fix(fetch): make navigator.webdriver value an explicit config choice

Addresses Law 1 concern: the webdriver patch value was hardcoded to
`undefined`, which is an implicit behavior choice that fails Rebrowser
while passing other detectors.

Introduces WebdriverValue enum (False | Undefined) on BrowserFetchConfig:
- False (default): matches real non-automated Chrome behavior
- Undefined: property appears deleted, passes classic detectors

Default changed from `undefined` to `false`. This is now an explicit,
auditable config input — not hidden detection-driven logic.

Live test results after fix:
- Rebrowser: 10/10 PASS (was 9/10, webdriver now passes)
- Sannysoft: 55/56 PASS (PluginArray prototype, unchanged)
- All 5 stealth tests green

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: copyleftdev

crates/palimpsest-fetch/src/browser.rs

@@ -33,6 +33,24 @@ use url::Url;
 
 use crate::result::FetchResult;
 
+/// What value `navigator.webdriver` should report in stealth mode.
+///
+/// Real Chrome returns `false` when not under automation. Some older
+/// detectors flag `false` as suspicious (they expect `true` for
+/// headless). Others flag `undefined` as "manually deleted." This
+/// is an explicit, auditable config choice — not hidden behavior.
+#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
+pub enum WebdriverValue {
+    /// Return `false` — matches real non-automated Chrome.
+    /// Passes Rebrowser, Sannysoft, BotD. May trigger older heuristics
+    /// that specifically check `=== false`.
+    #[default]
+    False,
+    /// Return `undefined` — property appears deleted.
+    /// Passes most classic detectors but Rebrowser flags as "manually deleted."
+    Undefined,
+}
+
 /// Configuration for the browser fetcher.
 #[derive(Debug, Clone)]
 pub struct BrowserFetchConfig {
@@ -46,6 +64,9 @@ pub struct BrowserFetchConfig {
     /// viewport parity, and permissions. All noise is seeded from
     /// CrawlSeed for determinism (Law 1).
     pub stealth: bool,
+    /// What `navigator.webdriver` should return in stealth mode.
+    /// Default: `False` (matches real Chrome behavior).
+    pub webdriver_value: WebdriverValue,
 }
 
 impl Default for BrowserFetchConfig {
@@ -57,6 +78,7 @@ impl Default for BrowserFetchConfig {
             js_enabled: true,
             user_agent: "PalimpsestBot/0.1".into(),
             stealth: false,
+            webdriver_value: WebdriverValue::default(),
         }
     }
 }
@@ -575,6 +597,12 @@ fn build_stealth_script(
     let vh = config.viewport_height;
     let ua = &config.user_agent;
 
+    // Webdriver value from config (Law 1: explicit, auditable choice).
+    let webdriver_js = match config.webdriver_value {
+        WebdriverValue::False => "false",
+        WebdriverValue::Undefined => "undefined",
+    };
+
     // Derive sub-seeds for noise patches (Law 1: deterministic).
     let canvas_seed = seed_value.wrapping_mul(0x9E3779B97F4A7C15).wrapping_add(1);
     let audio_seed = seed_value.wrapping_mul(0x9E3779B97F4A7C15).wrapping_add(2);
@@ -583,9 +611,10 @@ fn build_stealth_script(
     let stealth = format!(
         r#"
         // === STEALTH PATCH 1: navigator.webdriver ===
-        // Set to undefined on the prototype, not false (detectors flag false).
+        // Value is an explicit config choice (WebdriverValue enum), not hidden.
+        // False = real Chrome behavior. Undefined = property deleted.
         Object.defineProperty(Navigator.prototype, 'webdriver', {{
-            get: () => undefined,
+            get: () => {webdriver_js},
             configurable: true
         }});
 

crates/palimpsest-fetch/tests/stealth_test.rs

@@ -127,8 +127,9 @@ fn stealth_script(seed: CrawlSeed) -> String {
         }}
 
         // === STEALTH ===
+        // Value: false matches real non-automated Chrome.
         Object.defineProperty(Navigator.prototype, 'webdriver', {{
-            get: () => undefined,
+            get: () => false,
             configurable: true
         }});