diff --git a/web/hwlab-cloud-web/scripts/agent-observer-contract.test.ts b/web/hwlab-cloud-web/scripts/agent-observer-contract.test.ts
index 5ef315aa..ae75d83b 100644
--- a/web/hwlab-cloud-web/scripts/agent-observer-contract.test.ts
+++ b/web/hwlab-cloud-web/scripts/agent-observer-contract.test.ts
@@ -27,9 +27,16 @@ test("Agent observer relation tree consumes the YAML node limit", () => {
   assert.equal(window.rows.length, 3);
 });
 
+test("Agent observer relation tree keeps a stable order across live activity reordering", () => {
+  const first = buildRelationWindow([observerRun("run_2"), observerRun("run_1")], null, new Set(), new Set(), 10);
+  const second = buildRelationWindow([observerRun("run_1"), observerRun("run_2")], null, new Set(), new Set(), 10);
+  assert.deepEqual(first.rows.map((row) => row.id), second.rows.map((row) => row.id));
+});
+
 function observerRun(id: string): AgentObserverRun {
   return {
     id,
+    title: null,
     taskId: null,
     taskStatus: null,
     commandId: null,
diff --git a/web/hwlab-cloud-web/src/stores/agent-observer.ts b/web/hwlab-cloud-web/src/stores/agent-observer.ts
index 54245523..bee8376f 100644
--- a/web/hwlab-cloud-web/src/stores/agent-observer.ts
+++ b/web/hwlab-cloud-web/src/stores/agent-observer.ts
@@ -591,7 +591,8 @@ export function buildRelationWindow(
   });
 
   let omittedRunCount = 0;
-  for (const [runIndex, run] of runs.entries()) {
+  const stableRuns = [...runs].sort((left, right) => compareText(relationRunOrderKey(left), relationRunOrderKey(right)));
+  for (const [runIndex, run] of stableRuns.entries()) {
     const hasCompleteContainment = Boolean((run.projectId || run.workspace) && run.sessionId && run.taskId);
     const scopeId = hasCompleteContainment ? relationId("scope", `${run.projectId ?? ""}\u0000${run.workspace ?? ""}`) : unassociatedId;
     const sessionId = hasCompleteContainment && run.sessionId ? relationId("session", `${scopeId}\u0000${run.sessionId}`) : null;
@@ -603,7 +604,7 @@ export function buildRelationWindow(
     const commandId = run.commandId ? relationId("command", `${commandParentId}\u0000${run.commandId}`) : null;
     const missingNodeCount = [scopeId, sessionId, taskId, runNodeId, attemptId, commandId].filter((id): id is string => typeof id === "string" && !nodes.has(id)).length;
     if (nodes.size + missingNodeCount > nodeLimit) {
-      omittedRunCount = runs.length - runIndex;
+      omittedRunCount = stableRuns.length - runIndex;
       break;
     }
     let parent = hasCompleteContainment
@@ -713,6 +714,14 @@ function relationId(kind: AgentObserverRelationKind, value: string): string {
   return `${kind}:${encodeURIComponent(value)}`;
 }
 
+function relationRunOrderKey(run: AgentObserverRun): string {
+  return [run.projectId, run.workspace, run.sessionId, run.taskId, run.id].map((value) => value ?? "").join("\u0000");
+}
+
+function compareText(left: string, right: string): number {
+  return left < right ? -1 : left > right ? 1 : 0;
+}
+
 function latestTimestamp(previous: string | null, next: string | null): string | null {
   if (!previous) return next;
   if (!next) return previous;