One kind for the module's own code, with three modes

The first cut of this added a `daemon` for the long-running case alone. That
would have meant a new vocabulary entry for each of the others — a scheduled
task, a run-once migration, a health check — when they are one thing run at
different cadences. That is a field, not four entries in a vocabulary where every
entry widens what a compromised control plane can express.

So it mirrors a container exactly, because it IS a container's twin: the same
intent, hosted by the machine's own supervisor instead of a runtime. Stays up,
runs once, or runs on a schedule.

Tools, hooks and event consumers are not further modes. They are loaded by a tool
host, which is itself a process that stays up — so the generic case already
covers them, which is the test of whether it is generic.

A scheduled process gets a timer and a unit that finishes; a long-running one
gets a unit that is restarted when it exits. Getting that wrong either way is a
second copy running continuously between fires, or a schedule that never fires.
The modes are exclusive and validation says so near the author: something that
runs once does not run on a schedule, and something not running between fires
cannot be restarted when a file changes.

A missed fire happens when the machine comes back rather than being skipped,
which is the difference between a machine that was down and a schedule that
quietly stopped.

Claude-Session: https://claude.ai/code/session_01D6qtiYU3P9jk3pnAXyAFyx

internal/declaration/cron_test.go

@@ -11,19 +11,19 @@ import (
 
 func TestParseCronRefusesMalformed(t *testing.T) {
 	for _, expr := range []string{
-		"",                  // nothing
-		"* * * *",           // four fields
-		"* * * * * *",       // six fields
-		"60 * * * *",        // minute out of range
-		"* 24 * * *",        // hour out of range
-		"* * 0 * *",         // day-of-month below 1
-		"* * 32 * *",        // day-of-month above 31
-		"* * * 13 *",        // month out of range
-		"* * * * 8",         // day-of-week above 7
-		"a * * * *",         // not a number
-		"*/0 * * * *",       // zero step
-		"5-1 * * * *",       // inverted range
-		"1,,2 * * * *",      // empty element
+		"",             // nothing
+		"* * * *",      // four fields
+		"* * * * * *",  // six fields
+		"60 * * * *",   // minute out of range
+		"* 24 * * *",   // hour out of range
+		"* * 0 * *",    // day-of-month below 1
+		"* * 32 * *",   // day-of-month above 31
+		"* * * 13 *",   // month out of range
+		"* * * * 8",    // day-of-week above 7
+		"a * * * *",    // not a number
+		"*/0 * * * *",  // zero step
+		"5-1 * * * *",  // inverted range
+		"1,,2 * * * *", // empty element
 	} {
 		if _, err := ParseCron(expr); err == nil {
 			t.Errorf("a malformed cron %q was accepted", expr)
@@ -33,13 +33,13 @@ func TestParseCronRefusesMalformed(t *testing.T) {
 
 func TestParseCronAcceptsTheOrdinaryForms(t *testing.T) {
 	for _, expr := range []string{
-		"* * * * *",         // every minute
-		"0 3 * * *",         // 03:00 daily
-		"*/15 * * * *",      // every 15 minutes
-		"0 0 1 1 *",         // new year
-		"0 9-17 * * 1-5",    // business hours, weekdays
-		"0 0 * * 7",         // Sunday as 7
-		"0,30 * * * *",      // twice an hour
+		"* * * * *",      // every minute
+		"0 3 * * *",      // 03:00 daily
+		"*/15 * * * *",   // every 15 minutes
+		"0 0 1 1 *",      // new year
+		"0 9-17 * * 1-5", // business hours, weekdays
+		"0 0 * * 7",      // Sunday as 7
+		"0,30 * * * *",   // twice an hour
 	} {
 		if _, err := ParseCron(expr); err != nil {
 			t.Errorf("a valid cron %q was refused: %v", expr, err)