cronr: recurring/one-shot jobs as systemd user timers

add (schedule validated by systemd-analyze, units + script printed),
list (next elapse + last result), run, logs, rm. Command stored as a
script so quoting never meets ExecStart; PATH includes ~/.local/bin
so agent tools resolve. cronr-* namespace guards foreign units.
Smoked live: add -> run -> journal -> rm. Spec: doc/tool-parity.md 3.1.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011KikHkfCiC3yELbsMN8fT9

cronr/unit/unit.go

@@ -0,0 +1,96 @@
+// Package unit generates the systemd user units cronr manages. Pure
+// text generation — systemd does the scheduling, cronr owns no daemon.
+package unit
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+)
+
+// Prefix namespaces everything cronr creates so list/rm can never
+// touch units it does not own.
+const Prefix = "cronr-"
+
+var nameRe = regexp.MustCompile(`^[a-zA-Z0-9][a-zA-Z0-9_-]*$`)
+
+// ValidName reports whether a job name is safe for unit/file names.
+func ValidName(name string) bool {
+	return len(name) <= 64 && nameRe.MatchString(name)
+}
+
+// Script wraps the job command in an executable shell script — the
+// unit ExecStart points here, so arbitrary quoting in the command
+// never meets systemd's ExecStart parsing.
+func Script(cmd string) string {
+	return "#!/bin/sh\n# generated by cronr - the job's command lives here so systemd\n# unit quoting never mangles it\n" + cmd + "\n"
+}
+
+// Service renders the .service unit. PATH gets ~/.local/bin first so
+// jobs can call agent tools (notifyr, svgc, agy, ...) like a login
+// shell would.
+func Service(name, scriptPath string) string {
+	return fmt.Sprintf(`[Unit]
+Description=cronr job %s
+
+[Service]
+Type=oneshot
+Environment=PATH=%%h/.local/bin:/usr/local/bin:/usr/bin:/bin
+ExecStart=/bin/sh %s
+`, name, scriptPath)
+}
+
+// Timer renders the .timer unit. Recurring jobs get Persistent=true
+// (a missed run fires at next boot/login); one-shots do not.
+func Timer(name, calendarSpec string, oneshot bool) string {
+	persistent := "true"
+	if oneshot {
+		persistent = "false"
+	}
+	return fmt.Sprintf(`[Unit]
+Description=cronr timer for %s
+
+[Timer]
+OnCalendar=%s
+Persistent=%s
+
+[Install]
+WantedBy=timers.target
+`, name, calendarSpec, persistent)
+}
+
+// UnitNames returns the service and timer unit names for a job.
+func UnitNames(name string) (service, timer string) {
+	return Prefix + name + ".service", Prefix + name + ".timer"
+}
+
+// JobName extracts the job name from a cronr unit filename, or ""
+// if the filename is not cronr's.
+func JobName(unitFile string) string {
+	base := unitFile
+	if i := strings.LastIndex(base, "/"); i >= 0 {
+		base = base[i+1:]
+	}
+	if !strings.HasPrefix(base, Prefix) {
+		return ""
+	}
+	base = strings.TrimPrefix(base, Prefix)
+	for _, suffix := range []string{".timer", ".service"} {
+		if strings.HasSuffix(base, suffix) {
+			return strings.TrimSuffix(base, suffix)
+		}
+	}
+	return ""
+}
+
+// AtToCalendar converts "YYYY-MM-DD HH:MM" (or with seconds) to a
+// systemd calendar spec for one-shot jobs. systemd accepts the format
+// as-is; this just validates the shape early with a helpful error.
+var atRe = regexp.MustCompile(`^\d{4}-\d{2}-\d{2} \d{2}:\d{2}(:\d{2})?$`)
+
+func AtToCalendar(at string) (string, error) {
+	if !atRe.MatchString(at) {
+		return "", fmt.Errorf("--at must be \"YYYY-MM-DD HH:MM[:SS]\", got %q", at)
+	}
+	return at, nil
+}