Support ALSA plugin devices (dmix) for dual mono setups

[balloob]

Summary

• Refactor audio device handling to new audio_devices.py
• Allow --audio-device to accept raw ALSA device names (e.g., dmixer, olohuone) in addition to numeric indices and name prefixes
• When a string doesn't match any PortAudio-enumerated device, it's validated and passed directly to sounddevice, letting PortAudio's ALSA backend open named plugin devices like dmix
• This enables multiple daemon instances to share a single sound card via dmix for multi-room dual mono setups

Root cause

PortAudio only enumerates hardware ALSA devices, not plugin devices (dmix, plug, etc.). When one daemon opens a hardware device via PortAudio, it acquires exclusive access, preventing the second daemon from even enumerating devices — sounddevice.query_devices() returns an empty list. ALSA dmix is designed for device sharing, but PortAudio bypasses it by opening the raw hardware directly.

Changes

• sendspin/audio.py: Extended AudioDevice with optional alsa_device_name field and device_id property; updated type signatures to accept int | str | None for device parameters
• sendspin/cli.py: Added _try_alsa_device() fallback in device resolution; updated help text and --list-audio-devices output with ALSA hint on Linux
• sendspin/tui/app.py and sendspin/daemon/daemon.py: Use device_id instead of index for format detection
• README.md: Documented ALSA device name usage with dual mono example

Usage

# Room 1: left channel via dmix
sendspin daemon --name "Living Room" --audio-device olohuone

# Room 2: right channel via dmix  
sendspin daemon --name "Kitchen" --audio-device keittio

Test plan

• Verify --list-audio-devices still works and shows ALSA hint on Linux
• Verify numeric device index selection still works (--audio-device 0)
• Verify name prefix selection still works (--audio-device "MacBook")
• Verify raw ALSA device name works on a Linux system with dmix configured
• Verify two daemons can run simultaneously with different dmix devices
• Verify invalid ALSA device name gives a clear error message

Fixes #58

https://claude.ai/code/session_01G86ZS2aLyMqx3rDwQnsaUS

[Copilot]

Pull request overview

This PR extends Sendspin’s audio-device selection to support raw ALSA plugin device names (e.g., dmix/custom pcm.* names) in addition to PortAudio-enumerated indices and name prefixes, enabling dual-mono/multi-daemon setups on a single sound card via dmix.

Changes:

• Add alsa_device_name + device_id to AudioDevice, and widen format-probing/validation APIs to accept int | str | None.
• Update CLI audio-device resolution to fall back to opening a raw ALSA device name when enumeration doesn’t match, and improve Linux help/output hints.
• Switch TUI/daemon format detection to use device_id rather than assuming a numeric index; document usage in README.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
sendspin/audio.py	Adds alsa_device_name and device_id; updates sounddevice-related function signatures and stream creation to accept string device IDs.
sendspin/cli.py	Adds ALSA-name fallback resolution for --audio-device, updates help text, and adds Linux-specific guidance to --list-audio-devices.
sendspin/tui/app.py	Uses device_id for supported-format detection.
sendspin/daemon/daemon.py	Uses device_id for supported-format detection.
README.md	Documents selecting raw ALSA device names and provides a dual-mono example.

Comments suppressed due to low confidence (1)

sendspin/audio.py:473

• The log message ends with device=%s but passes the entire AudioDevice object, which will produce a verbose dataclass repr (and for ALSA-named devices may include index=None). Consider logging device.device_id instead for a stable, user-focused identifier.

        logger.info(
            "Audio stream configured: codec=%s, sample_rate=%d, channels=%d, bit_depth=%d, blocksize=%d, latency=high, device=%s",
            audio_format.codec.value,
            pcm_format.sample_rate,
            pcm_format.channels,

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