fix(core): use a monotonic clock for the drain watchdog

Addresses review feedback: Date.now() is wall-clock time, so an NTP
adjustment or VM migration could fire the stall watchdog prematurely
(clock jumps forward) or delay it (clock jumps backward).
performance.now() is monotonic and immune to clock adjustments. The
wall-clock Date.now() uses for history timestamps are untouched.

Author: MartinCajiao

packages/core/src/services/shellExecutionService.ts

@@ -1061,10 +1061,11 @@ export class ShellExecutionService {
 
       // Updated every time an output chunk settles so the post-exit drain
       // watchdog only fires when the chain is stuck, never while it is
-      // slow but advancing.
-      let lastDrainActivityAt = Date.now();
+      // slow but advancing. Uses the monotonic clock: wall-clock (Date.now)
+      // adjustments, e.g. NTP, must not fire or delay the watchdog.
+      let lastDrainActivityAt = performance.now();
       const markDrainActivity = () => {
-        lastDrainActivityAt = Date.now();
+        lastDrainActivityAt = performance.now();
       };
 
       let isStreamingRawContent = true;
@@ -1415,7 +1416,10 @@ export class ShellExecutionService {
           markDrainActivity();
           const drainStalled = new Promise<'drain-stalled'>((res) => {
             drainWatchdog = setInterval(() => {
-              if (Date.now() - lastDrainActivityAt >= DRAIN_STALL_TIMEOUT_MS) {
+              if (
+                performance.now() - lastDrainActivityAt >=
+                DRAIN_STALL_TIMEOUT_MS
+              ) {
                 res('drain-stalled');
               }
             }, DRAIN_STALL_POLL_MS);