fix(browser): robust fetch with incomplete-cache cleanup + retry + binary verification

Root cause: camoufox-js@0.11.0 fetch can exit 0 but silently fail
to download the browser binary when:
1. A partial/incomplete cache from a previous run exists
2. GitHub API rate-limits the unauthenticated release query
3. Network drops mid-download

Fix:
1. run_fetch() now DELETE incomplete cache (dir exists but no
   version.json) before fetching — prevents 'already cached' no-op
2. After fetch, VERIFY version.json exists — if missing, RETRY once
3. After retry, verify Camoufox.app/Contents/MacOS/camoufox exists
4. Log stdout and stderr in INFO traces for debugging

crates/gyandoot-agent/src/browser_manager.rs

@@ -243,15 +243,30 @@ pub async fn init_browser(node_path: Option<&str>) -> BrowserInitResult {
 
 /// Fetch the browser binary using pinned camoufox-js.
 async fn run_fetch(npx: &str, js_version: &str) -> Result<String, String> {
+    let cache = browser_cache_dir();
+
+    // If cache dir exists but is incomplete, nuke it first
+    // (partial downloads from prior aborted runs can confuse camoufox-js)
+    if cache.exists() && !cache.join("version.json").exists() {
+        info!("Removing incomplete cache at {}", cache.display());
+        let _ = std::fs::remove_dir_all(&cache);
+        info!("Will re-download fresh");
+    }
+
     let output = Command::new(npx)
-        .args(&["--yes", &format!("camoufox-js@{}", js_version), "fetch"])
+        .args(&["--yes", &format!("camoufox-js@{js_version}"), "fetch"])
         .output()
         .await
-        .map_err(|e| format!("'{} camoufox-js' not found: {}", npx, e))?;
+        .map_err(|e| format!("'{npx} camoufox-js' not found: {e}"))?;
 
     let stdout = String::from_utf8_lossy(&output.stdout).trim().to_string();
     let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
 
+    info!("camoufox-js fetch stdout: {}", stdout.lines().last().unwrap_or("(empty)"));
+    if !stderr.is_empty() {
+        info!("camoufox-js fetch stderr: {}", stderr.lines().last().unwrap_or("(empty)"));
+    }
+
     if !output.status.success() {
         let detail = if !stderr.is_empty() {
             stderr.lines().filter(|l| l.contains("Error") || l.contains("error")).last().unwrap_or("(check output)")
@@ -261,7 +276,51 @@ async fn run_fetch(npx: &str, js_version: &str) -> Result<String, String> {
         return Err(format!("exit {}: {}", output.status.code().unwrap_or(-1), detail));
     }
 
-    Ok(stdout.lines().filter(|l| l.contains("complete") || l.contains("Installed") || l.contains("Downloaded"))
+    // Verify the download actually produced version.json
+    if !cache.join("version.json").exists() {
+        warn!("camoufox-js exited 0 but version.json not found at {}", cache.display());
+        warn!("This usually means the GitHub release download failed. Retrying once...");
+
+        // Retry once with full output visible
+        let retry_output = Command::new(npx)
+            .args(&["--yes", &format!("camoufox-js@{js_version}"), "fetch"])
+            .output()
+            .await
+            .map_err(|e| format!("Retry failed: {e}"))?;
+
+        let retry_stdout = String::from_utf8_lossy(&retry_output.stdout).trim().to_string();
+        let retry_stderr = String::from_utf8_lossy(&retry_output.stderr).trim().to_string();
+
+        info!("Retry stdout: {}", retry_stdout.lines().last().unwrap_or("(empty)"));
+        if !retry_stderr.is_empty() {
+            info!("Retry stderr: {}", retry_stderr.lines().last().unwrap_or("(empty)"));
+        }
+
+        if !retry_output.status.success() || !cache.join("version.json").exists() {
+            return Err(format!(
+                "Download failed after retry.\n  stdout: {}\n  stderr: {}\n  cache: {}\n\nThis is likely a network/GitHub rate-limit issue.\nTry manually:\n  export GITHUB_TOKEN=your_token\n  {} --yes camoufox-js@{js_version} fetch",
+                retry_stdout.lines().last().unwrap_or("(empty)"),
+                retry_stderr.lines().last().unwrap_or("(empty)"),
+                cache.display(),
+                npx,
+            ));
+        }
+    }
+
+    // Verify the binary exists too
+    let binary_ok = if cfg!(target_os = "macos") {
+        cache.join("Camoufox.app").join("Contents").join("MacOS").join("camoufox").exists()
+    } else {
+        cache.join("camoufox").exists()
+    };
+
+    if !binary_ok {
+        warn!("version.json exists but browser binary missing — possibly corrupted download");
+    }
+
+    Ok(stdout.lines()
+        .chain(stderr.lines())
+        .filter(|l| l.contains("complete") || l.contains("Installed") || l.contains("Downloaded") || l.contains("Camoufox"))
         .last()
         .unwrap_or("Fetch completed")
         .to_string())