Name each database target's archive for its webhook and target (closes #376)

Each database target now has its own archive file,
archive-WEBHOOKNAME-TARGETNAME-TARGETID.db, instead of one
archive-WEBHOOKID.db per webhook. delivery.ArchiveFileName builds the
name: each name is lowercased, keeps ASCII letters and digits, turns
every other run of characters into one dash, and is cut to 40
characters.

Renaming a webhook or a target renames its archive files under the
archive writer's lock, before the new name is saved, and back again if
the save fails. Deleting a target evicts only that target's writer.
Archive files are never deleted, and nothing looks for files under the
old name.

Model: opus-5-5

internal/delivery/archive_sweeper.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"go.uber.org/fx"
+	"gorm.io/gorm"
 	"sneak.berlin/go/webhooker/internal/config"
 	"sneak.berlin/go/webhooker/internal/database"
 	"sneak.berlin/go/webhooker/internal/lifecycle"
@@ -25,14 +26,14 @@ type ArchiveSweeperParams struct {
 	Logger   *logger.Logger
 }
 
-// ArchiveSweeper periodically prunes expired rows from
-// per-webhook archive databases whose database target carries a
-// positive expiry.
+// ArchiveSweeper periodically prunes expired rows from the
+// archive databases of database targets that carry a positive
+// expiry.
 //
 // Without it, pruning happens only when an archive is
 // (re)opened, and archives are only ever reopened by writes: an
-// archive belonging to a webhook that has stopped receiving
-// events would keep its expired rows forever. The sweep closes
+// archive whose target has stopped receiving events would keep
+// its expired rows forever. The sweep closes
 // that gap without changing anything for archives whose expiry
 // is unset or "never".
 //
@@ -155,7 +156,7 @@ func (s *ArchiveSweeper) run(ctx context.Context) {
 // soft-deleted along with it, so GORM's default scope already
 // excludes them.
 //
-// A failure for one webhook is logged and the sweep continues,
+// A failure for one target is logged and the sweep continues,
 // matching how the write path already treats a prune error as
 // non-fatal.
 func (s *ArchiveSweeper) sweep(ctx context.Context) {
@@ -210,19 +211,20 @@ func (s *ArchiveSweeper) sweepTarget(target *database.Target) {
 		return
 	}
 
-	err = s.eng.dbTarget.sweepWebhook(target.WebhookID, expiry)
+	err = s.eng.dbTarget.sweepArchive(target.ID, expiry)
 	if err == nil {
 		return
 	}
 
-	// A writer evicted underneath the sweep means the operator
-	// deleted the webhook (or its last database target) while the
-	// sweep was walking the target list. That is an ordinary
+	// A writer evicted, or a target row gone, underneath the sweep
+	// means the operator deleted the target or its webhook while
+	// the sweep was walking the target list. That is an ordinary
 	// interleaving, not a failure, so it must not produce an
 	// error line.
-	if errors.Is(err, errArchiveWriterEvicted) {
+	if errors.Is(err, errArchiveWriterEvicted) ||
+		errors.Is(err, gorm.ErrRecordNotFound) {
 		s.log.Debug(
-			"archive sweep: writer evicted mid-sweep",
+			"archive sweep: target deleted mid-sweep",
 			"webhook_id", target.WebhookID,
 			"target_id", target.ID,
 		)