internal/pkg: pending error alongside done channel

This significantly simplifies synchronisation of access to identErr.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/pkg.go

@@ -560,6 +560,8 @@ func newToplevel(ctx context.Context) *toplevel {
 type pendingCure struct {
 	// Closed on cure completion.
 	done <-chan struct{}
+	// Error outcome, safe to access after done is closed.
+	err error
 	// Cancels the corresponding cure.
 	cancel context.CancelFunc
 }
@@ -1065,7 +1067,7 @@ func (c *Cache) loadOrStoreIdent(id unique.Handle[ID]) (
 		<-pending.done
 		c.identMu.RLock()
 		if checksum, ok = c.ident[id]; !ok {
-			err = c.identErr[id]
+			err = pending.err
 		}
 		c.identMu.RUnlock()
 		return
@@ -1091,6 +1093,7 @@ func (c *Cache) finaliseIdent(
 ) {
 	c.identMu.Lock()
 	if err != nil {
+		c.identPending[id].err = err
 		c.identErr[id] = err
 	} else {
 		c.ident[id] = checksum