diff --git a/src/gateway/config-reload.test.ts b/src/gateway/config-reload.test.ts
index 25137aef0..8eee9df30 100644
--- a/src/gateway/config-reload.test.ts
+++ b/src/gateway/config-reload.test.ts
@@ -159,6 +159,12 @@ describe("buildGatewayReloadPlan", () => {
     expect(plan.noopPaths).toContain("secrets.providers.default.path");
   });
 
+  it("treats diagnostics.stuckSessionWarnMs as no-op for gateway restart planning", () => {
+    const plan = buildGatewayReloadPlan(["diagnostics.stuckSessionWarnMs"]);
+    expect(plan.restartGateway).toBe(false);
+    expect(plan.noopPaths).toContain("diagnostics.stuckSessionWarnMs");
+  });
+
   it("defaults unknown paths to restart", () => {
     const plan = buildGatewayReloadPlan(["unknownField"]);
     expect(plan.restartGateway).toBe(true);
diff --git a/src/gateway/config-reload.ts b/src/gateway/config-reload.ts
index 3dedff84c..a1a89717a 100644
--- a/src/gateway/config-reload.ts
+++ b/src/gateway/config-reload.ts
@@ -50,6 +50,8 @@ const MISSING_CONFIG_MAX_RETRIES = 2;
 const BASE_RELOAD_RULES: ReloadRule[] = [
   { prefix: "gateway.remote", kind: "none" },
   { prefix: "gateway.reload", kind: "none" },
+  // Stuck-session warning threshold is read by the diagnostics heartbeat loop.
+  { prefix: "diagnostics.stuckSessionWarnMs", kind: "none" },
   { prefix: "hooks.gmail", kind: "hot", actions: ["restart-gmail-watcher"] },
   { prefix: "hooks", kind: "hot", actions: ["reload-hooks"] },
   {
diff --git a/src/gateway/server.impl.ts b/src/gateway/server.impl.ts
index e2bc0d0bc..414d4db75 100644
--- a/src/gateway/server.impl.ts
+++ b/src/gateway/server.impl.ts
@@ -372,7 +372,7 @@ export async function startGatewayServer(
   ).config;
   const diagnosticsEnabled = isDiagnosticsEnabled(cfgAtStart);
   if (diagnosticsEnabled) {
-    startDiagnosticHeartbeat(cfgAtStart);
+    startDiagnosticHeartbeat();
   }
   setGatewaySigusr1RestartPolicy({ allowExternal: isRestartEnabled(cfgAtStart) });
   setPreRestartDeferralCheck(
diff --git a/src/logging/diagnostic.ts b/src/logging/diagnostic.ts
index ffc36cf98..48f7da84d 100644
--- a/src/logging/diagnostic.ts
+++ b/src/logging/diagnostic.ts
@@ -1,3 +1,4 @@
+import { loadConfig } from "../config/config.js";
 import type { OpenClawConfig } from "../config/config.js";
 import { emitDiagnosticEvent } from "../infra/diagnostic-events.js";
 import {
@@ -325,8 +326,16 @@ export function startDiagnosticHeartbeat(config?: OpenClawConfig) {
   if (heartbeatInterval) {
     return;
   }
-  const stuckSessionWarnMs = resolveStuckSessionWarnMs(config);
   heartbeatInterval = setInterval(() => {
+    let heartbeatConfig = config;
+    if (!heartbeatConfig) {
+      try {
+        heartbeatConfig = loadConfig();
+      } catch {
+        heartbeatConfig = undefined;
+      }
+    }
+    const stuckSessionWarnMs = resolveStuckSessionWarnMs(heartbeatConfig);
     const now = Date.now();
     pruneDiagnosticSessionStates(now, true);
     const activeCount = Array.from(diagnosticSessionStates.values()).filter(