Fix CI build failure by adding ALSA dependency and testing feature paths

Previous: The GitHub Actions workflow was building with default features
including CPAL, which requires ALSA development headers on Linux. The
ubuntu-latest runner lacked libasound2-dev, causing CI builds to fail.
Additionally, the production FreeBSD target uses a different build path
without CPAL, which wasn't being tested in CI.

Changed: Updated .github/workflows/rust.yml to install libasound2-dev
before the build step in the existing build job. Added a new
build-no-default-features job that tests the no-default-features build
path used in FreeBSD production. Both paths are now exercised on every PR.

See: changelog/20260503-ci-alsa-dep.md

Author: knz

.github/workflows/rust.yml

@@ -16,7 +16,20 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
+    - name: Install ALSA development headers
+      run: sudo apt-get update && sudo apt-get install -y libasound2-dev
     - name: Build
       run: cargo build --verbose
     - name: Run tests
       run: cargo test --verbose
+
+  build-no-default-features:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Build (no default features)
+      run: cargo build --no-default-features --verbose
+    - name: Run tests (no default features)
+      run: cargo test --no-default-features --verbose

changelog/20260503-ci-alsa-dep.md

@@ -0,0 +1,52 @@
+---
+title: CI build fails: missing ALSA dependency for CPAL
+date: 2026-05-03
+---
+
+# CI build failure: missing ALSA dev headers
+
+## Task Specification
+
+User reports that the GitHub Actions CI build fails because the runner
+doesn't have the ALSA development headers installed. The recent
+addition of CPAL (default feature) requires `libasound2-dev` on Linux
+to compile.
+
+## Context
+
+- CI workflow: `.github/workflows/rust.yml` runs on `ubuntu-latest`
+- Cargo.toml: `cpal = { version = "0.16", optional = true }` is a default feature
+- CPAL on Linux links against ALSA, which requires the `libasound2-dev`
+  package at build time.
+- The project's primary target is FreeBSD; Linux CI is just a sanity
+  check, but we still want it to pass.
+
+## Options Considered
+
+1. Install `libasound2-dev` in the CI workflow before `cargo build`.
+2. Disable the `cpal` default feature in CI via `--no-default-features`.
+3. Both: install the dep AND add a `--no-default-features` job to keep
+   that build path tested too.
+
+## Decision
+
+User selected option 3: install ALSA for the main job AND add a second
+job that builds with `--no-default-features`.
+
+Rationale: CPAL is the default feature for Linux developers, but the
+production target is FreeBSD which uses the no-CPAL build path. Both
+paths should be exercised on every PR. Keeping the existing job named
+`build` preserves any branch-protection check that pins to the job
+name; the new job is `build-no-default-features`.
+
+## Files Modified
+
+- `.github/workflows/rust.yml`: added `libasound2-dev` install step to
+  the existing `build` job; added a new `build-no-default-features`
+  job that runs `cargo build` and `cargo test` with
+  `--no-default-features` (no ALSA needed).
+
+## Current Status
+
+Done. Awaiting user to commit and push to verify CI passes.
+