular
        iOS asks above \textbf{200 MB} (iOS 13+; user-adjustable in Settings).
  \item \textbf{ODR} — tagged resources hosted by the App Store: \emph{initial install},
        \emph{prefetched} (after install), \emph{on demand}.
        \texttt{NSBundleResourceRequest(tags:)} + \texttt{beginAccessingResources}; the
        \textbf{live request} pins them — after \texttt{endAccessingResources}/deinit they
        are purgeable. Own CDN: \textbf{Background Assets} (iOS 16).
  \item \textbf{Measure} — Organizer export, \emph{App Thinning: all variants} $\to$
        \texttt{App Thinning Size Report.txt} (per variant, compressed + not); App Store
        Connect file sizes; \texttt{assetutil} on \texttt{Assets.car}.
  \item \textbf{Shrink} — catalog assets (HEIC, vectors), drop unused
        images/localizations; \texttt{-Osize}, dead-code stripping, symbols into the
        dSYM, fewer dynamic frameworks.
\end{itemize}

\section{Energy — what drains}
\begin{itemize}
  \item \textbf{Radio tail} (diagram) — every wake of cellular/Wi-Fi pays seconds of
        high power. Polling every 10 s = the radio never sleeps; push (APNs rides one
        shared system connection) = the OS pays.
  \item \textbf{CPU wakeups} — timers, polling loops, chatty background work stop deep
        idle. \texttt{timer.tolerance} $\geq$ 10\% lets iOS coalesce. Off-main $\neq$
        cheaper: same joules.
  \item \textbf{GPS} — continuous \texttt{kCLLocationAccuracyBest} is among the worst.
        Least accuracy you need, \texttt{distanceFilter}, one-shot
        \texttt{requestLocation()}, significant-change ($\sim$500 m, $\geq$ 5 min) or region
        monitoring, \textbf{stop} when the screen closes. ``When In Use'' can still drain:
        mode + accuracy decide, not the permission.
  \item \textbf{Display + GPU} — \texttt{isIdleTimerDisabled} left on, needless 120 Hz
        animation, offscreen passes.
\end{itemize}

\section{Energy — what to do}
\begin{itemize}
  \item \textbf{Batch} — buffer analytics, prefetch in one burst, flush on
        Wi-Fi/charging. \texttt{isDiscretionary = true}: iOS picks the moment (automatic
        for transfers started in the background). Respect Low Data Mode
        (\texttt{allowsConstrainedNetworkAccess}).
  \item \textbf{Low Power Mode} — pause prefetch, autoplay, decoration; never break what
        the user just asked for. Read
        \texttt{ProcessInfo.processInfo.isLowPowerModeEnabled}, observe
        \texttt{NSProcessInfoPowerStateDidChange}.
  \item \textbf{Thermal} — \texttt{thermalState} \texttt{.nominal}/\texttt{.fair}/\texttt{.serious}/\texttt{.critical}:
        at \texttt{.serious} cut frame rate, quality, effects.
  \item \textbf{Measure} — Xcode \emph{Energy Impact} gauge; Instruments \textbf{Energy
        Log} (on device); field: \textbf{MetricKit} (iOS 13) \texttt{MXMetricPayload}
        $\sim$daily — \texttt{cpuMetrics}, \texttt{locationActivityMetrics},
        \texttt{networkTransferMetrics}, \texttt{cellularConditionMetrics},
        \texttt{MXCPUExceptionDiagnostic}; Organizer $\to$ Energy.
\end{itemize}

\section{Example}
\begin{lstlisting}[language=SwiftSheet]
let req = NSBundleResourceRequest(tags: ["level-3"])
req.beginAccessingResources { error in // keep `req` alive
  if let error { return showRetry(error) }
  loadLevel3() }            // later: req.endAccessingResources()
let cfg = URLSessionConfiguration
  .background(withIdentifier: "sync")
cfg.isDiscretionary = true             // iOS picks the moment
cfg.allowsExpensiveNetworkAccess = false // no cellular
let pi = ProcessInfo.processInfo
if pi.isLowPowerModeEnabled
   || [.serious, .critical].contains(pi.thermalState) {
  prefetcher.pause() }                 // shed optional work
\end{lstlisting}

\section{Interview traps}
\begin{itemize}
  \trap{``Enable bitcode for thinning'' — removed; slicing + ODR remain.}
  \trap{ODR read by bundle path without a live request — maybe never downloaded, or
        purged. ODR moves \emph{when} bytes arrive: loading UI, retry, offline.}
  \trap{``One small request can't matter'' — tail energy. Batch it.}
\end{itemize}

\section{Remember}
\textbf{Slice, tag, strip. Batch, defer, coarsen, stop.}

\section{Likely questions}
\begin{enumerate}
  \item Download vs install size? — compressed variant vs unpacked.
  \item Keep ODR from purging? — hold the request object.
  \item Real-user energy data? — MetricKit, Organizer.
\end{enumerate}

\end{multicols}

\noindent{\footnotesize\color{sheetGrey}\textit{Related:} background execution ·
push notifications · linking \& launch time · instruments \& performance · rendering
pipeline · crashes \& MetricKit}

\end{document}