feat(linux): add systemd --user backend to 4 scheduler installers

[takanorinishida]

What's broken

DerivedSync.ts / CommitmentSweep.ts / UsageAggregator.ts / CodexUpdate.ts have no macOS dependency in their service bodies (they're plain bun scripts), but their installers only know how to write a launchd plist — so none of the 4 can be scheduled on Linux.

DerivedSync in particular has real user-visible impact: it's what keeps PRINCIPAL_TELOS.md (imported by CLAUDE.md) and LIFEOS_STATE.json (read by the statusline rings) in sync with hand-edited TELOS files. Without it, those two files silently go stale after every TELOS edit.

Fix

Follows the process.platform dispatch pattern InstallWorkSweep.ts established (#1692, closed/ported): darwin path untouched, linux path materializes a systemd --user unit pair instead of a plist.

• derivedsync: WatchPaths (7 dirs) + RunAtLoad → .path unit (PathModified x7) + .service (oneshot); the service is started once at install time to match RunAtLoad's "fire once when loaded" behavior
• commitmentsweep: StartCalendarInterval 07:00 → .timer (OnCalendar, Persistent=true) + .service
• usage-aggregator: StartCalendarInterval 03:30 + RunAtLoad → .timer (OnCalendar + OnBootSec=2min) + .service
• codexupdate: StartCalendarInterval 04:00, no RunAtLoad → .timer (OnCalendar only) + .service

ThrottleInterval becomes StartLimitIntervalSec/StartLimitBurst on the .service (not on derivedsync's .path — TriggerLimitIntervalSec needs systemd 255+, unavailable on e.g. Debian 12's 252).

InstallCommitmentSweep.ts's darwin plist hardcodes /opt/homebrew/bin/bun (no detectBun()) — left untouched. Only the new linux path calls a newly-added detectBun() to resolve {{BUN}} in the systemd templates.

Also fixes BackgroundServices.md's now-inaccurate "macOS-only" claim in the Fresh Install section.

Why this doesn't change macOS behavior

Every deletion in this diff is either a const moved a few lines up (LABEL, STATE_DIR, COMMAND_TIMEOUT_MS — same value, same file, just relocated next to the other platform-specific paths) or a dispatch line that now ternaries into the same original function, renamed *Darwin with its body byte-for-byte unchanged. No darwin behavior is touched.

Verification

Tested end-to-end on Ubuntu 24.04 / systemd 255:

• systemd-analyze --user verify passes clean on all 8 new units
• DerivedSync: install → .path unit active → touching TELOS.md fired a targeted re-run (confirmed via the tool's own derived-sync.jsonl log — only the actions tied to the changed file ran) → PRINCIPAL_TELOS.md regenerated. Re-running install is idempotent. --uninstall removes both units cleanly.
• UsageAggregator: install → the boot-equivalent run fired immediately, exited 0, wrote usage-daily.jsonl. Timer correctly queued for the next 03:30.
• CommitmentSweep: install → timer correctly queued for the next 07:00; service not run (matches RunAtLoad false).
• CodexUpdate: timer registered for 04:00; service deliberately left un-started in this test (it has global-install side effects) — systemctl --user is-active confirms inactive.

Unrelated pre-existing bug found during verification, not fixed here (out of scope — it's in DerivedSync.ts's own logic, not the installer/scheduler): DeriveDenyHashes.ts fails with ENOENT because ~/.claude/skills/_LIFEOS/ doesn't exist on this host. Would fail identically under launchd.

Related: #1692 (WorkSweep systemd backend, same pattern, ported).

🤖 Generated with Claude Code