refactor(runner): collapse WebDriver forks behind ActionSource/ExtractorSource

internal/runner/source.go

@@ -0,0 +1,72 @@
+package runner
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"github.com/priyanshujain/sanderling/internal/driver"
+	"github.com/priyanshujain/sanderling/internal/verifier"
+)
+
+// ActionSource resolves the next action for a step. Both runtimes (the goja
+// picker and the web/V8 picker) implement it so the runner loop has one path
+// and no per-step driver type assertion. NextAction returns verifier.ErrNoAction
+// when the picker declined to act this tick.
+type ActionSource interface {
+	NextAction(ctx context.Context) (verifier.Action, error)
+}
+
+// ExtractorSource yields per-step extractor overrides the runner applies after
+// PushSnapshot. The mobile path has none (returns nil); the web path returns the
+// values its extractors computed in V8 against the real DOM.
+type ExtractorSource interface {
+	ExtractorOverrides(ctx context.Context) (map[int]json.RawMessage, error)
+}
+
+// gojaSource drives both action selection and (trivially) extractor overrides
+// for the mobile path, where the goja-bundled picker runs in-process and no V8
+// extractor values exist.
+type gojaSource struct {
+	verifier *verifier.Verifier
+}
+
+func (s gojaSource) NextAction(context.Context) (verifier.Action, error) {
+	return s.verifier.NextAction()
+}
+
+func (gojaSource) ExtractorOverrides(context.Context) (map[int]json.RawMessage, error) {
+	return nil, nil
+}
+
+// webSource adapts the chrome driver's V8 picker: it evaluates the bundled
+// __sanderlingNextAction__ / __sanderlingExtractors__ globals and decodes their
+// JSON into the unified action and override shapes.
+type webSource struct {
+	web driver.WebDriver
+}
+
+func (s webSource) NextAction(ctx context.Context) (verifier.Action, error) {
+	raw, err := s.web.NextActionFromV8(ctx)
+	if err != nil {
+		return verifier.Action{}, fmt.Errorf("v8 next action: %w", err)
+	}
+	// Both engines emit the unified flat camelCase wire contract; one decoder
+	// reads it. A null payload means the generator declined to act this tick.
+	return verifier.DecodeAction(raw)
+}
+
+func (s webSource) ExtractorOverrides(ctx context.Context) (map[int]json.RawMessage, error) {
+	return s.web.EvaluateExtractors(ctx)
+}
+
+// pickSources selects the runtime's action and extractor sources ONCE at setup
+// from the driver's capabilities, so the step loop never type-asserts.
+func pickSources(options Options) (ActionSource, ExtractorSource) {
+	if web, ok := options.Driver.(driver.WebDriver); ok {
+		source := webSource{web: web}
+		return source, source
+	}
+	source := gojaSource{verifier: options.Verifier}
+	return source, source
+}