Add adjustable audio ducking during recording (closes #683)

[dhryniewicz]

Summary

Implements the feature requested in #683: a slider for adjustable volume reduction (ducking) during recording, instead of only binary mute/unmute. Users who listen to background music or video while dictating can now keep audio audible at a reduced level rather than silencing it completely.

Behavior

• New setting Ducking Amount (0–100%, step 5) lives inside the existing Mute Audio While Recording expandable row.
• Default is 100%, which preserves the previous full-mute behavior — no migration needed for existing users.
• 100% uses the original kAudioDevicePropertyMute path, so the macOS volume slider keeps its visual position (just shows the muted icon), and existing user-mute detection still applies.
• <100% captures the current output volume, reduces it via kAudioDevicePropertyVolumeScalar to currentVolume × (100 − percent) / 100, and restores the original volume on stop (respecting the existing audioResumptionDelay).
• 0% is treated as a no-op while the toggle is on.

Implementation

• MediaController.swift: added audioDuckingPercent (UserDefaults-backed), a DuckingMode enum to track which path was used (mute vs. volume scalar) for correct restore, and getSystemVolume() / setSystemVolume() helpers mirroring the existing CoreAudio mute helpers.
• SettingsView.swift: added a Slider + percentage label + InfoTip inside the existing Mute row.
• AppDefaults.swift: registered audioDuckingPercent: 100 so existing users continue to get full mute.

The unmuteSystemAudio() cancellation/generation logic is preserved; volume restore is gated by the same muteGeneration check so quickly-retriggered recordings don't race.

Test plan

• make local — builds cleanly with no new warnings
• Manual: 100% (default) — system audio fully mutes during recording, restores after (no regression vs. main)
• Manual: 50% — music continues at reduced volume during recording, restores to original level after stop
• Manual: 0% — no audio change while toggle is on
• Manual: with audioResumptionDelay > 0, volume restore is correctly delayed

[cubic-dev-ai]

1 issue found across 3 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="VoiceInk/MediaController.swift">

<violation number="1" location="VoiceInk/MediaController.swift:51">
P2: `activeDuckingMode` can stay stale across a mute cycle, so a later stop may restore an old saved volume even when the current recording never ducked audio.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

1 issue found across 1 file (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="VoiceInk/MediaController.swift">

<violation number="1" location="VoiceInk/MediaController.swift:44">
P1: Clearing `activeDuckingMode` before a new ducking action succeeds can discard the only restore state after canceling the previous pending unmute, leaving system audio stuck in the prior muted/ducked state.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

1 issue found across 1 file (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="VoiceInk/MediaController.swift">

<violation number="1" location="VoiceInk/MediaController.swift:109">
P2: Clears ducking ownership/state even if the immediate restore fails, so a cancelled prior cycle can leave audio modified with no saved baseline for the next cycle.</violation>
</file>

_{Tip: Review your code locally with the cubic CLI to iterate faster.}

[cubic-dev-ai]

1 issue found across 1 file (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="VoiceInk/MediaController.swift">

<violation number="1" location="VoiceInk/MediaController.swift:102">
P1: Overwriting an unresolved `.mute` restore with `.volume` loses the fact that the device still needs an unmute, which can leave system audio muted after recording stops.</violation>
</file>

_{Tip: Review your code locally with the cubic CLI to iterate faster.}