Windows port Phase 0: platform-select the audio backend

Make the tree compile for Windows without touching core logic, by
confining all Linux/PipeWire assumptions behind cfg gates and a single
platform-selected backend alias. No new dependencies — the cpal/WASAPI
backend lands in Phase 1; this ships a no-op stub.

- Cargo.toml: move pipewire + rfd(xdg-portal) under cfg(unix); add a
  cfg(windows) rfd using the Win32 dialog backend.
- audio: gate pipewire_impl to unix, add a cpal_impl stub for windows,
  and select between them via the new PlatformAudioBackend alias.
- core: use PlatformAudioBackend instead of the concrete PipeWireBackend.
- lib: gate the unix-only 0o600 log-file mode code (+ its test); Windows
  logs inherit the directory ACL.
- audio_probe: gate this PipeWire diagnostic to unix with a stub main.
- app: open URLs via rundll32 on windows, xdg-open on unix (shell-free).
- ci: add .gitea/workflows/windows-build.yml (M1) — build + lib tests for
  x86_64-pc-windows-msvc, with CMAKE_POLICY_VERSION_MINIMUM=3.5 for the
  vendored libopus build. Needs a windows act_runner to actually run.

Linux build/clippy/tests green (316/316). The Windows path is verified by
inspection only (no local Windows toolchain); CI is the real gate.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/windows-build.yml

@@ -0,0 +1,85 @@
+name: windows-build
+
+# Milestone M1 of the Windows port (see docs/handoff windows-migration-plan):
+# prove the tree compiles for `x86_64-pc-windows-msvc` and the unit tests pass.
+# The audio backend is the Phase 0 `CpalBackend` stub for now — this job guards
+# the *compile* boundary (cfg gating, platform deps, the PlatformAudioBackend
+# alias) so a Unix-only assumption can't sneak back in and break Windows.
+#
+# RUNNER REQUIREMENT: this needs a Windows act_runner registered with the
+# `windows-latest` label (the Linux `cargo-deny` job's container approach does
+# NOT apply here — Windows jobs run on the host, not a Linux container). If your
+# runner advertises a different label, change `runs-on` below. Until a Windows
+# runner exists this workflow is simply skipped/queued, not a failure of the
+# Linux CI.
+#
+# BUILD-HOST REQUIREMENTS (validated by the opus spike, see
+# peerspeak-windows-opus-spike.md):
+#   - MSVC C toolchain (Visual Studio Build Tools) — to compile vendored libopus.
+#   - CMake on PATH — `audiopus_sys` builds libopus from source via cmake.
+#   - CMAKE_POLICY_VERSION_MINIMUM=3.5 (set below) — the vendored libopus declares
+#     an ancient `cmake_minimum_required` that CMake >= 4.0 refuses without it.
+# GitHub-hosted `windows-latest` images ship MSVC + CMake; a self-hosted runner
+# must provide both.
+
+on:
+  push:
+    # `main` plus the in-progress port branches, so the Windows path is exercised
+    # before merge rather than only after.
+    branches: [main, "windows-port-**"]
+  pull_request:
+  # Allow manual runs from the Gitea Actions UI.
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+env:
+  CARGO_TERM_COLOR: always
+  # The vendored libopus (audiopus_sys -> cmake) uses cmake_minimum_required < 3.5,
+  # which CMake 4.x rejects unless this is set. See the opus spike report.
+  CMAKE_POLICY_VERSION_MINIMUM: "3.5"
+
+jobs:
+  windows-build:
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Rust (MSVC, pinned to repo toolchain if present)
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          targets: x86_64-pc-windows-msvc
+          components: clippy
+
+      - name: Show toolchain + build prerequisites
+        shell: bash
+        run: |
+          set -euo pipefail
+          rustc --version
+          cargo --version
+          # libopus is built from source via cmake; fail early with a clear
+          # message if the runner lacks it rather than deep in the opus build.
+          if ! command -v cmake >/dev/null 2>&1; then
+            echo "::error::cmake not found on PATH. The opus crate builds libopus from source via cmake; install CMake on this runner."
+            exit 1
+          fi
+          cmake --version
+
+      # Build on a *locked* tree so the pinned, vetted Cargo.lock versions are what
+      # get compiled — same supply-chain stance as the cargo-deny job.
+      - name: Build (all targets, msvc)
+        run: cargo build --all-targets --locked --target x86_64-pc-windows-msvc
+
+      # Unit (lib) tests only: the `transport_loopback` integration tests stand up
+      # real iroh/QUIC endpoints and need working loopback networking, which isn't
+      # guaranteed on a CI runner. Add `--tests` here once a networked Windows
+      # runner is confirmed.
+      - name: Unit tests (lib, msvc)
+        run: cargo test --lib --locked --target x86_64-pc-windows-msvc
+
+      # Informational for now (not `-D warnings`): the Windows tree may surface
+      # platform-specific lints we haven't triaged. Tighten to deny-warnings once
+      # it's clean.
+      - name: Clippy (msvc)
+        run: cargo clippy --all-targets --locked --target x86_64-pc-windows-msvc

Cargo.toml

@@ -30,17 +30,12 @@ bytes = "1.11.1"
 dirs = "6.0.0"
 iced = { version = "0.14.0", features = ["canvas", "image"] }
 # W4 custom avatars: decode/resize an arbitrary user image (png/jpeg only to keep
-# the codec surface small) and a native file picker (xdg-portal backend, no GTK).
+# the codec surface small). The matching native file picker (`rfd`) is platform-
+# gated below — its backend differs per OS (xdg-portal on Linux, Win32 on Windows).
 image = { version = "0.25", default-features = false, features = ["png", "jpeg"] }
-rfd = { version = "0.17", default-features = false, features = ["xdg-portal"] }
 iroh = "1.0.0-rc.0"
 iroh-gossip = "0.99.0"
 opus = "0.3.1"
-# v0_3_49 exposes `Buffer::requested()` (the graph's per-cycle quantum), used by
-# the playback RT callback to fill exactly what the device asks for instead of
-# pinning the buffer to a hard-coded 1024-frame quantum (crackle on non-1024
-# hardware). The field has existed in libpipewire since 0.3.49 (2022).
-pipewire = { version = "0.9", features = ["v0_3_49"] }
 rand = "0.10.1"
 ringbuf = "0.5.0"
 serde = { version = "1.0.228", features = ["derive"] }
@@ -48,3 +43,24 @@ serde_json = "1.0.150"
 thiserror = "2.0.18"
 tokio = { version = "1.52.3", features = ["full"] }
 tokio-stream = "0.1.18"
+
+# --- Platform-specific dependencies -----------------------------------------
+# Audio and the native file-picker backends differ per OS. Everything else in the
+# app talks to the `AudioBackend` trait and the `PlatformAudioBackend` alias (see
+# `src/audio/mod.rs`), so platform selection is confined to these few lines.
+
+[target.'cfg(unix)'.dependencies]
+# Linux audio backend. v0_3_49 exposes `Buffer::requested()` (the graph's per-cycle
+# quantum), used by the playback RT callback to fill exactly what the device asks
+# for instead of a hard-coded 1024-frame quantum (crackle on non-1024 hardware).
+# The field has existed in libpipewire since 0.3.49 (2022).
+pipewire = { version = "0.9", features = ["v0_3_49"] }
+# Native file picker via the XDG desktop portal (no GTK) on Linux.
+rfd = { version = "0.17", default-features = false, features = ["xdg-portal"] }
+
+[target.'cfg(windows)'.dependencies]
+# Native file picker using the built-in Win32 dialog backend on Windows.
+rfd = { version = "0.17", default-features = false }
+# NOTE: the Windows audio backend (cpal/WASAPI) lands in Phase 1. Until then the
+# Windows build uses the no-op `CpalBackend` stub in `src/audio/cpal_impl.rs`,
+# which needs no extra dependency.

src/app/mod.rs

@@ -1350,14 +1350,30 @@ fn update(state: &mut AppState, message: AppMessage) -> Task<AppMessage> {
             // Defence in depth: only ever hand http(s) URLs to the opener. The
             // link span's href came from `linkify`, which only emits http/https,
             // but re-check here so this can't be widened into launching arbitrary
-            // schemes/args. `xdg-open` receives the URL as a single argv entry
+            // schemes/args. Each opener receives the URL as a single argv entry
-            // (no shell), so there's no injection surface.
+            // (no shell), so there's no injection surface:
-            if (url.starts_with("http://") || url.starts_with("https://"))
+            //   - Unix: `xdg-open <url>`.
-                && let Err(e) = std::process::Command::new("xdg-open").arg(&url).spawn()
+            //   - Windows: `rundll32 url.dll,FileProtocolHandler <url>` — opens the
+            //     default browser without going through `cmd`/`start`, which would
+            //     otherwise re-parse `&` in query strings.
+            if url.starts_with("http://") || url.starts_with("https://") {
+                let spawned = {
+                    #[cfg(unix)]
                     {
+                        std::process::Command::new("xdg-open").arg(&url).spawn()
+                    }
+                    #[cfg(windows)]
+                    {
+                        std::process::Command::new("rundll32")
+                            .args(["url.dll,FileProtocolHandler", &url])
+                            .spawn()
+                    }
+                };
+                if let Err(e) = spawned {
                     crate::log_msg(&format!("Failed to open URL {url:?}: {e}"));
                 }
             }
+        }
         AppMessage::ToggleMicTest(enabled) => {
             state.mic_test_active = enabled;
             if !enabled {

src/audio/cpal_impl.rs

@@ -0,0 +1,67 @@
+//! Windows audio backend (cpal/WASAPI) — **Phase 0 stub**.
+//!
+//! This is a compile-and-run placeholder so the Windows build links and the app
+//! starts up (networking, UI, and text chat all functional) while the real
+//! capture/playback implementation lands in Phase 1. Every method satisfies the
+//! [`AudioBackend`] contract as a no-op: no microphone is captured and nothing is
+//! played. It deliberately pulls in no extra dependency — `cpal` is added only
+//! when the real implementation arrives.
+//!
+//! Phase 1 will replace this with cpal streams on the WASAPI host, mapping:
+//! - `start_capture` → input stream, f32→i16, mono 48 kHz, into `tx`;
+//! - `start_playback` → output stream draining a `ringbuf`, keeping `ring_fill`
+//!   updated so the existing hardware-clock pacing in the mixer keeps working;
+//! - `stop` → drop the streams.
+
+use std::sync::Arc;
+use std::sync::atomic::AtomicUsize;
+use std::sync::mpsc::{Receiver, Sender};
+
+use super::{AudioBackend, AudioError};
+
+/// No-op Windows audio backend (Phase 0). See module docs.
+pub struct CpalBackend;
+
+impl CpalBackend {
+    pub fn new() -> Self {
+        crate::log_msg("CpalBackend: Phase 0 stub active (no audio I/O yet)");
+        CpalBackend
+    }
+}
+
+impl Default for CpalBackend {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl AudioBackend for CpalBackend {
+    fn start_capture(
+        &self,
+        _tx: Sender<Vec<i16>>,
+        _target_node: Option<String>,
+    ) -> Result<(), AudioError> {
+        // No capture stream yet: dropping `_tx` simply means no samples are ever
+        // produced (silent mic), which is the intended Phase 0 behaviour.
+        crate::log_msg("CpalBackend::start_capture: not yet implemented (Phase 1) — capturing silence");
+        Ok(())
+    }
+
+    fn start_playback(
+        &self,
+        rx: Receiver<Vec<i16>>,
+        _target_node: Option<String>,
+        _ring_fill: Arc<AtomicUsize>,
+    ) -> Result<(), AudioError> {
+        // Drain and discard incoming audio on a detached thread so the mixer's
+        // producer never blocks or sees a closed channel. This keeps the rest of
+        // the pipeline running normally while output is silent.
+        std::thread::spawn(move || while rx.recv().is_ok() {});
+        crate::log_msg("CpalBackend::start_playback: not yet implemented (Phase 1) — discarding output");
+        Ok(())
+    }
+
+    fn stop(&self) -> Result<(), AudioError> {
+        Ok(())
+    }
+}

src/audio/mod.rs

@@ -62,6 +62,24 @@ pub mod gate;
 pub mod limiter;
 pub mod multitrack;
 pub mod pan;
+#[cfg(unix)]
 pub mod pipewire_impl;
+#[cfg(windows)]
+pub mod cpal_impl;
 pub mod pw_cli;
 pub mod recorder;
+
+/// The audio backend implementation for the current platform.
+///
+/// The whole app constructs and threads this alias (via
+/// `PlatformAudioBackend::new()`) rather than any concrete backend type, so
+/// platform selection lives entirely here. Both implementations satisfy the
+/// [`AudioBackend`] trait, which is the only interface the core talks to.
+///
+/// - Linux/Unix → PipeWire ([`pipewire_impl::PipeWireBackend`]).
+/// - Windows → cpal/WASAPI ([`cpal_impl::CpalBackend`]); a no-op stub until the
+///   Phase 1 capture/playback implementation lands.
+#[cfg(unix)]
+pub type PlatformAudioBackend = pipewire_impl::PipeWireBackend;
+#[cfg(windows)]
+pub type PlatformAudioBackend = cpal_impl::CpalBackend;

src/bin/audio_probe.rs

@@ -17,7 +17,22 @@
 //!
 //! Run:  cargo run --bin audio_probe -- [freq_hz] [seconds] [target_node]
 //!   e.g. cargo run --release --bin audio_probe -- 440 30
+//!
+//! This probe exercises the PipeWire backend directly, so it is a Unix-only tool.
+//! On non-Unix targets `main` is a stub that explains the limitation.
 
+#[cfg(unix)]
+fn main() {
+    unix_probe::run();
+}
+
+#[cfg(not(unix))]
+fn main() {
+    eprintln!("audio_probe is only supported on Unix builds (it drives the PipeWire backend directly).");
+}
+
+#[cfg(unix)]
+mod unix_probe {
     use std::io::{BufRead, BufReader, Seek, SeekFrom};
     use std::sync::Arc;
     use std::sync::atomic::AtomicUsize;
@@ -31,7 +46,7 @@ use peerspeak::core::jitter::FRAME_SAMPLES; // 960 mono frames = 20ms @ 48kHz
     const SAMPLE_RATE: f32 = 48_000.0;
 
     #[tokio::main]
-async fn main() {
+    pub async fn run() {
         let mut args = std::env::args().skip(1);
         let freq: f32 = args.next().and_then(|s| s.parse().ok()).unwrap_or(440.0);
         let secs: u64 = args.next().and_then(|s| s.parse().ok()).unwrap_or(30);
@@ -119,3 +134,4 @@ fn spawn_log_tailer() {
             }
         });
     }
+}

src/core/mod.rs

@@ -1,7 +1,7 @@
 pub mod messages;
 pub mod jitter;
 
-use crate::audio::{AudioBackend, pipewire_impl::PipeWireBackend};
+use crate::audio::{AudioBackend, PlatformAudioBackend};
 use crate::audio::eq::{Eq, EqSettings};
 use crate::codec::{AudioEncoder, opus_impl::OpusEncoder};
 use crate::core::jitter::{JitterBuffer, FRAME_SAMPLES};
@@ -237,7 +237,7 @@ fn run_mic_monitor(
 /// Stops a standalone mic monitor if one is running. MUST NOT be called while a
 /// room session is active — `backend.stop()` would also tear down the call's
 /// capture/playback. Monitor and session are mutually exclusive by construction.
-fn stop_mic_monitor(backend: &PipeWireBackend, monitor: Option<MicMonitor>) {
+fn stop_mic_monitor(backend: &PlatformAudioBackend, monitor: Option<MicMonitor>) {
     if let Some(m) = monitor {
         let _ = backend.stop();
         let _ = m.thread.join();
@@ -400,7 +400,7 @@ struct ActiveSession {
 }
 
 impl ActiveSession {
-    async fn shutdown(mut self, audio_backend: Arc<PipeWireBackend>) {
+    async fn shutdown(mut self, audio_backend: Arc<PlatformAudioBackend>) {
         crate::log_msg("ActiveSession::shutdown started");
         // Tear down any screen-share children first so the host stops streaming
         // promptly (kill_on_drop is the backstop, but kill explicitly so viewers
@@ -731,7 +731,7 @@ async fn run_core_loop(
     let known_peers: Arc<std::sync::Mutex<HashMap<String, HashMap<EndpointId, EndpointAddr>>>> =
         Arc::new(std::sync::Mutex::new(HashMap::new()));
 
-    let audio_backend = Arc::new(PipeWireBackend::new());
+    let audio_backend = Arc::new(PlatformAudioBackend::new());
 
     let is_muted = Arc::new(AtomicBool::new(false));
     let is_deafened = Arc::new(AtomicBool::new(false));

src/lib.rs

@@ -24,6 +24,9 @@ use std::path::{Path, PathBuf};
 use std::sync::OnceLock;
 
 const LOG_MAX_BYTES: u64 = 5 * 1024 * 1024;
+// Owner-only log permissions are a Unix concept (mode bits); on Windows the log
+// inherits the directory's default ACL. Only referenced under `cfg(unix)`.
+#[cfg(unix)]
 const LOG_MODE: u32 = 0o600;
 
 /// Resolves the log file path once: `$XDG_STATE_HOME/peerspeak/peerspeak.log`
@@ -84,8 +87,6 @@ fn prepare_log_file(path: &Path) -> std::io::Result<File> {
 }
 
 fn prepare_log_file_with_limit(path: &Path, max_bytes: u64) -> std::io::Result<File> {
-    use std::os::unix::fs::{OpenOptionsExt, PermissionsExt};
-
     if let Some(parent) = path.parent() {
         let _ = std::fs::create_dir_all(parent);
     }
@@ -98,12 +99,23 @@ fn prepare_log_file_with_limit(path: &Path, max_bytes: u64) -> std::io::Result<F
         }
     }
 
-    let file = std::fs::OpenOptions::new()
+    let mut opts = std::fs::OpenOptions::new();
-        .create(true)
+    opts.create(true).append(true);
-        .append(true)
+    // The log can carry capability-bearing values (redacted, but still): keep it
-        .mode(LOG_MODE)
+    // owner-only on Unix via the open mode. Windows has no mode bits; it inherits
-        .open(path)?;
+    // the directory ACL, so this hardening is Unix-only.
+    #[cfg(unix)]
+    {
+        use std::os::unix::fs::OpenOptionsExt;
+        opts.mode(LOG_MODE);
+    }
+    let file = opts.open(path)?;
+    #[cfg(unix)]
+    {
+        use std::os::unix::fs::PermissionsExt;
+        // Re-assert the mode in case the file pre-existed with looser perms.
         let _ = std::fs::set_permissions(path, std::fs::Permissions::from_mode(LOG_MODE));
+    }
     Ok(file)
 }
 
@@ -126,6 +138,7 @@ pub fn log_msg(msg: &str) {
 mod tests {
     use super::*;
     use std::io::Write;
+    #[cfg(unix)]
     use std::os::unix::fs::PermissionsExt;
 
     fn temp_log_dir() -> PathBuf {
@@ -145,6 +158,9 @@ mod tests {
         assert_eq!(redact_for_log("   "), "<redacted:empty>");
     }
 
+    // Owner-only log perms are a Unix concept; on Windows the file inherits the
+    // directory ACL and there's no mode to assert.
+    #[cfg(unix)]
     #[test]
     fn log_file_is_created_private() {
         let dir = temp_log_dir();