fix(box): login agents on a Mac run as interactive work, not background

cmd/berth/agentprocess.go

@@ -97,6 +97,11 @@ func runAgent(l laptop) error {
 	ctx, stop := signalContext()
 	defer stop()
 	cfg := agent.Config{Dir: l.dir, Socket: l.socket()}
+	if spec, err := agentService(l); err == nil {
+		if _, err := service.Migrate(spec); err != nil {
+			fmt.Fprintf(os.Stderr, "berth agent: updating its service: %v\n", err)
+		}
+	}
 	// The app's Copy diagnostics shows what `berth doctor` would (GET /v1/doctor).
 	cfg.Doctor = func(ctx context.Context) []doctor.Check { return laptopChecks(ctx, l) }
 	// A second agent (a test, a throwaway home) needs its own ports.

cmd/berthd/main.go

@@ -268,6 +268,9 @@ func serve(b boxHome, args []string) error {
 		// A plist from an older install gives launchd's bare PATH, without
 		// Homebrew's tmux; find it anyway.
 		service.AugmentPATH()
+		if _, err := service.Migrate(daemonService(b, "")); err != nil {
+			fmt.Fprintf(os.Stderr, "berthd: updating its launchd plist: %v\n", err)
+		}
 	}
 	utf8Locale()
 	if *listen == "" {

docs/changelog.mdx

@@ -10,6 +10,13 @@ upgrades with `berth upgrade BOX`, or by running the
 again.
 
 ## Unreleased
+- **Agents on a Mac run at full speed.** Shipyard's login agents (the
+  Mac app's agent, and `berthd` on a Mac box) used to ask macOS to run
+  them as background work, which slows their CPU and disk, and with them
+  every agent and build they start. They now run as interactive work.
+  Updating the app applies it to this Mac right away. A Mac box updated
+  with **Update all** gets it the next time it restarts or you log in
+  there; running the install command again applies it at once.
 - **Back and Forward, as in a browser.** The arrows at the top of the
   sidebar, ⌘[ and ⌘] (also in the Go menu and ⌘K), and a mouse's back and
   forward buttons take you through the places you've been: a page such as
@@ -23,7 +30,6 @@ again.
   a menu to add a project or a box. Those stay on the rail's own + and
   the boxes row at the bottom of the sidebar.
 
-
 ## v0.3.29
 
 - **Removing a worktree no longer asks first.** Remove worktree in the

internal/service/service.go

@@ -152,7 +152,7 @@ func Render(s Spec) ([]byte, error) {
 <key>RunAtLoad</key><true/>
 <key>KeepAlive</key><dict><key>SuccessfulExit</key><false/></dict>
 <key>ThrottleInterval</key><integer>5</integer>
-<key>ProcessType</key><string>Background</string>
+<key>ProcessType</key><string>Interactive</string>
 `)
 		if s.KeepChildren {
 			b.WriteString("<key>AbandonProcessGroup</key><true/>\n")
@@ -191,6 +191,44 @@ func Render(s Spec) ([]byte, error) {
 
 func esc(s string) string { return html.EscapeString(s) }
 
+// Lines older releases wrote, and what Render writes in their place now.
+var migrations = []struct{ old, new string }{
+	// Background throttles the CPU and disk of the service and of everything
+	// it starts, agents and their builds included, as they inherit it.
+	{"<key>ProcessType</key><string>Background</string>\n", "<key>ProcessType</key><string>Interactive</string>\n"},
+}
+
+// Migrate brings the unit an older release wrote for s up to date in place,
+// so it is Installed again, and says whether it changed it. A unit for
+// another program or BERTH_HOME (another install, a test's) is left alone.
+// Only the file changes: launchd reads it at the next load (a login, a
+// reinstall), and a running service is never restarted for it. A berthd
+// upgraded from the app swaps its binary without reinstalling, so this is
+// how its plist catches up.
+func Migrate(s Spec) (bool, error) {
+	u, ok, err := Read(s.Name)
+	if err != nil || !ok || u.Program != s.Program || u.Env["BERTH_HOME"] != s.Env["BERTH_HOME"] {
+		return false, err
+	}
+	have, err := os.ReadFile(u.Path)
+	if err != nil {
+		return false, err
+	}
+	path := u.Path
+	data := string(have)
+	for _, m := range migrations {
+		data = strings.ReplaceAll(data, m.old, m.new)
+	}
+	if data == string(have) {
+		return false, nil
+	}
+	tmp := path + ".tmp"
+	if err := os.WriteFile(tmp, []byte(data), 0o644); err != nil {
+		return false, err
+	}
+	return true, os.Rename(tmp, path)
+}
+
 func systemdArgs(args []string) string {
 	quoted := make([]string, len(args))
 	for i, a := range args {

internal/service/service_test.go

@@ -44,6 +44,7 @@ func TestUnitsRestartOnlyAfterFailure(t *testing.T) {
 		"<key>RunAtLoad</key><true/>",
 		"<string>/opt/berth/bin/berth</string>\n<string>agent</string>",
 		"<key>BERTH_HOME</key><string>/Users/alex/Library/Application Support/berth</string>",
+		"<key>ProcessType</key><string>Interactive</string>",
 	} {
 		if !strings.Contains(string(plist), want) {
 			t.Errorf("plist missing %q:\n%s", want, plist)
@@ -327,3 +328,44 @@ func TestPreflightOnAMacNeedsALoginSession(t *testing.T) {
 		t.Errorf("without a GUI session: %v", err)
 	}
 }
+
+func TestMigrateBringsAnOlderPlistUpToDateWithoutReloading(t *testing.T) {
+	home, calls := stub(t, "darwin")
+	plist, err := Render(spec)
+	if err != nil {
+		t.Fatal(err)
+	}
+	old := strings.Replace(string(plist), "<string>Interactive</string>", "<string>Background</string>", 1)
+	path := filepath.Join(home, "Library", "LaunchAgents", spec.Name+".plist")
+	os.MkdirAll(filepath.Dir(path), 0o755)
+	os.WriteFile(path, []byte(old), 0o644)
+
+	other := spec
+	other.Program = "/somewhere/else/berth"
+	if changed, err := Migrate(other); err != nil || changed {
+		t.Fatalf("another program's plist: changed=%v err=%v", changed, err)
+	}
+	if Installed(spec) {
+		t.Fatal("an older plist counts as installed before Migrate")
+	}
+	if changed, err := Migrate(spec); err != nil || !changed {
+		t.Fatalf("changed=%v err=%v", changed, err)
+	}
+	if !Installed(spec) {
+		data, _ := os.ReadFile(path)
+		t.Fatalf("after Migrate the plist is not what Render writes:\n%s", data)
+	}
+	if changed, err := Migrate(spec); err != nil || changed {
+		t.Fatalf("a second Migrate: changed=%v err=%v", changed, err)
+	}
+	if len(*calls) != 0 {
+		t.Fatalf("Migrate ran %v; it must not reload the service", *calls)
+	}
+}
+
+func TestMigrateWithoutAPlist(t *testing.T) {
+	stub(t, "darwin")
+	if changed, err := Migrate(spec); err != nil || changed {
+		t.Fatalf("changed=%v err=%v", changed, err)
+	}
+}