diff --git a/src/infra/abort-pattern.test.ts b/src/infra/abort-pattern.test.ts
index 6e20d3ce2ba..1bcb7b5bf63 100644
--- a/src/infra/abort-pattern.test.ts
+++ b/src/infra/abort-pattern.test.ts
@@ -1,4 +1,4 @@
-import { describe, expect, it } from "vitest";
+import { describe, expect, it, vi } from "vitest";
 import { bindAbortRelay } from "../utils/fetch-timeout.js";
 
 /**
@@ -25,12 +25,17 @@ describe("abort pattern: .bind() vs arrow closure (#7174)", () => {
   });
 
   it("bound abort works with setTimeout", async () => {
-    const controller = new AbortController();
-    const timer = setTimeout(controller.abort.bind(controller), 10);
-    expect(controller.signal.aborted).toBe(false);
-    await new Promise((r) => setTimeout(r, 50));
-    expect(controller.signal.aborted).toBe(true);
-    clearTimeout(timer);
+    vi.useFakeTimers();
+    try {
+      const controller = new AbortController();
+      const timer = setTimeout(controller.abort.bind(controller), 10);
+      expect(controller.signal.aborted).toBe(false);
+      await vi.advanceTimersByTimeAsync(10);
+      expect(controller.signal.aborted).toBe(true);
+      clearTimeout(timer);
+    } finally {
+      vi.useRealTimers();
+    }
   });
 
   it("bindAbortRelay() preserves default AbortError reason when used as event listener", () => {
diff --git a/src/slack/monitor.test.ts b/src/slack/monitor.test.ts
index 9a1e5e991d0..406b7f2ebac 100644
--- a/src/slack/monitor.test.ts
+++ b/src/slack/monitor.test.ts
@@ -61,29 +61,22 @@ describe("resolveSlackThreadTs", () => {
   const threadTs = "1234567890.123456";
   const messageTs = "9999999999.999999";
 
+  it("stays in incoming threads for all replyToMode values", () => {
+    for (const replyToMode of ["off", "first", "all"] as const) {
+      for (const hasReplied of [false, true]) {
+        expect(
+          resolveSlackThreadTs({
+            replyToMode,
+            incomingThreadTs: threadTs,
+            messageTs,
+            hasReplied,
+          }),
+        ).toBe(threadTs);
+      }
+    }
+  });
+
   describe("replyToMode=off", () => {
-    it("returns incomingThreadTs when in a thread", () => {
-      expect(
-        resolveSlackThreadTs({
-          replyToMode: "off",
-          incomingThreadTs: threadTs,
-          messageTs,
-          hasReplied: false,
-        }),
-      ).toBe(threadTs);
-    });
-
-    it("returns incomingThreadTs even after replies (stays in thread)", () => {
-      expect(
-        resolveSlackThreadTs({
-          replyToMode: "off",
-          incomingThreadTs: threadTs,
-          messageTs,
-          hasReplied: true,
-        }),
-      ).toBe(threadTs);
-    });
-
     it("returns undefined when not in a thread", () => {
       expect(
         resolveSlackThreadTs({
@@ -97,17 +90,6 @@ describe("resolveSlackThreadTs", () => {
   });
 
   describe("replyToMode=first", () => {
-    it("returns incomingThreadTs when in a thread (always stays threaded)", () => {
-      expect(
-        resolveSlackThreadTs({
-          replyToMode: "first",
-          incomingThreadTs: threadTs,
-          messageTs,
-          hasReplied: false,
-        }),
-      ).toBe(threadTs);
-    });
-
     it("returns messageTs for first reply when not in a thread", () => {
       expect(
         resolveSlackThreadTs({
@@ -132,17 +114,6 @@ describe("resolveSlackThreadTs", () => {
   });
 
   describe("replyToMode=all", () => {
-    it("returns incomingThreadTs when in a thread", () => {
-      expect(
-        resolveSlackThreadTs({
-          replyToMode: "all",
-          incomingThreadTs: threadTs,
-          messageTs,
-          hasReplied: false,
-        }),
-      ).toBe(threadTs);
-    });
-
     it("returns messageTs when not in a thread (starts thread)", () => {
       expect(
         resolveSlackThreadTs({