feat(web): add automatic actions for open pull requests

A new pr_open alert carries the head commit SHA of each open, non-draft, same-repository pull request. An action with auto enabled sends its webhook once for each pull request and head commit. An authors list limits which pull requests trigger it. The alert never changes repository health.

internal/collector/collector.go

@@ -65,6 +65,7 @@ type Collector struct {
 	log         *slog.Logger
 	webBase     string
 	kick        chan struct{}
+	onRefresh   []func(context.Context, View)
 	names       []string
 	th          config.Thresholds
 	interval    time.Duration
@@ -100,19 +101,33 @@ func New(f Fetcher, cfg *config.Config, log *slog.Logger) *Collector {
 func (c *Collector) Run(ctx context.Context) {
 	t := time.NewTicker(c.interval)
 	defer t.Stop()
-	c.Refresh(ctx)
+	c.refreshAndNotify(ctx)
 	for {
 		select {
 		case <-ctx.Done():
 			return
 		case <-t.C:
-			c.Refresh(ctx)
+			c.refreshAndNotify(ctx)
 		case <-c.kick:
-			c.Refresh(ctx)
+			c.refreshAndNotify(ctx)
 		}
 	}
 }
 
+// OnRefresh registers fn to run after every scan started by Run; call it before Run.
+func (c *Collector) OnRefresh(fn func(context.Context, View)) { c.onRefresh = append(c.onRefresh, fn) }
+
+func (c *Collector) refreshAndNotify(ctx context.Context) {
+	c.Refresh(ctx)
+	if len(c.onRefresh) == 0 || ctx.Err() != nil {
+		return
+	}
+	v := c.View()
+	for _, fn := range c.onRefresh {
+		fn(ctx, v)
+	}
+}
+
 // RequestRefresh asks Run for an extra refresh; it reports false when one is already running or queued.
 func (c *Collector) RequestRefresh() bool {
 	if c.refreshing.Load() {