feat(agent): add crash logs and watchdog startup

- Recover panics to disk for diagnostics
- Add 5-minute watchdog task with startup
- Add -ensure flag to start detached agent
- Add script to pull remote folder via API

lib/crashlog/crashlog.go

@@ -0,0 +1,58 @@
+package crashlog
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime/debug"
+	"sync"
+	"time"
+
+	"tea.chunkbyte.com/kato/go-worm/lib/config"
+)
+
+var mu sync.Mutex
+
+// Recover logs a panic and re-raises after writing the crash file.
+func Recover() {
+	if r := recover(); r != nil {
+		_ = write("panic", fmt.Sprint(r), debug.Stack())
+		panic(r)
+	}
+}
+
+// RecordPanic writes a recovered panic without exiting (e.g. HTTP handlers).
+func RecordPanic(recovered any) {
+	_ = write("panic", fmt.Sprint(recovered), debug.Stack())
+}
+
+// RecordError writes a fatal error before exit.
+func RecordError(err error) {
+	if err == nil {
+		return
+	}
+	_ = write("fatal", err.Error(), debug.Stack())
+}
+
+func write(kind, detail string, stack []byte) error {
+	dir, err := config.LogsDir()
+	if err != nil {
+		return err
+	}
+	mu.Lock()
+	defer mu.Unlock()
+	if err := os.MkdirAll(dir, 0o700); err != nil {
+		return err
+	}
+	name := fmt.Sprintf("crash-%s.log", time.Now().Format("2006-01-02-150405"))
+	path := filepath.Join(dir, name)
+	body := fmt.Sprintf(
+		"time: %s\nversion: %s\nkind: %s\ndetail: %s\n\nstack:\n%s",
+		time.Now().Format(time.RFC3339Nano),
+		config.Version,
+		kind,
+		detail,
+		stack,
+	)
+	return os.WriteFile(path, []byte(body), 0o600)
+}

lib/crashlog/crashlog_test.go

@@ -0,0 +1,38 @@
+package crashlog
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"tea.chunkbyte.com/kato/go-worm/lib/config"
+)
+
+func TestWrite(t *testing.T) {
+	base := t.TempDir()
+	t.Setenv("XDG_CONFIG_HOME", base)
+	t.Setenv("APPDATA", base)
+
+	if err := write("test", "boom", []byte("trace")); err != nil {
+		t.Fatal(err)
+	}
+	dir := filepath.Join(base, config.AppDataDir, config.LogsSubdir)
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(entries) != 1 {
+		t.Fatalf("entries = %d, want 1", len(entries))
+	}
+	data, err := os.ReadFile(filepath.Join(dir, entries[0].Name()))
+	if err != nil {
+		t.Fatal(err)
+	}
+	text := string(data)
+	for _, part := range []string{"kind: test", "detail: boom", "trace", config.Version} {
+		if !strings.Contains(text, part) {
+			t.Fatalf("log missing %q: %s", part, text)
+		}
+	}
+}