226 lines
8.5 KiB
Markdown
226 lines
8.5 KiB
Markdown
# rspektrum
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**rspektrum** is an interactive spectrogram viewer for inspecting radio captures
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and arbitrary audio. It loads a WAV file, computes a short-time Fourier transform
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(STFT), and draws the result as a zoomable, pannable time–frequency image. Its
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distinguishing feature is support for **mLnL annotations** — labelled regions
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(TX frames, assertion outcomes, impairment fires, …) carried *inside* the WAV
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file itself — which it overlays on the measured spectrogram so you can compare
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what a modem *intended* to transmit against what actually hit the air.
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You can box a time/frequency region, hear it back through a bandpass filter, and
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export either the picture (PNG) or the isolated audio (WAV). rspektrum runs three
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ways: a native desktop app (C + raylib), a headless command-line renderer, and a
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WebAssembly build in the browser.
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## [Click for Video Demo](https://nicecrew.tv/w/2w9Y5qvKuDz6mwrzAweryW)
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---
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## What it's for
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The primary use case is reviewing captures from the **mLink** radio stack: a WAV
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recording of an over-the-air signal with an embedded `mLnL` chunk describing what
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the modem/daemon believed it was transmitting at each instant. rspektrum renders
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those annotations on top of the measured spectrogram, frame by frame, so intent
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and reality sit side by side.
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It also works as a general-purpose spectrogram tool for plain WAVs with no
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annotations. See [`mlnl_chunk_spec.md`](mlnl_chunk_spec.md) for the annotation
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format.
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---
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## Features
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- **STFT spectrogram** — selectable colormaps, adjustable dB floor / dynamic
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range, absolute (dBFS) or relative amplitude scaling.
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- **mLnL annotation overlay** — labelled boxes from the WAV's embedded annotation
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chunk; hover a box (or its region on the scope) for per-frame detail (sequence,
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channel, rate, scheduling offset…).
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- **Zoom & pan** the time/frequency view.
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- **Region selection** — box a time *and* frequency range with the mouse.
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- **Filtered playback** — play just the selected region, band-limited to the
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selected frequency box via an FFT bandpass. What you hear is what you'd export.
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- **Waveform scope** — toggleable time-domain view beneath the spectrum.
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- **Marker / ruler** and a **spectrum slice (PSD)** readout.
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- **Export** — save the view as a PNG, or the selected region as a WAV.
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- **Headless render mode** — produce an annotated PNG from the CLI with no
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window, no GL, and no X server. Pure CPU; runs in CI, containers, or over SSH.
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- **Broad input** — WAV directly (8/16-bit PCM, 32-bit float; stereo downmixed to
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mono); other formats transcoded via `ffmpeg` if it's on `PATH`. Drag-and-drop.
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- **Cross-platform** — Linux/desktop, Windows, and a WebAssembly build.
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---
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## Building
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The build is driven by a checked-in Makefile. `premake5` is **not** required to
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build — only to regenerate the makefiles.
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```bash
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make -f rspektrum.make config=debug_x64 # -> bin/Debug/rspektrum
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make -f rspektrum.make config=release_x64 # -> bin/Release/rspektrum
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```
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Web (WebAssembly) build:
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```bash
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./build_web.sh # emscripten; emits the WebAssembly bundle
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```
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> The release build enables `-O2`, which turns on extra warnings
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> (`-Wformat-truncation`) that the debug build doesn't. Build release before
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> declaring a change clean.
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---
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## Usage (desktop GUI)
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```bash
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./bin/Debug/rspektrum [input.wav]
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```
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Load a file by passing it on the command line, dragging a `.wav` onto the window,
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or pressing **O** for the file browser. Try the bundled sample:
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```bash
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./bin/Debug/rspektrum mlnl_samples.wav # in-repo WAV with an embedded mLnL chunk
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```
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### Controls
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| Input | Action |
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|-------|--------|
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| **O** | Open file browser |
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| **Mouse wheel** | Zoom time/frequency |
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| **Alt+drag** / **middle-drag** | Pan the view |
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| **LMB drag** | Select a time + frequency region |
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| **Space** | Play / stop the selected region |
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| **Hover an annotation** | Tooltip with that frame's mLnL detail |
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| **P** | Show / hide the waveform scope |
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| **M** | Marker / ruler tool |
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| **S** | Spectrum slice (PSD) |
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| **E** | Export PNG |
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| **W** | Export selection as WAV |
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| **Home** | Reset view (fit all) |
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| **End** | Zoom to start |
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| **F11** | Toggle fullscreen |
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| **F1** | About / help |
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| **Esc** | Clear selection / close dialog |
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Most controls are also available as buttons in the left sidebar (colormap, floor,
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dynamic range, annotation opacity, grid, …).
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---
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## Usage (headless render)
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`--render` writes the spectrogram straight to a PNG **with no window, no GL
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context, and no X server**. It computes the STFT, colorizes the bitmap, bakes the
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annotation overlay onto it, and exports — all on the CPU — so it runs anywhere
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(CI, a bare SSH session, a container with no display):
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```bash
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./bin/Debug/rspektrum --render OUT.png INPUT.wav [options]
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```
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The output is the **real spectrogram bitmap** at native STFT resolution (not a
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screenshot of the UI), so it carries no sidebar/scope chrome — just the
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time–frequency image with the annotation overlay.
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| Flag | Effect |
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|------|--------|
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| `-r, --render OUT.png` | Render to `OUT.png` and exit (no window/GL/X) |
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| `-a, --annotations` | Force the annotation overlay **on** |
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| `--no-annotations` | Force the overlay off |
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| `--annotation-opacity=V` | Overlay strength `0..1` (default `0.5`) |
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| `--annotation-kinds=LIST` | Comma-separated kinds to draw (default: all) |
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| `--width N` | Resize output to `N` px wide (default: native STFT size) |
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| `-h, --help` | Usage |
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Annotation boxes are drawn **outline + label only** (no translucent fill): mLnL
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captures contain many overlapping full-band boxes whose fills would alpha-stack
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to opaque and bury the signal, so the outline marks each region while the
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spectrogram reads through.
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```bash
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# everything, brighter overlay
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./bin/Debug/rspektrum --render /tmp/all.png mlnl_samples.wav --annotation-opacity=0.7
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# only on-air frames and failed assertions
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./bin/Debug/rspektrum --render /tmp/tx.png mlnl_samples.wav \
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--annotation-kinds=tx_frame,assertion_failed
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```
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Annotation kinds: `tx_frame`, `tx_burst`, `control`, `channel_up`,
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`channel_down`, `assertion_passed`, `assertion_failed`, `impairment_fire`,
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`gain_change`, `unknown`.
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> The hover tooltip only appears with a live mouse over a box, so it cannot show
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> up in a static `--render`. To verify tooltip behaviour you need a real (or
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> virtual) display driving the GUI — see below.
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---
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## Driving the GUI headlessly (agents / CI)
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The app can be run, screenshotted, and clicked on a virtual X display with no
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monitor or GPU (Mesa software GL under Xvfb). The full playbook lives in
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[`AGENTS.md`](AGENTS.md); the working reference implementation is
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[`shot_input.sh`](shot_input.sh).
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The loop in one breath:
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```bash
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Xvfb :99 -screen 0 1280x800x24 >/tmp/xvfb.log 2>&1 & # 1. fake screen
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DISPLAY=:99 ./bin/Debug/rspektrum mlnl_samples.wav \
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>/tmp/app.log 2>&1 & # 2. run on it
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sleep 2 # 3. reach a steady frame
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DISPLAY=:99 import -window root /tmp/shot.png # 4. grab the frame
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```
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Prerequisites (Debian/Ubuntu): `sudo apt-get install xvfb imagemagick xdotool`
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(plus `libgl1-mesa-dri` and `LIBGL_ALWAYS_SOFTWARE=1` if GL fails / frames are
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black). Synthesize input with `xdotool` against `DISPLAY=:99` to exercise UI
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paths.
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---
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## Technical notes
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- **STFT** — Hann-windowed, 2048-point FFT with 50% overlap by default;
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frequency resolution `sampleRate / fftSize` Hz per bin. Amplitude in dB.
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- **Axes** — X = time (s), Y = frequency (Hz, scaled to the file's Nyquist),
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colour = amplitude.
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- **Playback / WAV export** share one processing path: the selected time span,
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FFT-bandpassed to the selected frequency box, peak-normalised.
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- **mLnL parsing** — walks the WAV's RIFF chunks for the four-CC `mLnL` chunk
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(UTF-8 JSON Lines); unknown chunks are skipped, so annotated files stay
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standards-compliant audio everywhere else.
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---
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## Source layout
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```
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src/
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spectrogram.c # entry point, main loop, CLI args, headless render
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stft.c / fft.c # STFT + FFT
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render.c # spectrogram, annotations, tooltips, scope
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ui.c # sidebar, file browser, buttons
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audio.c # WAV load (ffmpeg fallback), bandpass, playback, WAV export
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mlnl.c / mlnl.h # mLnL annotation chunk parser
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platform_*.c # per-OS shims (linux / win32 / web)
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```
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See [`raylib_for_desktop_applications.md`](raylib_for_desktop_applications.md)
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for the performance / idle-CPU lessons behind the desktop build, and
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[`AGENTS.md`](AGENTS.md) for the headless-testing playbook.
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