Rotate a database target's archive monthly, daily or hourly (closes #379)

A database target's rotation setting (none, monthly, daily or hourly) puts the UTC period of each event's receive time in its archive file name, so each file holds exactly its period's events. It is on the new webhook page and both target forms, and shown in the target list. Renames move every one of a target's files and move them all back if one fails. The sweep prunes one file at a time under the target's lock and deletes a rotated file it leaves empty. Download opens one file at a time, oldest period first, finding each again under the target's current name. The target list names the current file and totals all of them.

Model: opus-5-5

internal/delivery/export_test.go

@@ -501,23 +501,32 @@ func NewExportArchiveWriter(
 	return &ExportArchiveWriter{w: w}
 }
 
-// Write archives a row through the writer.
+// Write archives a row through the writer, into the file named
+// without a period.
 func (e *ExportArchiveWriter) Write(
 	row ExportArchivedEvent, expiry time.Duration,
 ) error {
-	return e.w.write(row, expiry)
+	return e.w.write(row, expiry, "")
+}
+
+// WritePeriod archives a row through the writer, into the file for
+// period.
+func (e *ExportArchiveWriter) WritePeriod(
+	row ExportArchivedEvent, expiry time.Duration, period string,
+) error {
+	return e.w.write(row, expiry, period)
 }
 
 // Open opens the archive file, pruning when expiry is positive.
 func (e *ExportArchiveWriter) Open(expiry time.Duration) error {
-	return e.w.open(expiry)
+	return e.w.open(e.w.path, expiry)
 }
 
 // Reopen closes and reopens the archive file.
 func (e *ExportArchiveWriter) Reopen(
 	expiry time.Duration,
 ) error {
-	return e.w.reopen(expiry)
+	return e.w.reopen(e.w.path, expiry)
 }
 
 // SetNow replaces the clock the writer measures its reopen
@@ -547,7 +556,7 @@ func (e *ExportArchiveWriter) Path() string {
 func (e *ExportArchiveWriter) OpenExisting(
 	expiry time.Duration,
 ) error {
-	return e.w.openMode(archiveModeExisting, expiry)
+	return e.w.openMode(e.w.path, archiveModeExisting, expiry)
 }
 
 // SweepExpired runs an idle sweep of the archive.