Commit history detached from cancellation on every path, not just failure (#73)

Co-authored-by: Steve Dudenhoeffer <[email protected]>

internal/service/revisions.go

@@ -130,11 +130,7 @@ func (s *Service) WithChangeSet(ctx context.Context, actorID, gardenID int64, op
 		// which is exactly the situation undo exists for. Record what happened,
 		// mark the summary, and still report the failure.
 		sc.summary = partialSummary(sc.summary)
-		// Detached from cancellation on purpose. The commonest reason fn failed is
-		// that ctx was cancelled or timed out — and using that same dead context
-		// to record what committed would fail too, losing the history for changes
-		// that really happened. That is precisely the case this path exists for.
-		if _, cerr := s.commitScope(context.WithoutCancel(ctx), sc, nil); cerr != nil {
+		if _, cerr := s.commitScope(ctx, sc, nil); cerr != nil {
 			slog.Error("service: partial turn could not be recorded", "error", cerr, "garden", gardenID)
 		}
 		return nil, err
@@ -154,11 +150,19 @@ func partialSummary(summary string) string {
 // commitScope writes a scope's buffered revisions as one change set. revertsID is
 // set only by RevertChangeSet. A scope with no revisions writes nothing — an
 // operation that changed nothing doesn't belong in history.
+//
+// The write is DETACHED FROM CANCELLATION, always, and that belongs here rather
+// than at each call site so no caller can be the one that forgets. By the time a
+// commit runs, the data changes it describes have already been written — so
+// cancelling it cannot undo anything. It can only lose the record of what
+// happened and leave real changes with no way to undo them, which is the one
+// thing the whole change-set design exists to prevent.
 func (s *Service) commitScope(ctx context.Context, sc *changeScope, revertsID *int64) (*domain.ChangeSet, error) {
 	revs := sc.taken()
 	if len(revs) == 0 {
 		return nil, nil
 	}
+	ctx = context.WithoutCancel(ctx)
 	return s.store.WriteChangeSet(ctx, &domain.ChangeSet{
 		GardenID:   sc.gardenID,
 		ActorID:    sc.actorID,
@@ -199,9 +203,13 @@ func (s *Service) record(ctx context.Context, gardenID, actorID int64, summary s
 		sc.append(revs)
 		return
 	}
-	if _, err := s.store.WriteChangeSet(ctx, &domain.ChangeSet{
-		GardenID: gardenID, ActorID: actorID, Source: domain.SourceUI, Summary: summary,
-	}, revs); err != nil {
+	// Auto-scope: one operation, its own change set. Written through the same
+	// detached path as everything else — a REST client that hangs up right after
+	// its PATCH landed must not leave that change without history, and this is
+	// the path virtually every mutation takes.
+	auto := &changeScope{gardenID: gardenID, actorID: actorID, source: domain.SourceUI, summary: summary}
+	auto.append(revs)
+	if _, err := s.commitScope(ctx, auto, nil); err != nil {
 		slog.Error("service: record change set", "error", err, "garden", gardenID, "summary", summary)
 	}
 }
@@ -312,10 +320,9 @@ func (s *Service) RevertChangeSet(ctx context.Context, actorID, changeSetID int6
 		changes, conflict, err := s.applyInverse(ctx, r, applied)
 		if err != nil {
 			// Record what actually landed before surfacing the failure, so the
-			// partial revert is visible and undoable rather than orphaned. Detached
-			// from cancellation for the same reason as WithChangeSet's path: a
-			// timed-out context can't be used to write the record of what it did.
-			if _, cerr := s.commitScope(context.WithoutCancel(ctx), sc, &target.ID); cerr != nil {
+			// partial revert is visible and undoable rather than orphaned.
+			// (commitScope detaches from cancellation itself.)
+			if _, cerr := s.commitScope(ctx, sc, &target.ID); cerr != nil {
 				slog.Error("service: partial revert could not be recorded", "error", cerr, "changeSet", changeSetID)
 			}
 			return nil, nil, err