Using a Mac for dev without changing your PC+Model M muscle memory

One basic requirement for me was keeping the pattern for CUA-style chords, i.e. Ctrl (on the PC keyboard) + C should do copy. The key on the Mac that (mostly) does this is Command, which is Super on an external 104-key keyboard, and nonexistent on a 101-key like the Model M. So Left Control should become Command.

Then, Left and Right Alt function as Left and Right Option for EurKEY (with Left inhibited by applications that use it). Right Control remains Control for applications that use it (except iTerm and Emacs, which we customise as below). macOS has some GUI controls for changing these mappings, but hidutil is more flexible. I generated the configuration using [Amar Syla's hidutil generator](https://hidutil-generator.netlify.app/), and as a personal preference also swapped Escape and Caps here. Here's the configuration (minus swapescape) in case the site is lost, to be put into ~/Library/LaunchAgents/com.local.KeyRemapping.plist:

 1<?xml version="1.0" encoding="UTF-8"?>
 2<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 3<plist version="1.0">
 4<dict>
 5    <key>Label</key>
 6    <string>com.local.KeyRemapping</string>
 7    <key>ProgramArguments</key>
 8    <array>
 9        <string>/usr/bin/hidutil</string>
10        <string>property</string>
11        <string>--set</string>
12        <string>{"UserKeyMapping":[
13            {
14              "HIDKeyboardModifierMappingSrc": 0x7000000E0,
15              "HIDKeyboardModifierMappingDst": 0x7000000E3
16            }
17        ]}</string>
18    </array>
19    <key>RunAtLoad</key>
20    <true/>
21</dict>
22</plist>

I also disabled Keyboard Shortcuts > Input Sources > Select the previous input source because I would frequently hit the chord without a need to escape from EurKEY.

In a shell, I still want Control + C to send SIGINT, so in Keys > Remap Modifiers, I set Left Command to Left Control and Right Control to Left Command for when command becomes necessary. Copying and pasting I want to do by Control + Shift + C/V, so these are set in Keys > Key Bindings, being the actions Copy Selection or Send ^C and Paste or Send ^V, respectively.

Finally, tell Emacs to interpret Command as Control. I also set Right Control as Super for when some rare chord requires it, and set Right Option to nil to maintain EurKEY functionality.

1(setq
2 mac-command-modifier 'control
3 mac-right-control-modifier 'super
4 mac-right-option-modifier nil)

I like a clean ~, and many applications will respect XDG_CONFIG_HOME et al. even though these variables are not standardised on macOS. Set system-wide environment variables like this in ~/Library/LaunchAgents/com.local.Env.plist. Spelling out the home directory (/Users/jakob in my case) is necessary AFAICT.

 1<?xml version="1.0" encoding="UTF-8"?>
 2<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 3<plist version="1.0">
 4<dict>
 5  <key>Label</key>
 6  <string>com.local.Env</string>
 7  <key>ProgramArguments</key>
 8  <array>
 9    <string>sh</string>
10    <string>-c</string>
11    <string>
12      launchctl setenv XDG_CACHE_HOME /Users/jakob/.cache && \
13      launchctl setenv XDG_CONFIG_HOME /Users/jakob/.config
14    </string>
15  </array>
16  <key>RunAtLoad</key>
17  <true/>
18</dict>
19</plist>

From this point on, you can use xdg-ninja for a cleaner home directory. Append to these launchctl commands to ensure a system-wide (i.e. including Emacs) setting.

I don't know enough about displays and their connections to explain the "why" or find a better solution, but color-on-color rendering was very jagged. Setting the connection to 8bit with BetterDisplay fixed this.