docs: fold the saturation-test findings into the audio taxonomy

A blind resample tested whether the nine-cluster taxonomy was representative or an artifact of the first sweep. Ten agents drew 108 fresh reports through five different doors per direction, mostly non-Arch and 2024-2026, none shown the clusters. Zero forced a new cluster. About 70 re-found existing entries. The other 34 were new distinct root causes that all fit existing clusters.

I folded the 34 new entries in, 16 input and 18 output, each tagged with its cluster and remedy class, and recorded the test and its verdict. The clusters are complete and stable. Entries keep growing under them without changing the design.

1 files changed, 52 insertions, 0 deletions

diff --git a/docs/design/2026-07-10-audio-failure-taxonomy.org b/docs/design/2026-07-10-audio-failure-taxonomy.org
index c504f81..efb6e0a 100644
--- a/docs/design/2026-07-10-audio-failure-taxonomy.org
+++ b/docs/design/2026-07-10-audio-failure-taxonomy.org
@@ -8,6 +8,14 @@ A catalogue of real, user-reported ways Linux audio input (microphone) and outpu
 
 Target: 50 input failure modes and 50 output failure modes, or exhaustion. Each entry names the layer, the symptom as a user reports it, the root cause, the known resolution, and a source.
 
+** Saturation test (2026-07-10)
+
+To check whether the nine-cluster-per-direction taxonomy was representative or an artifact of how we first sampled, a blind resample: ten agents drew 108 fresh failure reports through five different doors per direction (specific hardware lines, external devices, non-Arch distros, broad community Q&A, and call/gaming apps), weighted toward 2024-2026 and non-Arch sources, none of them shown the clusters or the existing entries. Every result was then classified against the existing 18 clusters.
+
+Result: zero of 108 needed a new cluster. Roughly 70 re-found entries already in the catalogue (many hitting the exact same bug and source URL we had cited independently), which is entry-level saturation. The other ~34 were genuinely new distinct root causes, and all of them slotted into existing clusters. The new results spread across every cluster and concentrated where the original catalogue did (cluster 1 firmware/driver, and the app cluster). The app cluster grew densest, which confirms the Chrome incident that started this was representative, not a fluke.
+
+Conclusion: the clusters — what the doctor's probe ladder and verdict structure rest on — are complete and stable. Entries will keep growing (hardware × kernel × app is unbounded), but the design can rest on the taxonomy. The ~34 new entries the sweep surfaced are folded in below, under a "Saturation resample additions" heading in each direction, each carrying its cluster and remedy class inline.
+
 * Input (microphone) failure modes
 
 Built 2026-07-10 from a parallel research sweep across eight layers (kernel/driver/firmware, ALSA, PipeWire/WirePlumber, Bluetooth, USB, app/portal, hardware, config/misc). 64 raw entries deduped to 58 distinct root causes. Each names the layer, the user-reported symptom, the cause, the known fix (with the concrete command where one exists), whether the fix needs root or a reboot, and a source. The =sudo/reboot= field is the first triage signal: a no-sudo, no-reboot fix is a candidate for an auto or guide remedy; a both/physical fix can only ever be a guide.
@@ -94,6 +102,27 @@ Built 2026-07-10 from a parallel research sweep across eight layers (kernel/driv
 - XDG_RUNTIME_DIR unset in ssh/cron/non-login session (no). Recording works in the desktop terminal but fails from ssh or cron. Non-login sessions skip pam_systemd, so the socket in =/run/user/<uid>= isn't found. Fix: run as the seat user with =XDG_RUNTIME_DIR= set. [[https://bbs.archlinux.org/viewtopic.php?id=286176][arch 286176]]
 - Auto-gain (AGC) pulling the mic level toward zero (no). The mic gets progressively quieter; something keeps lowering the input volume. An app or WirePlumber is allowed to auto-adjust the source gain and only ratchets down. Fix: a WirePlumber access rule blocking the client from changing gain. [[https://www.lumeh.org/wiki/audio/stop-adjusting-my-microphone/][lumeh]]
 
+** Saturation resample additions (2026-07-10)
+
+Genuinely-new input root causes from the blind resample, each tagged with the cluster it fits and its remedy class (so this doubles as their triage). Zero forced a new cluster.
+
+- Mic boost too high, records static/distortion (cluster 3 · AUTO). The inverse of boost-at-zero. Fix: lower Mic Boost. [[https://bbs.archlinux.org/viewtopic.php?id=211318][arch 211318]]
+- App auto-gain zeroes the mic, Zoom/Discord (cluster 7 · GUIDE). The app's own auto-input-adjust drives the level to 0. Fix: disable "automatically adjust microphone volume" / input-sensitivity. [[https://community.zoom.com/t5/Meetings/Zoom-for-Linux-not-working-well-with-newer-distributions/m-p/22805][zoom community]]
+- App selects the wrong input, "monitor of output", Teams (cluster 7 · GUIDE). Fix: set the device before launch, avoid the in-call chooser. [[https://learn.microsoft.com/en-us/answers/questions/183216/in-ms-teams-for-linux-microphone-stopped-working][ms teams]]
+- App requires PulseAudio, fails on bare ALSA, Signal/Webex (cluster 7 · GUIDE). WebRTC won't enumerate devices without the Pulse layer. Fix: install pipewire-pulse. [[https://github.com/signalapp/Signal-Desktop/issues/5099][signal 5099]]
+- Browser WebRTC captures one channel only, Jitsi/Firefox (cluster 7 · GUIDE). Firefox-specific channel handling. Fix: Chrome as workaround. [[https://github.com/jitsi/jitsi-meet/issues/16828][jitsi 16828]]
+- Mic classified as an output device, Pop COSMIC (cluster 2 · GUIDE). A desktop-environment device-role bug. Fix: none confirmed; tracked upstream. [[https://github.com/pop-os/cosmic-epoch/issues/1368][cosmic 1368]]
+- SOF topology-file mismatch, DMIC visible but silent (cluster 1 · PRIV, REBOOT-TAIL). The firmware is present but the wrong .tplg loads. Fix: swap the topology file in firmware-sof. [[https://bugzilla.redhat.com/show_bug.cgi?id=1772498][rh 1772498]]
+- Webcam mic needs a USB init-delay quirk, Logitech C922 (cluster 1 · REBOOT-TAIL). Fix: kernel with USB_QUIRK_DELAY_INIT for the device. [[https://bugs.launchpad.net/bugs/1885259][lp 1885259]]
+- USB interface implicit-feedback / clock-source stutter, Behringer UMC (cluster 4 · REBOOT-TAIL). Fix: =implicit_fb= modprobe, or kernel 5.19+. [[https://nandakumar.org/blog/2023/01/upgrade-linux-for-umc202hd.html][nandakumar]]
+- USB dual-channel device won't do input and output at once until a profile toggle, Elgato Wave (cluster 4 · AUTO). Fix: toggle the Pro Audio vs Duplex profile. [[https://forum.level1techs.com/t/elgato-wave-3-fails-to-work-as-microphone/221807][level1techs]]
+- USB mic not reliably enumerated, a port/controller issue or a PipeWire add-race (cluster 4 · AUTO). Fix: restart PipeWire, or a different port. [[https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/1534][pw 1534]]
+- PipeWire buffer/scheduling failure, source active but no samples (cluster 5 · GUIDE). "port_use_buffers" / "scheduling stopped node" in the log. Fix: unresolved upstream. [[https://github.com/NixOS/nixpkgs/issues/271847][nixpkgs 271847]]
+- Sudo-run audio tools corrupt the WirePlumber state (cluster 9 · AUTO). Fix: =rm -r ~/.local/state/wireplumber=; never run audio tools under sudo. [[https://www.kubuntuforums.net/forum/currently-supported-releases/kubuntu-24-04-nitpick-noble-lts/hardware-support-bg/681510-kubuntu-24-04-microphone-volume-at-100-per-cent-on-every-reboot][kubuntu]]
+- Audio-group membership blocks per-session access, older udev/ConsoleKit distros (cluster 9 · PRIV). Fix: remove the user from the =audio= group. [[https://wiki.ubuntu.com/Audio/TheAudioGroup][ubuntu audio group]]
+- Windows fast-startup wedges audio on a dual-boot (cluster 9 · GUIDE). Fix: disable Windows fast boot, or reload the sof module. [[https://bbs.archlinux.org/viewtopic.php?id=279824][arch 279824]]
+- Dead mic transducer / faulty mic module (cluster 8 · GUIDE). Fix: hardware defect, replaced under warranty. [[https://community.frame.work/t/fedora-41-13th-gen-intel-core-microphone-not-working/64010][framework 64010]]
+
 * Input triage
 
 The 58 input failure modes sorted into nine symptom clusters, each owned by a probe the doctor runs (or would run). Every entry carries a remedy class:
@@ -387,6 +416,29 @@ Probe: none in-stack; the tail on a healthy verdict. The output mirror of input
 - Chromium doesn't follow the default-sink change :: GUIDE — reassign the stream in pavucontrol.
 - Electron app routed to the wrong sink :: GUIDE — move the stream in pavucontrol.
 
+** Saturation resample additions (2026-07-10)
+
+Genuinely-new output root causes from the blind resample, each tagged with the cluster it fits and its remedy class. Zero forced a new cluster.
+
+- App picks the wrong audio backend, Spotify (cluster 9 · GUIDE). The app's built-in backend mis-routes. Fix: force the pulseaudio backend in the launch flags (=--audio-api=pulseaudio=). [[https://bbs.archlinux.org/viewtopic.php?id=285730][arch 285730]]
+- A PipeWire regression breaks game audio, Proton XAudio2 titles (cluster 9 · GUIDE). Fix: downgrade PipeWire, or update to the fixed release. [[https://github.com/ValveSoftware/Proton/issues/8730][proton 8730]]
+- App muted in the desktop per-app mixer, KDE Chrome (cluster 9 · AUTO). The Flatpak permission is fine; the app's stream is muted in the DE volume applet. Fix: unmute the app there. [[https://github.com/flathub/com.google.Chrome/issues/297][chrome 297]]
+- App connection stale after an audio-stack update, Firefox (cluster 9 · AUTO). Fix: restart the app or the audio daemon. [[https://forum.endeavouros.com/t/solved-no-audio-in-firefox-from-pipewire-or-pulseaudio-update/26032][endeavour 26032]]
+- Output defaults to the wrong digital out, needs alsactl init, Framework 16 (cluster 2 · AUTO). Fix: =alsactl init=, then select the analog output. [[https://community.frame.work/t/solved-framework-16-ai-300-series-ubuntu-24-04-speakers-work-but-not-headphones/81363][framework 81363]]
+- WirePlumber disabled in config, no enumeration, NixOS (cluster 2 · AUTO). Fix: enable wireplumber in the config, rebuild. [[https://github.com/NixOS/nixpkgs/issues/402999][nixpkgs 402999]]
+- A distro update drops an audio package, openSUSE =wireplumber-audio= (cluster 1 · PRIV). Fix: reinstall and lock the package. [[https://forums.opensuse.org/t/no-output-or-input-devices-after-zypper-dup-only-dummy-output-in-pipewire-on-tumbleweed/185154][opensuse 185154]]
+- USB audio module not auto-loaded after a kernel update (cluster 1 · PRIV). Fix: add =snd_usb_audio= to =modules-load.d=. [[https://forums.linuxmint.com/viewtopic.php?t=443590][mint 443590]]
+- Stray =model=generic= modprobe forces the wrong codec (cluster 1 · REBOOT-TAIL). Left by OEM/installer tooling. Fix: delete the leftover =/etc/modprobe.d= line. [[https://bugs.launchpad.net/bugs/2092728][lp 2092728]]
+- SOF driver aborts when the codec is hda_generic, Acer Swift (cluster 1 · REBOOT-TAIL). Fix: kernel 5.8+; =dmic_detect=0= workaround. [[https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1877757][lp 1877757]]
+- Cirrus CS35L56 smart-amp firmware not applied, ROG G14 2024 (cluster 1 · REBOOT-TAIL). A newer amp than the CS35L41 already catalogued. Fix: newer kernel + firmware. [[https://www.mail-archive.com/debian-kernel@lists.debian.org/msg139811.html][debian-kernel]]
+- Creative CA0132 card needs a kernel quirk, AE-5 Plus (cluster 1 · GUIDE). Reuses an existing PCI id with a different config. Fix: no userspace fix; kernel patch. [[https://forum.manjaro.org/t/soundblaster-creative-ae-5-plus-no-sound/60516][manjaro 60516]]
+- ALC4080 enumerates as USB not HDA, front-panel node not exposed (cluster 4 · AUTO). Fix: an explicit ALSA sink in =pipewire.conf= pointing at the FP device. [[https://discussion.fedoraproject.org/t/headphone-audio-not-working-asus-rog-strix-z590-f-alc4080/76380][fedora 76380]]
+- GPU HDMI audio KAE regression, Intel Arc DG2 (cluster 7 · GUIDE). Fix: kernel fix disables KAE for DG2; update kernel. [[https://www.phoronix.com/news/Intel-DG2-Audio-Fix-Linux-KAE][phoronix]]
+- USB DAC silent at a specific sample rate, FiiO 44.1k (cluster 8 · AUTO). Fix: set =allowed-rates=. [[https://bbs.archlinux.org/viewtopic.php?id=180561][arch 180561]]
+- BIOS firmware bug, crackle or dead speakers fixed by a BIOS update, MSI GF63 (cluster 1 · GUIDE). Broke on Windows too. Fix: flash the vendor BIOS update. [[https://forums.linuxmint.com/viewtopic.php?t=424474][mint 424474]]
+- USB sound device not reliably enumerated after boot, an init race, Creative/Schiit (cluster 5 · GUIDE). Fix: replug; pin the profile. [[https://forum.zorin.com/t/usb-soundcard-creative-sound-blaster-hd-not-always-recognized-after-boot/66177][zorin 66177]]
+- Audio-group membership blocks access, older udev/ConsoleKit distros (cluster 9 · PRIV). The same cross-cutting trap the input side hit. Fix: remove the user from the =audio= group. [[https://wiki.ubuntu.com/Audio/TheAudioGroup][ubuntu audio group]]
+
 * Sources
 
 Every entry carries its source inline as an org link. Reports span the Arch/Manjaro/EndeavourOS/Fedora/Ubuntu/Mint/openSUSE forums, askubuntu, the PipeWire and WirePlumber docs, ALSA and Flatpak issue trackers, kernel bug trackers, and vendor forums (NVIDIA, Dell). Collected 2026-07-10.