Phase 3 — bring up the daemon end-to-end through six checkpoints:
3a Module skeleton (error, profile, routing, runtime, pw/*)
3b Pure routing engine + 13 tests (no PipeWire dep)
3c PwContext: main loop, sigprocmask-block SIGTERM/SIGINT before
add_signal_local so signalfd actually picks them up
3d headroom-processed virtual sink via the adapter factory with
factory.name=support.null-audio-sink
3e Filter: two pw_streams (capture from monitor / playback to real
sink) with an rtrb SPSC ring between them. DSP chain
(Compressor → two-tier Limiter) runs in the playback callback.
Allocation-free; #![forbid(unsafe_code)] preserved via
bytemuck::try_cast_slice for the byte↔f32 reinterpretation.
3f Registry watcher binds the default metadata, evaluates new
Stream/Output/Audio nodes against profile rules, writes
target.object for processed routes. Self-stream guard skips
anything whose node.name starts with 'headroom-filter'.
Workspace deps added: pipewire = { features = ["v0_3_44"] } for the
modern TARGET_OBJECT key, libspa, rtrb, nix (sigprocmask), bytemuck.
Tests: 65 passing (28 dsp, 20 ipc, 4 client, 13 core). Clippy clean
at default level under -D warnings.
PLAN.md §5 renumbered to fix stale subsection labels (was 4.1–4.4
from before the per-app insertion).
Known limitations punted to Phase 4 (documented in commit history
and team memory):
- WirePlumber doesn't always honor late target.object writes once
a stream is already linked (timing race).
- preferred_real_sink dynamic tracking stubbed.
- No auto-promote of headroom-processed to system default.
- application.process.binary occasionally arrives in late metadata
updates after the global registers; routing logs show '?' until
we add a re-read.
