diff --git a/packages/provider-acp/src/server/runtimeModel.test.ts b/packages/provider-acp/src/server/runtimeModel.test.ts
index 1495d40cc8a1..2ba218d1ce05 100644
--- a/packages/provider-acp/src/server/runtimeModel.test.ts
+++ b/packages/provider-acp/src/server/runtimeModel.test.ts
@@ -66,7 +66,7 @@ describe("AcpRuntimeModel", () => {
     ).toBe(false);
   });
 
-  it("ignores Grok keepalive chunks when tracking session/load replay activity", () => {
+  it("ignores keepalive chunks and untagged metadata when tracking session/load replay activity", () => {
     expect(
       sessionUpdateCountsAsLoadReplayActivity({
         sessionId: "session-1",
@@ -76,6 +76,15 @@ describe("AcpRuntimeModel", () => {
         },
       } satisfies EffectAcpSchema.SessionNotification),
     ).toBe(false);
+    expect(
+      sessionUpdateCountsAsLoadReplayActivity({
+        sessionId: "session-1",
+        update: {
+          sessionUpdate: "available_commands_update",
+          availableCommands: [{ name: "compact", description: "Compact history" }],
+        },
+      } satisfies EffectAcpSchema.SessionNotification),
+    ).toBe(false);
     expect(
       sessionUpdateCountsAsLoadReplayActivity({
         _meta: { isReplay: true },
diff --git a/packages/provider-acp/src/server/runtimeModel.ts b/packages/provider-acp/src/server/runtimeModel.ts
index 454fa3011ed3..b9dcd9590984 100644
--- a/packages/provider-acp/src/server/runtimeModel.ts
+++ b/packages/provider-acp/src/server/runtimeModel.ts
@@ -1282,14 +1282,11 @@ export function sessionUpdateCountsAsLoadReplayActivity(
     case "plan":
     case "plan_update":
     case "plan_removed":
-    case "available_commands_update":
-    case "current_mode_update":
-    case "config_option_update":
-    case "session_info_update":
-    case "usage_update":
     case "compaction_update":
     case "compaction_summary_chunk":
       return true;
+    // Copilot pushes session metadata, then loads for seconds before replaying
+    // untagged history, so metadata must not arm the replay-idle fallback.
     default:
       return false;
   }