fix(driver): skip pre-erase for replace-on-input drivers

The web driver's InputText already replaces content via select-all, so
the runner's unconditional EraseText was a redundant round-trip on
every InputText. A new optional TextReplacer capability lets a driver
assert replace semantics; the runner skips the erase when asserted.

internal/driver/chrome/driver.go

@@ -193,6 +193,12 @@ func (d *Driver) InputText(_ context.Context, text string) error {
 	)
 }
 
+// ReplacesTextOnInput reports that InputText replaces existing content via
+// select-all, so the runner skips its pre-erase.
+func (d *Driver) ReplacesTextOnInput() bool {
+	return true
+}
+
 // EraseText clears the focused field. InputText above already replaces via
 // select-all, so the character count is not needed to bound the deletion.
 func (d *Driver) EraseText(_ context.Context, _ int) error {

internal/driver/driver.go

@@ -60,6 +60,16 @@ type ForegroundChecker interface {
 	ForegroundApp(ctx context.Context) (string, error)
 }
 
+// TextReplacer is the optional capability for drivers whose InputText already
+// replaces the field's content instead of appending to it. The runner must
+// skip its pre-erase for such drivers: the erase would be a redundant
+// round-trip on every InputText.
+type TextReplacer interface {
+	// ReplacesTextOnInput reports whether InputText replaces existing
+	// content, making the runner's pre-erase unnecessary.
+	ReplacesTextOnInput() bool
+}
+
 // FocusedWindowChecker is the optional capability for reporting which app owns
 // the focused (on-screen) window. The startup gate prefers it over
 // ForegroundChecker: the resumed-activity signal flips to a freshly launched

internal/driver/mock/mock.go

@@ -63,6 +63,10 @@ type Driver struct {
 	MetricsData   driver.Metrics
 	Failures      map[ActionKind]error
 
+	// ReplacesText makes the mock assert the TextReplacer capability, so
+	// tests cover both the erase-before-type and replace-on-input paths.
+	ReplacesText bool
+
 	// ForegroundResults is consumed one entry per ForegroundApp call (the
 	// last entry repeats). Empty yields "", which disables the runner's
 	// app-scope guard so tests that don't care are unaffected.
@@ -212,6 +216,12 @@ func (d *Driver) InputText(ctx context.Context, text string) error {
 	return nil
 }
 
+func (d *Driver) ReplacesTextOnInput() bool {
+	d.mutex.Lock()
+	defer d.mutex.Unlock()
+	return d.ReplacesText
+}
+
 func (d *Driver) EraseText(ctx context.Context, characterCount int) error {
 	if err := d.failure(ActionEraseText); err != nil {
 		return err