diff --git a/src/slack/handlers.ts b/src/slack/handlers.ts
index cf90a8514f..26a4e30675 100644
--- a/src/slack/handlers.ts
+++ b/src/slack/handlers.ts
@@ -196,6 +196,13 @@ let cachedBotId: string | null = null;
 const swarmThreadRootCache = new Map<string, boolean>();
 const SWARM_THREAD_ROOT_CACHE_MAX = 1000;
 
+/** Reset Slack handler caches between tests that exercise production handlers. */
+export function resetSlackHandlerCachesForTesting(): void {
+  cachedBotUserId = null;
+  cachedBotId = null;
+  swarmThreadRootCache.clear();
+}
+
 /**
  * Pure check: does the given thread-root message belong to our own swarm bot?
  * Exported for testing.
diff --git a/src/tests/artifact-sdk.test.ts b/src/tests/artifact-sdk.test.ts
index a460be242f..8aaae89912 100644
--- a/src/tests/artifact-sdk.test.ts
+++ b/src/tests/artifact-sdk.test.ts
@@ -9,6 +9,11 @@ import {
 } from "../artifact-sdk/server";
 import { getBasePrompt } from "../prompts/base-prompt";
 
+function restoreEnvValue(key: string, value: string | undefined): void {
+  if (value === undefined) delete process.env[key];
+  else process.env[key] = value;
+}
+
 // ─── Port allocation tests ──────────────────────────────────────────────
 
 describe("getAvailablePort", () => {
@@ -132,9 +137,9 @@ describe("createArtifactServer", () => {
   });
 
   afterAll(() => {
-    process.env.AGENT_ID = originalEnv.AGENT_ID;
-    process.env.API_KEY = originalEnv.API_KEY;
-    process.env.MCP_BASE_URL = originalEnv.MCP_BASE_URL;
+    restoreEnvValue("AGENT_ID", originalEnv.AGENT_ID);
+    restoreEnvValue("API_KEY", originalEnv.API_KEY);
+    restoreEnvValue("MCP_BASE_URL", originalEnv.MCP_BASE_URL);
   });
 
   describe("factory return shape", () => {
@@ -596,9 +601,9 @@ describe("artifact CLI command", () => {
         expect(output).toContain("https://test.lt.example.com");
       } finally {
         console.log = origLog;
-        process.env.MCP_BASE_URL = origEnv.MCP_BASE_URL;
-        process.env.API_KEY = origEnv.API_KEY;
-        process.env.AGENT_ID = origEnv.AGENT_ID;
+        restoreEnvValue("MCP_BASE_URL", origEnv.MCP_BASE_URL);
+        restoreEnvValue("API_KEY", origEnv.API_KEY);
+        restoreEnvValue("AGENT_ID", origEnv.AGENT_ID);
         mockServer.stop();
       }
     });
@@ -627,9 +632,9 @@ describe("artifact CLI command", () => {
         expect(output).toContain("No active artifacts");
       } finally {
         console.log = origLog;
-        process.env.MCP_BASE_URL = origEnv.MCP_BASE_URL;
-        process.env.API_KEY = origEnv.API_KEY;
-        process.env.AGENT_ID = origEnv.AGENT_ID;
+        restoreEnvValue("MCP_BASE_URL", origEnv.MCP_BASE_URL);
+        restoreEnvValue("API_KEY", origEnv.API_KEY);
+        restoreEnvValue("AGENT_ID", origEnv.AGENT_ID);
         mockServer.stop();
       }
     });
@@ -679,9 +684,9 @@ describe("artifact CLI command", () => {
         expect(output).toContain("No active artifacts");
       } finally {
         console.log = origLog;
-        process.env.MCP_BASE_URL = origEnv.MCP_BASE_URL;
-        process.env.API_KEY = origEnv.API_KEY;
-        process.env.AGENT_ID = origEnv.AGENT_ID;
+        restoreEnvValue("MCP_BASE_URL", origEnv.MCP_BASE_URL);
+        restoreEnvValue("API_KEY", origEnv.API_KEY);
+        restoreEnvValue("AGENT_ID", origEnv.AGENT_ID);
         mockServer.stop();
       }
     });
@@ -736,9 +741,9 @@ describe("artifact CLI command", () => {
         expect(output).toContain("stopped");
       } finally {
         console.log = origLog;
-        process.env.MCP_BASE_URL = origEnv.MCP_BASE_URL;
-        process.env.API_KEY = origEnv.API_KEY;
-        process.env.AGENT_ID = origEnv.AGENT_ID;
+        restoreEnvValue("MCP_BASE_URL", origEnv.MCP_BASE_URL);
+        restoreEnvValue("API_KEY", origEnv.API_KEY);
+        restoreEnvValue("AGENT_ID", origEnv.AGENT_ID);
         mockServer.stop();
       }
     });
diff --git a/src/tests/slack-assistant-comention-production.test.ts b/src/tests/slack-assistant-comention-production.test.ts
index 2961c4261e..dad26bf3a9 100644
--- a/src/tests/slack-assistant-comention-production.test.ts
+++ b/src/tests/slack-assistant-comention-production.test.ts
@@ -30,6 +30,7 @@ process.env.SLACK_RENDER_V2 = "false";
 
 let createAssistantFn: typeof import("../slack/assistant").createAssistant;
 let registerMessageHandlerFn: typeof import("../slack/handlers").registerMessageHandler;
+let resetSlackHandlerCachesForTestingFn: typeof import("../slack/handlers").resetSlackHandlerCachesForTesting;
 
 let createTaskWithSiblingAwarenessSpy: any;
 let getAllAgentsSpy: any;
@@ -98,7 +99,11 @@ beforeAll(async () => {
   installSpyImplementations();
 
   ({ createAssistant: createAssistantFn } = await import("../slack/assistant"));
-  ({ registerMessageHandler: registerMessageHandlerFn } = await import("../slack/handlers"));
+  ({
+    registerMessageHandler: registerMessageHandlerFn,
+    resetSlackHandlerCachesForTesting: resetSlackHandlerCachesForTestingFn,
+  } = await import("../slack/handlers"));
+  resetSlackHandlerCachesForTestingFn();
 });
 
 beforeEach(() => {
@@ -120,6 +125,7 @@ afterAll(() => {
   restoreEnvValue("SLACK_ALLOWED_EMAIL_DOMAINS");
   restoreEnvValue("SLACK_ALLOWED_USER_IDS");
   mock.restore();
+  resetSlackHandlerCachesForTestingFn();
 });
 
 // ---------------------------------------------------------------------------