feat(findmy-tag): Find My タグの取得を10分ごとの LaunchAgent にする

nix/flake.nix

@@ -278,6 +278,7 @@
           ./home/macmini.nix
           ./home/macmini-backup.nix
           ./home/macmini-watchdog.nix
+          ./home/findmy-tag.nix # Find My タグの定期取得。ノートではなく常時稼働のこちらに置く
           # iMessage のブリッジ。他の mautrix は homeserver に置いてあるが、これだけ
           # chat.db と Messages.app が要るのでこの機械にしか置けない。
           ./home/macmini-imessage.nix

nix/home/findmy-tag.nix

@@ -0,0 +1,63 @@
+{ config, pkgs, ... }:
+# Polls Apple's Find My network for our own DIY tags (~/Developer/github.com/
+# gapul/generic-airtag) and appends what it gets to that repo's reports.db.
+#
+# Why the mini and not the laptop: a missed poll is a permanent hole (see below),
+# and a laptop with its lid shut misses every poll. Why not homeserver: the
+# anisette headers Apple demands come from AOSKit, which only exists on macOS —
+# a Linux host would need an anisette server fabricating a device identity,
+# which is the part of the usual setup this project exists to avoid. The mini
+# does not even need to be signed into iCloud; AOSKit answers for the machine,
+# not the user.
+#
+# The search-party token in auth.json is bound to the machine that obtained it:
+# copying it here from the laptop returns 401. Each machine logs in once.
+#
+# Why every 10 minutes and not, say, hourly: the fetch endpoint ignores the date
+# range in the request and returns only the newest handful of reports per key —
+# 8, measured on this account. Reports older than that stop being served long
+# before Apple's 7-day retention expires, so whatever a poll does not save is
+# lost for good. A tag being seen continuously produces roughly 8 reports per 15
+# minutes, which is what sets the interval.
+let
+  repo = "${config.home.homeDirectory}/Developer/github.com/gapul/generic-airtag";
+
+  # The devShell's python, rebuilt here so launchd does not have to evaluate a
+  # flake (and reach the network) every ten minutes. Keep in sync with the
+  # repo's flake.nix; srp/pbkdf2/pycryptodome are only needed by the vendored
+  # GSA login, which runs on the first login and never again.
+  python = pkgs.python3.withPackages (ps: [
+    ps.requests
+    ps.cryptography
+    ps.pyobjc-core # AOSKit, for anisette generated on this Mac
+    ps.pyobjc-framework-Cocoa
+    ps.srp
+    ps.pbkdf2
+    ps.pycryptodome
+  ]);
+
+  # Exits quietly when the repo is absent or nobody has logged in yet, so the
+  # agent is harmless on a machine where this project was never set up.
+  poll = pkgs.writeShellScript "findmy-tag-poll" ''
+    [ -d "${repo}" ] || exit 0
+    [ -r "${repo}/auth.json" ] || exit 0
+    cd "${repo}" && exec ${python}/bin/python src/fetch.py
+  '';
+in
+{
+  launchd.agents.findmy-tag = {
+    enable = true;
+    config = {
+      ProgramArguments = [ "${poll}" ];
+      StartInterval = 600;
+      # Nothing backfills a gap, so poll immediately after a reboot rather than
+      # waiting out the first interval.
+      RunAtLoad = true;
+      ProcessType = "Background";
+      # No log rotation: the script prints one line per run. Errors are the only
+      # reason to look, and silence here means the agent never ran at all.
+      StandardErrorPath = "${config.home.homeDirectory}/Library/Logs/findmy-tag.log";
+      StandardOutPath = "${config.home.homeDirectory}/Library/Logs/findmy-tag.log";
+    };
+  };
+}