fix: volume percentage briefly reverting after user change

[1knth]

What

Fixes the volume percentage briefly flashing back to an old value after the user changes it, especially noticeable when spamming volume up/down.

Why

Spotify's API returns playback state on a polling interval. After a local volume change, the next poll response can still carry the old volume. Previously this would overwrite the user's intended value in the UI before the API caught up.

Before

UI read volume directly from the API response — no awareness of user intent:

// src/tui/ui/player.rs:539
current_playback_context.device.volume_percent.unwrap_or(0)

increase_volume calculated from the (potentially stale) API value:

// src/core/app.rs:1608
pub fn increase_volume(&mut self) {
    if let Some(context) = self.current_playback_context.clone() {
        let current_volume = context.device.volume_percent.unwrap_or(0) as u8;
        // ...
        self.dispatch(IoEvent::ChangeVolume(next_volume));
    }
}

change_volume just updated context directly — no coalescing or stale-response protection:

// src/infra/network/playback.rs:724
Ok(_) => {
    let mut app = self.app.lock().await;
    if let Some(ctx) = &mut app.current_playback_context {
        ctx.device.volume_percent = Some(volume.into());
    }
}

VolumeChanged handler blindly overwrote local state on every event:

// src/main.rs:1953
if let Some(ref mut ctx) = app.current_playback_context {
    ctx.device.volume_percent = Some(volume_percent as u32);
}
app.user_config.behavior.volume_percent = volume_percent.min(100);
let _ = app.user_config.save_config();
After
New desired_volume() returns user's intent, falling back to API:
pub fn desired_volume(&self) -> u32 {
    if let Some(pending) = self.pending_volume {
        return pending as u32;
    }
    self.current_playback_context.as_ref()
        .and_then(|c| c.device.volume_percent).unwrap_or(0)
}

UI and volume-adjust functions use desired_volume() — always shows user's last input:

// UI: src/tui/ui/player.rs
app.desired_volume()
// increase_volume / decrease_volume: src/core/app.rs
let current_volume = self.desired_volume() as u8;
self.pending_volume = Some(next_volume);

change_volume coalesces rapid presses and keeps pending_volume alive until the API confirms:

// src/infra/network/playback.rs
Ok(_) => {
    let mut app = self.app.lock().await;
    if let Some(ctx) = &mut app.current_playback_context {
        ctx.device.volume_percent = Some(volume.into());
    }
    app.is_volume_change_in_flight = false;
    app.last_dispatched_volume = Some(volume);
    // Keep pending_volume set — cleared when API confirms the value matches
}

API poll checks if Spotify caught up — stale responses are ignored:

// src/infra/network/playback.rs — get_current_playback
if let Some(pending) = app.pending_volume {
    let api_vol = c.device.volume_percent.unwrap_or(0) as u8;
    if api_vol == pending {
        app.pending_volume = None;
        app.last_dispatched_volume = None;
    } else {
        // API hasn't caught up yet — keep showing the user's intended value
        c.device.volume_percent = ctx.device.volume_percent;
    }
}

VolumeChanged handler skips overwrite when user has a pending change, still persists config:

// src/main.rs
if let Some(pending) = app.pending_volume {
    if volume_percent == pending {
        app.pending_volume = None;
        app.last_dispatched_volume = None;
    }
    app.user_config.behavior.volume_percent = volume_percent.min(100);
    let _ = app.user_config.save_config();
} else {
    if let Some(ref mut ctx) = app.current_playback_context {
        ctx.device.volume_percent = Some(volume_percent as u32);
    }
    app.user_config.behavior.volume_percent = volume_percent.min(100);
    let _ = app.user_config.save_config();
}

Files changed
- src/core/app.rs — pending_volume, last_dispatched_volume, is_volume_change_in_flight fields; desired_volume() helper; updated increase_volume/decrease_volume/flush_pending_volume
- src/infra/network/playback.rs — change_volume keeps pending_volume on success; get_current_playback confirms or rejects stale responses
- src/main.rs — VolumeChanged handler checks native confirmation while preserving config persistence
- src/tui/ui/player.rs — UI uses app.desired_volume()
- CHANGELOG.md — added unreleased fix entry

Testing:

• cargo fmt --all ✓
• cargo clippy --no-default-features --features telemetry -- -D warnings ✓
• cargo test --no-default-features --features telemetry ✓ (147 tests)
• Manual testing on macOS with native streaming — rapid volume clicks no longer glitch

[1knth]

my agent hallucinated initial pr message. sorry!