feat: Add event-based automation triggers (#2537)

src/health.ts

@@ -0,0 +1,16 @@
+// Returned by `addListener`; invoke it to stop listening.
+export type UnlistenCallback = () => void;
+
+// A source of health information: the current failures (of some domain-specific
+// shape `F`) and a way to observe changes to them.
+interface HealthInterface<F> {
+  getFailures(): F[];
+  addListener(listener: () => void): UnlistenCallback;
+}
+
+// Health that also supports a user-driven retry of whatever is currently
+// failing. Separate from HealthInterface because observation and recovery are
+// distinct capabilities: a read-only health source has nothing to retry.
+export interface RecoverableHealthInterface<F> extends HealthInterface<F> {
+  retry(): void;
+}