fix(mantis): fence lost Telegram leases without a ten-second delay (#128122)

* perf(mantis): fence lost Telegram leases without delay

* test(mantis): enforce prompt lost-lease fencing

scripts/mantis/run-with-lease-fence.sh

@@ -10,7 +10,7 @@ lost_marker_path="$1"
 shift 2
 
 # The marker records broker-confirmed loss of the shared-account lease; continuing
-# Telegram I/O would violate broker serialization. The <=10s poll window is accepted
+# Telegram I/O would violate broker serialization. The <=1s poll window is accepted
 # against the 20-minute lease TTL.
 # <&0: a backgrounded command's stdin defaults to /dev/null, which silently
 # swallowed the piped agent prompt. The explicit redirect keeps the caller's stdin.
@@ -48,10 +48,5 @@ while true; do
     exit 97
   fi
 
-  for _ in {1..10}; do
-    sleep 1
-    if ! kill -0 "$command_pid" 2>/dev/null; then
-      command_exit
-    fi
-  done
+  sleep 1
 done

test/scripts/run-with-lease-fence.test.ts

@@ -43,13 +43,13 @@ describe("run-with-lease-fence", () => {
       fs.writeFileSync(lostMarker, "lost\n");
 
       try {
-        await expect(waitForChildClose(child, 12_000)).resolves.toEqual({
+        await expect(waitForChildClose(child)).resolves.toEqual({
           code: 97,
           signal: null,
         });
-        const ticksAfterFence = fs.readFileSync(ticksFile, "utf8");
-        await new Promise((resolve) => setTimeout(resolve, 1_200));
-        expect(fs.readFileSync(ticksFile, "utf8")).toBe(ticksAfterFence);
+        expect(() => process.kill(-commandPid, 0)).toThrow(
+          expect.objectContaining({ code: "ESRCH" }),
+        );
         expect(stderr).toContain("::error::Telegram QA lease lost mid-run; fencing proof");
       } finally {
         if (child.exitCode === null) {