Run the merge queue on a state-driven coordinator

internal/agents/coordinator.go

@@ -0,0 +1,57 @@
+package agents
+
+import (
+	"context"
+	"log/slog"
+)
+
+const abandonedMergeText = "The Merge turn ended unfinished (interrupted, failed to start, or with no final message), so byre didn't squash or push the task. Merge again to retry."
+
+func (m *Manager) poke() {
+	select {
+	case m.pokes <- struct{}{}:
+	default:
+	}
+}
+
+func (m *Manager) coordinate() {
+	finalizing := map[string]bool{}
+	for {
+		select {
+		case <-m.watchStop:
+			return
+		case <-m.pokes:
+			m.coordinateMerges(context.Background(), finalizing)
+		}
+	}
+}
+
+func (m *Manager) coordinateMerges(ctx context.Context, finalizing map[string]bool) {
+	work, err := m.store.CoordinateMerges(ctx)
+	if err != nil {
+		slog.Error("coordinate merges", "err", err)
+		return
+	}
+	for _, id := range work.Abandoned {
+		slog.Info("merge turn ended unfinished", "task", id)
+		m.fileError(ctx, id, abandonedMergeText)
+		m.deliverIdle(ctx, id)
+	}
+	for _, c := range work.Start {
+		m.startClaimedMerge(ctx, c)
+	}
+	current := map[string]bool{}
+	for _, f := range work.Finalize {
+		current[f.Task.Id] = true
+		if finalizing[f.Task.Id] {
+			continue
+		}
+		finalizing[f.Task.Id] = true
+		go m.finalizeMerge(f)
+	}
+	for id := range finalizing {
+		if !current[id] {
+			delete(finalizing, id)
+		}
+	}
+}