Karabiner parity: input source switching (select_input_source)

[malpern]

Summary

Karabiner-Elements supports select_input_source as an output action, allowing users to switch keyboard input methods (e.g., English ↔ Japanese) as part of a key mapping rule. Kanata has no native equivalent.

Current State

• Kanata: No native input source switching
• KeyPath: InputSourceDetector already monitors input source changes for the overlay (Japanese mode detection). Adjacent infrastructure exists.
• Karabiner converter: Rules using select_input_source are flagged as unconvertible (Tier 3)

Possible Approaches

1. TCP bridge: KeyPath's AppContextService pattern could be extended — detect input source change requests via push-msg and call macOS TISSelectInputSource API
2. Shell command fallback: Generate (cmd ...) actions that use macOS defaults write or third-party tools to switch input source
3. Upstream request: Request native input source support in Kanata

Impact

Primarily affects users of JIS keyboards and multi-language typists. Niche but important for Japanese/Chinese/Korean user segments.

Related

• Tracking issue: Tracking: 100% Karabiner conversion fidelity roadmap #213
• Feature matrix: docs/karabiner-converter-feature-matrix.md
• InputSourceDetector.swift — existing input source monitoring