Fix CI compile error and unbreak Nix builds from Windows clones

.gitattributes

@@ -0,0 +1,11 @@
+# Nix embeds the contents of these files verbatim into derivation build
+# scripts.  A CR that survives into such a script reaches bash as a literal
+# $'\r' command and the build dies with exit code 127, so a Windows clone made
+# with the Git default core.autocrlf=true cannot build the images at all.
+# Normalise everything to LF in the working tree, not just in the blobs.
+* text=auto eol=lf
+
+# The CMD entry points are the exception: cmd.exe parses multi-line blocks
+# reliably only with CRLF.
+*.cmd text eol=crlf
+*.bat text eol=crlf

.github/workflows/ci.yml

@@ -38,6 +38,11 @@ jobs:
         # Windows PowerShell 5.1 is what qubix-up.cmd runs; pwsh is the
         # developer console.  Both must stay happy.
         shell: [powershell, pwsh]
+    defaults:
+      run:
+        # A step's own `shell:` accepts no contexts at all, so the matrix
+        # value has to arrive through the job defaults instead.
+        shell: ${{ matrix.shell }}
     steps:
       - uses: actions/checkout@v4
 
@@ -51,7 +56,6 @@ jobs:
           if ($results.Count -gt 0) { exit 1 }
 
       - name: unit checks
-        shell: ${{ matrix.shell }}
         run: |
           & ./tests/qubixctl.Tests.ps1
           if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }

README.md

@@ -43,7 +43,9 @@ WSL is not required on the host. It stays available as the developer loop
   `tools/qubix-up.cmd`, the double-click launcher that elevates itself.
 - GitHub Actions: `ci` (flake check, manifest drift, PowerShell lint + unit
   checks) and `release` (builds and attaches the images to a tagged release).
-- A stable xrdp audio baseline using PulseAudio, not PipeWire.
+- A stable xrdp audio baseline using PulseAudio, not PipeWire, and xrdp built
+  without the MP3/Opus encoders so that mstsc negotiates PCM and actually
+  plays it (see *Why PCM-only audio*).
 - Separate `user` and `rdp` accounts (pinned UIDs) to avoid session
   cross-contamination.
 - A NixOS smoke test for users, xrdp, Spotify, Openbox, Avahi and the kiosk
@@ -135,6 +137,40 @@ C:\HyperV\Qubix\
 - User IDs are pinned (`user` = 1000, `rdp` = 1001) so a persistent home never
   changes owner when the user list changes.
 
+## Continuous Integration
+
+`ci` runs on pull requests, on pushes to `main`, and on manual dispatch. It
+does **not** run on a push to a feature branch, so work on a branch stays
+unchecked until a PR exists - open one early if you want the signal.
+
+| Job | Runner | What it does |
+| --- | --- | --- |
+| `flake check, manifest sync, home seed` | ubuntu | `nix flake check`, fails on `manifest.json` drift, builds the home seed |
+| `controller lint + unit checks (powershell)` | windows | unit checks under Windows PowerShell 5.1, the shell `qubix-up.cmd` actually uses |
+| `controller lint + unit checks (pwsh)` | windows | the same checks under pwsh 7, plus PSScriptAnalyzer |
+
+Driving it from the terminal with the GitHub CLI:
+
+```bash
+gh run list --limit 10                 # recent runs, newest first
+gh run watch                           # follow the run for the current branch
+gh run view <run-id> --log-failed      # only the failing steps
+gh run rerun <run-id> --failed         # retry just the failed jobs
+gh workflow run ci.yml --ref <branch>  # manual dispatch
+gh pr checks <pr>                      # per-check status for a PR
+```
+
+A run that fails in 0s with no jobs, and a workflow listed under its file path
+instead of its `name:`, means GitHub could not compile the YAML - the run log
+is empty in that case, so lint locally instead:
+
+```bash
+nix run nixpkgs#actionlint
+```
+
+`actionlint` catches the whole class of errors GitHub reports only as a failed
+run, such as using a context where none is allowed.
+
 ## Publishing A Release
 
 ```bash
@@ -296,6 +332,29 @@ PipeWire       -> disabled
 EasyEffects is intentionally not the active DSP baseline here. It is
 PipeWire-oriented, while this xrdp audio path expects PulseAudio.
 
+### Why PCM-only audio
+
+nixpkgs builds xrdp with `--enable-mp3lame` and `--enable-opus`. With those
+available, Windows' `mstsc` negotiates `WAVE_FORMAT_MPEGLAYER3` and then plays
+nothing at all, while every diagnostic inside the guest looks perfectly
+healthy: `xrdp-sink` is the default sink, it is not muted, it sits at 100%, it
+moves between IDLE and RUNNING in time with the track, chansrv accepts the
+socket and logs `round trip time 0`. Only the host is silent, and the Windows
+volume mixer shows the mstsc slider with no level on it. See
+[neutrinolabs/xrdp#965](https://github.com/neutrinolabs/xrdp/issues/965).
+
+`profiles/audio/pulseaudio-xrdp.nix` therefore drops both encoders, which
+leaves PCM as the only negotiable format. PCM is ~176 kB/s - irrelevant next to
+the video channel.
+
+The override has to be a `nixpkgs.overlays` entry rather than the obvious
+`services.xrdp.package`. The NixOS module declares that option but then
+hardcodes `pkgs.xrdp` in the `ExecStart` of both `xrdp.service` and
+`xrdp-sesman.service`, so setting it rebuilds `confDir` only and the daemons
+keep running the untouched build - the option silently does nothing. A fix is open
+upstream as [nixpkgs#452303](https://github.com/NixOS/nixpkgs/pull/452303); when it
+lands, this overlay can become a plain `services.xrdp.package` assignment.
+
 ### Nix-Generated JSON
 
 Nix is the source of truth for the manifest. `manifest.json` is the output of

profiles/audio/pulseaudio-xrdp.nix

@@ -12,6 +12,31 @@ lib.mkIf (config.qubix.audio == "pulseaudio-xrdp") {
   # profile only wires the audio path into it.
   services.xrdp.audio.enable = true;
 
+  # mstsc negotiates WAVE_FORMAT_MPEGLAYER3 whenever xrdp offers it and then
+  # plays nothing at all.  Everything inside the guest looks healthy while this
+  # happens - the sink runs, it is not muted, chansrv accepts the socket and
+  # reports a round trip time - but the host stays silent, because mstsc simply
+  # drops the MP3 stream (neutrinolabs/xrdp#965).  Building xrdp without the MP3
+  # and Opus encoders leaves PCM as the only negotiable format, and every RDP
+  # client decodes that.  PCM costs ~176 kB/s, which is nothing next to the
+  # video channel this appliance already pushes.
+  #
+  # This must be an overlay, not services.xrdp.package: the NixOS xrdp module
+  # declares that option but hardcodes pkgs.xrdp in the ExecStart lines of both
+  # xrdp.service and xrdp-sesman.service, so setting the option rebuilds only
+  # confDir while the daemons keep running the unmodified build.  A fix is
+  # already open upstream as https://github.com/NixOS/nixpkgs/pull/452303;
+  # once it lands this can go back to a plain services.xrdp.package assignment.
+  nixpkgs.overlays = [
+    (_final: prev: {
+      xrdp = prev.xrdp.overrideAttrs (old: {
+        configureFlags = builtins.filter
+          (f: f != "--enable-mp3lame" && f != "--enable-opus")
+          old.configureFlags;
+      });
+    })
+  ];
+
   security.rtkit.enable = true;
 
   services.pulseaudio.enable = true;