sync: update from private repo (11e2d76)

src/engine/browser-session.ts

@@ -108,14 +108,30 @@ export class SessionManager extends EventEmitter {
   }
 
   static isAvailable(): boolean {
-    try {
-      execSync('which Xvfb', { stdio: 'ignore' });
-      execSync('which x11vnc', { stdio: 'ignore' });
-      execSync('which websockify', { stdio: 'ignore' });
-      return true;
-    } catch {
+    // Use the POSIX shell builtin `command -v`, NOT the external `which` binary.
+    // `which` is absent in some minimal images (e.g. debian-slim dropped it from
+    // debianutils) and depends on PATH; relying on it caused "deps missing →
+    // headless fallback" even when Xvfb/x11vnc/websockify were actually installed.
+    // `command -v` is built into /bin/sh, so execSync (which runs via `/bin/sh -c`)
+    // resolves each binary from the server process's own PATH.
+    const required = ['Xvfb', 'x11vnc', 'websockify'];
+    const missing: string[] = [];
+    for (const bin of required) {
+      try {
+        execSync(`command -v ${bin}`, { stdio: 'ignore' });
+      } catch {
+        missing.push(bin);
+      }
+    }
+    if (missing.length > 0) {
+      logger.warn(
+        `[SessionManager] noVNC display stack unavailable; not found on the server PATH: ${missing.join(', ')}. ` +
+        `Browser/CAPTCHA live view (display_mode: novnc) falls back to headless. ` +
+        `Install them (scripts/setup-novnc.sh) and ensure they are on the server process's PATH.`,
+      );
       return false;
     }
+    return true;
   }
 
   private cleanupOrphanedProcesses(): void {