Stage 6b — Volume and Brightness Service Adapters

Why this stage exists

Stage 6a proved the patin::service::Provider + opt-in-crate pattern with battery, which polls a real D-Bus service (UPower). Volume and brightness were the two demo fixtures still left as subprocess/sysfs code inline in examples/demo_bar/services.rs.

Neither has a real D-Bus service to key a crate name off the way UPower did for battery: Linux audio has no universal standard D-Bus volume interface, and systemd-logind only exposes a SetBrightness method, not a readable one. So this stage names by domain concept instead of mechanism — patin-service-volume and patin-service-brightness — and is otherwise a mechanical port: the existing, already-working subprocess/sysfs logic moved verbatim into two new crates implementing Provider, restructuring their return values from pre-formatted strings into typed snapshots (matching BatterySnapshot’s shape), with formatting left to the demo. No new external dependencies, no calloop changes — same poll-once-per-second model as battery.

New crate: `patin-service-volume`

Ports read_volume/read_wpctl_volume/read_pactl_volume/ parse_wpctl_volume from the demo, returning VolumeSnapshot { percentage, muted } instead of a pre-formatted string. The percentage is no longer discarded when muted — the demo’s formatter chooses to still show "VOL MUTE" for now, but the data is available. Depends only on patin (for Provider); Command handling is all std.

New crate: `patin-service-brightness`

Ports read_brightness/brightness_label/read_trimmed verbatim, returning BrightnessSnapshot { percentage }. Same no-external-dependency shape as the volume crate.

Demo integration

examples/demo_bar/services.rs is now composition-and-formatting only: SystemStatus holds all three providers (BatteryProvider, VolumeProvider, BacklightProvider); poll calls each .poll() and maps through format_battery/format_volume/format_brightness to rebuild the same "BAT n%[+]" / "VOL n%" / "VOL MUTE" / "BRI n%" strings scene.rs already expected — scene.rs itself is unchanged. Root Cargo.toml gained both crates under [workspace] members and [dev-dependencies].

Documentation

docs/status-services.md was retitled from “Demo Status Fixtures” to “Status Providers” and rewritten: none of the three are demo-only fixtures anymore, only their composition into StatusSnapshot is. README.md and docs/architecture.md were updated to list all three adapter crates and drop the now-inaccurate “provisional audio and brightness providers are used by the demo only” framing.

Verification

Verified on 30 July 2026:

$ cargo fmt --all -- --check
(no output)

$ cargo test --workspace --all-targets
10 tests across 4 crates, all passed:
  patin: 5
  examples/demo_bar: 2
  patin-service-brightness: 1 (computes_brightness_and_rejects_zero_maximum)
  patin-service-upower: 1 (poll_without_a_system_bus_returns_none)
  patin-service-volume: 1 (parses_wpctl_volume_and_mute_state)

$ cargo clippy --workspace --all-targets --all-features -- -D warnings
Finished `dev` profile [unoptimized + debuginfo] target(s), no warnings

$ cargo run --example demo_bar (timeout 5s, this sandbox: no upowerd)
demo_bar: status providers: battery=unavailable, volume=VOL MUTE, brightness=BRI 71%
patin: connected; waiting for the compositor to configure the bar

$ mdbook build
 INFO Book building has started
 INFO Running the html backend
 INFO HTML book written to `/home/vdzee/proj/patin/book`

$ git diff --check
(no output, exit 0)

FP5 end-to-end confirmation

Verified on the FP5 the same day, same round-trip as stage 6a: working tree copied over with tar piped over SSH, built natively (cargo build --release --locked --example demo_bar, ~6s — fast, since zbus and its transitive deps were already cached from stage 6a and neither new crate adds an external dependency), then installed and relaunched as a transient systemd user unit (plain backgrounded SSH processes don’t survive the PAM session tearing down, per stage 6a):

systemd-run --user --unit=patin-demo --collect \
  --setenv=XDG_RUNTIME_DIR=/run/user/10000 \
  --setenv=WAYLAND_DISPLAY=wayland-0 \
  -- /home/sn3rt/.local/bin/patin

demo_bar: status providers: battery=BAT 66%, volume=VOL 8%, brightness=BRI 40%
patin: connected; waiting for the compositor to configure the bar

All three readings are real, not unavailable/degraded — patin-service-volume and patin-service-brightness work end to end against the FP5’s real wpctl/sysfs, alongside the already-proven UPower battery adapter.

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