Export and import settings and layout as a file

[sumeet-bansal]

Problem

There is no supported way to save an OpenUsage configuration to a file, carry it to a second
Mac, or keep it under version control. Every setting and the whole Customize layout live only in
the app's UserDefaults domain, com.robinebers.openusage, alongside runtime state: provider
snapshots that are rewritten on every refresh, the account registry, the iCloud device id, the
shell-environment snapshot, and Sparkle's update state. The existing mechanisms do not cover it:

• iCloud sync covers history only, by design (docs/icloud-sync.md).
• The plist is binary, and about 80% of it is the snapshot cache, so it changes every five
  minutes.
• Symlinking the plist into a dotfiles repo does not work: cfprefsd refuses to write a domain
  whose plist is a symlink ("Could not write domain"), so the app can no longer save settings.

"Reset All Settings" (#602) exists, but there is no counterpart that saves a configuration and
restores it.

Proposed Solution

A JSON export and import of user-chosen configuration only, reachable from the openusage CLI
(openusage settings export writing to stdout, openusage settings import <file>) and, if it
fits the Settings screen, as buttons beside Reset All Settings.

In scope:

• Customize layout and metric order
• Menu-bar pins and style
• Expanded metrics
• Enabled providers
• Appearance, density, and meter style
• Pacing
• Notification toggles
• Total-spend settings
• Update preferences

Out of scope, as refetchable or machine-specific:

• Provider snapshots
• The account registry
• The iCloud device id
• The shell-environment snapshot
• Sparkle timestamps

Import merges over the current domain and reloads the layout, the way defaults import merges
keys, so a partial file only touches the keys it names.

Alternatives Considered

• iCloud sync: history only, and I would want the layout in git rather than in iCloud anyway.
• Symlinking the preferences plist: cfprefsd rejects writes through a symlink (tested on
  macOS 26.6).
• defaults export filtered to an allowlist, then defaults import: this is what I do today.
  It works (21 keys; the three Data-typed layout keys hold JSON and decode cleanly), but it
  depends on internal key names that carry schema versions (openusage.layout.v1,
  openusage.providerSnapshots.v9), so it breaks silently whenever those names change. A
  first-party export is the stable version of the same allowlist.

Additional Context

OpenUsage 0.7.x on macOS 26.6, Apple Silicon. The allowlist above is the set of keys that
survived a capture, import, restart, and recapture round trip byte-for-byte; I can share it
if it helps scope the export.