feat: switch stealth Chromium default channel to consumer Chrome

Playwright's bundled Chromium has a distinct build fingerprint (build ID,
uniform WebGL/codec lists, HeadlessChrome residue) that anti-bot services
increasingly flag. Driving a system-installed Google Chrome via Playwright's
channel option sheds that signal and aligns sec-ch-ua with UA more cleanly.

Changes:
- Add BrowserOptions.Channel string field (chrome, chrome-beta, chromium,
  msedge; empty = default).
- When stealth+headless+Chromium and Channel is empty, default to "chrome"
  (was "chromium"). Explicit Channel values always win, so callers can opt
  back to "chromium" or pick another channel.
- Merge Channel in mergeOptions.
- Expose --channel/--ch flag on cmd/browser for A/B fingerprint testing.

Callers must have the chosen browser installed on the host
(e.g. `playwright install chrome`). Firefox and WebKit paths are untouched.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

browser_init.go

@@ -104,8 +104,17 @@ func initBrowser(opt BrowserOptions) (*browserInitResult, error) {
 		if len(launchArgs) > 0 {
 			launchOpts.Args = launchArgs
 		}
-		if stealth && opt.Browser == BrowserChromium && headless {
-			launchOpts.Channel = playwright.String("chromium")
+		if opt.Browser == BrowserChromium {
+			channel := opt.Channel
+			if channel == "" && stealth && headless {
+				// Real Chrome sheds Playwright's bundled-Chromium fingerprint
+				// (build ID, uniform WebGL, HeadlessChrome residue) that
+				// anti-bot services increasingly flag.
+				channel = "chrome"
+			}
+			if channel != "" {
+				launchOpts.Channel = playwright.String(channel)
+			}
 		}
 		browser, err = bt.Launch(launchOpts)
 		if err != nil {
@@ -216,6 +225,9 @@ func mergeOptions(base BrowserOptions, opts []BrowserOptions) BrowserOptions {
 		if o.Stealth != nil {
 			base.Stealth = o.Stealth
 		}
+		if o.Channel != "" {
+			base.Channel = o.Channel
+		}
 	}
 	return base
 }

cmd/browser/pkg/browser/flags.go

@@ -46,6 +46,11 @@ var Flags = BrowserFlags{
 		Usage:       "Disable stealth mode (anti-bot-detection evasions are enabled by default)",
 		DefaultText: "false",
 	},
+	&cli.StringFlag{
+		Name:    "channel",
+		Usage:   "Chromium channel to launch (chrome, chrome-beta, chromium, msedge). Only applies when --browser=chromium. Empty = stealth default (chrome).",
+		Aliases: []string{"ch"},
+	},
 }
 
 func FromCommand(ctx context.Context, cmd *cli.Command) (extractor.Browser, error) {
@@ -83,5 +88,9 @@ func FromCommand(ctx context.Context, cmd *cli.Command) (extractor.Browser, erro
 		opts.Stealth = extractor.Bool(false)
 	}
 
+	if ch := cmd.String("channel"); ch != "" {
+		opts.Channel = ch
+	}
+
 	return extractor.NewBrowser(ctx, opts)
 }

playwright.go

@@ -90,6 +90,15 @@ type BrowserOptions struct {
 	// evasions are applied automatically (launch args + init scripts). When nil,
 	// defaults to true in NewBrowser / NewInteractiveBrowser.
 	Stealth *bool
+
+	// Channel selects a Chromium-family browser channel when Browser is
+	// BrowserChromium. Accepted values include "chrome", "chrome-beta",
+	// "chromium", "msedge". Empty defaults to "chrome" when stealth+headless
+	// (real Chrome sheds the bundled-Chromium fingerprint); otherwise falls
+	// back to Playwright's bundled browser. The chosen channel must be
+	// installed on the host (e.g. `playwright install chrome`). Ignored when
+	// Browser is not BrowserChromium.
+	Channel string
 }
 
 func sameSiteToPlaywright(s SameSite) *playwright.SameSiteAttribute {