Move Go service orchestration to contrib/claude

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

contrib/claude/go-service.md

@@ -0,0 +1,53 @@
+# Go Service Orchestration
+
+A top-level `Run` method starts child subsystems (workers, servers) as goroutines via `sync.WaitGroup.Go`. Each child gets its own cancellable context created with `context.WithCancel(context.WithoutCancel(ctx))` so that a parent cancellation does not kill in-flight work — the parent explicitly calls each `stop*` function and then `wg.Wait()` for a controlled shutdown.
+
+When a child crashes, it calls `cancel(fmt.Errorf("… crashed: %w", err))` to signal the parent.
+
+```go
+func (impl *Implm) Run(ctx context.Context, l *log.Logger) error {
+	wg := sync.WaitGroup{}
+	ctx, cancel := context.WithCancelCause(ctx)
+	defer cancel(context.Canceled)
+
+	// Start a worker
+	workerCtx, stopWorker := context.WithCancel(context.WithoutCancel(ctx))
+	worker := NewFooWorker(pgClient, l.Named("foo-worker"))
+	wg.Go(
+		func() {
+			if err := worker.Run(workerCtx); err != nil {
+				cancel(fmt.Errorf("foo worker crashed: %w", err))
+			}
+		},
+	)
+
+	// Start a server
+	serverCtx, stopServer := context.WithCancel(context.WithoutCancel(ctx))
+	defer stopServer()
+	wg.Go(
+		func() {
+			if err := impl.runServer(serverCtx, l); err != nil {
+				cancel(fmt.Errorf("server crashed: %w", err))
+			}
+		},
+	)
+
+	<-ctx.Done()
+
+	stopServer()
+	stopWorker()
+
+	wg.Wait()
+
+	return context.Cause(ctx)
+}
+```
+
+## Key principles
+
+- **`context.WithCancelCause`** — the parent uses this to track why it's shutting down
+- **`context.WithoutCancel`** — each child gets an independent context so parent cancellation doesn't kill in-flight work
+- **`context.WithCancel` on the detached context** — gives the parent an explicit `stop*` function for each child
+- **Crash propagation** — when a child fails, it calls `cancel(fmt.Errorf("… crashed: %w", err))` to signal the parent
+- **Ordered shutdown** — `<-ctx.Done()` triggers, then each `stop*` is called, then `wg.Wait()` blocks until all children finish
+- **`context.Cause(ctx)`** — returns the original error that caused shutdown