Re-vendor the shared files from sneak/prompts at dd4027b (closes #52)

Takes .golangci.yml, .dockerignore, .gitignore, .editorconfig, the
workflow and REPO_POLICIES.md from sneak/prompts dd4027b, keeping this
repository's own entries after the shared content. Lint (golangci-lint
v2.14.0) and test become Dockerfile phases that script/lint and
script/test build alone and uncached; the image build depends on both,
and script/cibuild bootstraps, runs script/check, then builds the image.
The agent guidance file moves to AGENTS.md. The Go code is fixed for
what the new configuration finds; reads that iterate rows now also
report an iteration error.

Model: opus-5-5

cmd/streamdumper/main.go

@@ -26,9 +26,17 @@ func main() {
 
 	// Register raw message handler that prints to stdout
 	s.RegisterRawHandler(func(line string) {
-		fmt.Println(line)
+		_, _ = fmt.Fprintln(os.Stdout, line)
 	})
 
+	// Start streaming before any defer: log.Fatal exits without running
+	// deferred calls.
+	err := s.Start(context.Background())
+	if err != nil {
+		log.Fatal("Failed to start streamer:", err)
+	}
+	defer s.Stop()
+
 	// Set up context with cancellation
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
@@ -36,18 +44,13 @@ func main() {
 	// Handle signals
 	sigChan := make(chan os.Signal, 1)
 	signal.Notify(sigChan, os.Interrupt, syscall.SIGTERM)
+
 	go func() {
 		<-sigChan
 		log.Println("Received shutdown signal")
 		cancel()
 	}()
 
-	// Start streaming
-	if err := s.Start(); err != nil {
-		log.Fatal("Failed to start streamer:", err)
-	}
-	defer s.Stop()
-
 	// Wait for context cancellation
 	<-ctx.Done()
 }