harden proc isolation and filter cross-fork check suite PRs

shell sandbox: double-umount + remount /proc to prevent exfiltration
when agent peels off --mount-proc overlay.

webhooks: filter check_suite.pull_requests to same-repo PRs only
(excludes cross-fork sync PRs) and skip merged/closed PRs.

Co-authored-by: Cursor <cursoragent@cursor.com>

entry

@@ -143955,13 +143955,14 @@ function detectSandboxMethod() {
   log.info("PID namespace isolation not available - falling back to env filtering only");
   return "none";
 }
+var PROC_CLEANUP = "umount /proc 2>/dev/null; umount /proc 2>/dev/null; mount -t proc proc /proc 2>/dev/null;";
 function spawnShell(params) {
   const spawnOpts = { env: params.env, cwd: params.cwd, stdio: params.stdio, detached: true };
   const sandboxMethod = detectSandboxMethod();
   if (sandboxMethod === "unshare") {
     return spawn2(
       "unshare",
-      ["--pid", "--fork", "--mount-proc", "bash", "-c", params.command],
+      ["--pid", "--fork", "--mount-proc", "bash", "-c", `${PROC_CLEANUP} ${params.command}`],
       spawnOpts
     );
   }
@@ -143983,10 +143984,9 @@ function spawnShell(params) {
         "--mount-proc",
         "bash",
         "-c",
-        params.command
+        `${PROC_CLEANUP} ${params.command}`
       ],
       { ...spawnOpts, env: {} }
-      // empty env since we pass via sudo env
     );
   }
   return spawn2("bash", ["-c", params.command], spawnOpts);