feat: watch blueprint.yaml for update and auto resend

Add a file watcher that re-pushes the blueprint to the server whenever
the blueprint file is modified while Newt is running, matching the
reactive behavior of the Docker event monitor.


Former-commit-id: 025497138d

common_test.go

@@ -0,0 +1,146 @@
+package main
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+func TestWatchBlueprintFile_WriteTriggersSend(t *testing.T) {
+	f, err := os.CreateTemp(t.TempDir(), "blueprint-*.yaml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	var calls atomic.Int32
+	go watchBlueprintFile(ctx, f.Name(), func() error {
+		calls.Add(1)
+		return nil
+	})
+
+	time.Sleep(50 * time.Millisecond)
+
+	if err := os.WriteFile(f.Name(), []byte("content"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	time.Sleep(700 * time.Millisecond)
+
+	if calls.Load() != 1 {
+		t.Errorf("expected 1 send call, got %d", calls.Load())
+	}
+}
+
+func TestWatchBlueprintFile_DebounceCoalescesEvents(t *testing.T) {
+	f, err := os.CreateTemp(t.TempDir(), "blueprint-*.yaml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	var calls atomic.Int32
+	go watchBlueprintFile(ctx, f.Name(), func() error {
+		calls.Add(1)
+		return nil
+	})
+
+	time.Sleep(50 * time.Millisecond)
+
+	for i := 0; i < 5; i++ {
+		if err := os.WriteFile(f.Name(), []byte("change"), 0644); err != nil {
+			t.Fatal(err)
+		}
+		time.Sleep(50 * time.Millisecond)
+	}
+
+	time.Sleep(700 * time.Millisecond)
+
+	if calls.Load() != 1 {
+		t.Errorf("expected 1 send call after debounce, got %d", calls.Load())
+	}
+}
+
+func TestWatchBlueprintFile_ContextCancellationStops(t *testing.T) {
+	f, err := os.CreateTemp(t.TempDir(), "blueprint-*.yaml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+
+	done := make(chan struct{})
+	go func() {
+		watchBlueprintFile(ctx, f.Name(), func() error { return nil })
+		close(done)
+	}()
+
+	time.Sleep(50 * time.Millisecond)
+	cancel()
+
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Error("watchBlueprintFile did not exit after context cancellation")
+	}
+}
+
+func TestWatchBlueprintFile_AtomicWriteTriggersSend(t *testing.T) {
+	dir := t.TempDir()
+	target := filepath.Join(dir, "blueprint.yaml")
+	if err := os.WriteFile(target, []byte("initial"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	var calls atomic.Int32
+	go watchBlueprintFile(ctx, target, func() error {
+		calls.Add(1)
+		return nil
+	})
+
+	time.Sleep(50 * time.Millisecond)
+
+	tmp := filepath.Join(dir, "blueprint.yaml.tmp")
+	if err := os.WriteFile(tmp, []byte("updated"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Rename(tmp, target); err != nil {
+		t.Fatal(err)
+	}
+
+	time.Sleep(700 * time.Millisecond)
+
+	if calls.Load() < 1 {
+		t.Errorf("expected at least 1 send call after atomic write, got %d", calls.Load())
+	}
+}
+
+func TestWatchBlueprintFile_MissingFileReturnsGracefully(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	done := make(chan struct{})
+	go func() {
+		watchBlueprintFile(ctx, "/nonexistent/path/blueprint.yaml", func() error { return nil })
+		close(done)
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Error("watchBlueprintFile did not return for missing file")
+	}
+}