feat(runner): bound every device call and record the actions that never reached the app

observation and apply now run under a timeout, so a driver that stops answering ends the step rather than the run. an undelivered gesture and a selector that matched nothing are recorded as their own skip reasons instead of counting toward the apply-failure streak, a failed observation is counted apart from a screen with nothing on it, and the summary names both. resolveCoordinates hands a point outside the viewport to the driver rather than dropping it: only the driver knows whether it can scroll that point back into reach. exceptions and navigations are collected per step and a Scroll goes to a driver's Scroller when it has one.

internal/runner/navigation_trace_test.go

@@ -0,0 +1,82 @@
+package runner
+
+import (
+	"bufio"
+	"context"
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/priyanshujain/sanderling/internal/driver"
+	mockdriver "github.com/priyanshujain/sanderling/internal/driver/mock"
+	"github.com/priyanshujain/sanderling/internal/trace"
+)
+
+// navigatingDriver reports one navigation per step, the way a page that submits
+// a form or reloads does.
+type navigatingDriver struct {
+	*mockdriver.Driver
+	url string
+}
+
+func (d *navigatingDriver) Navigations(context.Context) ([]driver.Navigation, error) {
+	return []driver.Navigation{{URL: d.url, UnixMillis: 1700000000000}}, nil
+}
+
+// A run whose app replaced its own document has to say so on the step it
+// happened. Without it the trace shows a generator repeating one action and no
+// reason for it, and an analysis cannot tell that from a seed that chose badly.
+func TestRunner_TheTraceRecordsThatThePageNavigated(t *testing.T) {
+	state := newHarness(t)
+	const url = "http://127.0.0.1/index.html?"
+	navigating := &navigatingDriver{Driver: state.mock, url: url}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	if _, err := Run(ctx, Options{
+		Duration:    100 * time.Millisecond,
+		IdleTimeout: 20 * time.Millisecond,
+		MaxSteps:    3,
+		Driver:      navigating,
+		Verifier:    state.verifier,
+		TraceWriter: state.writer,
+	}); err != nil {
+		t.Fatalf("Run: %v", err)
+	}
+	if err := state.writer.Close(); err != nil {
+		t.Fatalf("close trace: %v", err)
+	}
+
+	file, err := os.Open(filepath.Join(state.writer.Directory(), "trace.jsonl"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file.Close()
+
+	recorded := 0
+	scanner := bufio.NewScanner(file)
+	scanner.Buffer(make([]byte, 0, 64*1024), 8*1024*1024)
+	for scanner.Scan() {
+		var step struct {
+			Index       int                `json:"step"`
+			Navigations []trace.Navigation `json:"navigations"`
+		}
+		if err := json.Unmarshal(scanner.Bytes(), &step); err != nil {
+			t.Fatalf("trace line decode: %v", err)
+		}
+		for _, navigation := range step.Navigations {
+			recorded++
+			if navigation.URL != url {
+				t.Errorf("step %d records navigation to %q, want %q", step.Index, navigation.URL, url)
+			}
+			if navigation.UnixMillis == 0 {
+				t.Errorf("step %d records a navigation with no timestamp", step.Index)
+			}
+		}
+	}
+	if recorded == 0 {
+		t.Fatal("the page navigated on every step and the trace holds no record of it")
+	}
+}