diff --git a/src/auto-reply/heartbeat-reply-payload.test.ts b/src/auto-reply/heartbeat-reply-payload.test.ts
index 9d8387c073ed..7c9971113ff3 100644
--- a/src/auto-reply/heartbeat-reply-payload.test.ts
+++ b/src/auto-reply/heartbeat-reply-payload.test.ts
@@ -59,4 +59,15 @@ describe("resolveHeartbeatReplyPayload", () => {
     const blockquoted: ReplyPayload = { text: "Thinking... _weighing the options_" };
     expect(resolveHeartbeatReplyPayload(blockquoted)).toBeUndefined();
   });
+
+  it("skips a trailing lowercase 'reasoning:' payload and returns the final answer", () => {
+    const answer: ReplyPayload = { text: "All clear" };
+    const lowercased: ReplyPayload = { text: "reasoning: because nothing changed" };
+    expect(resolveHeartbeatReplyPayload([answer, lowercased])).toBe(answer);
+  });
+
+  it("returns undefined for a Markdown blockquoted thinking payload", () => {
+    const quoted: ReplyPayload = { text: "> thinking... _weighing the options_" };
+    expect(resolveHeartbeatReplyPayload(quoted)).toBeUndefined();
+  });
 });
diff --git a/src/auto-reply/heartbeat-reply-payload.ts b/src/auto-reply/heartbeat-reply-payload.ts
index ae2c8efb233e..62436347caf8 100644
--- a/src/auto-reply/heartbeat-reply-payload.ts
+++ b/src/auto-reply/heartbeat-reply-payload.ts
@@ -1,39 +1,20 @@
 // Heartbeat reply payload selector for multi-payload auto-reply results.
-import { hasOutboundReplyContent } from "openclaw/plugin-sdk/reply-payload";
+import {
+  hasOutboundReplyContent,
+  isReasoningReplyPayload,
+} from "openclaw/plugin-sdk/reply-payload";
 import type { ReplyPayload } from "./types.js";
 
-// Formatted reasoning prefixes the heartbeat reasoning lane classifies as
-// reasoning even when the `isReasoning` flag is absent: legacy "Reasoning:"
-// text and blockquoted "Thinking..._". Kept in sync with
-// resolveHeartbeatReasoningPayloads (heartbeat-runner) so the selector skips
-// exactly the payloads the reasoning lane delivers separately.
-const FORMATTED_REASONING_PREFIX = /^(?:Reasoning:|Thinking\.{0,3}(?=\s*_))/u;
-
-/** Whether text already carries a formatted reasoning prefix (legacy reasoning). */
-export function hasFormattedReasoningPrefix(text: string): boolean {
-  return FORMATTED_REASONING_PREFIX.test(text.trimStart());
-}
-
-/**
- * Whether a payload is reasoning (flagged or legacy-formatted) and so must not
- * become the user-visible heartbeat reply.
- */
-export function isReasoningReplyPayload(payload: ReplyPayload): boolean {
-  if (payload.isReasoning === true) {
-    return true;
-  }
-  const text = typeof payload.text === "string" ? payload.text : "";
-  return hasFormattedReasoningPrefix(text);
-}
-
 /**
  * Pick the last outbound-capable reply payload for heartbeat delivery.
  *
- * Reasoning payloads are skipped: heartbeat reasoning is delivered separately
- * and only when `includeReasoning` is enabled. Without this guard a trailing
- * reasoning payload (flagged via `isReasoning` or legacy "Reasoning:" /
- * blockquoted "Thinking" text, which reasoning models can emit after the final
- * answer) would be selected as the user-visible heartbeat reply.
+ * Reasoning payloads are skipped using the shared SDK classifier
+ * `isReasoningReplyPayload`, which recognizes the `isReasoning` flag plus the
+ * common reasoning/thinking text prefixes (including lowercased and Markdown
+ * blockquoted forms). Heartbeat reasoning is delivered separately and only when
+ * `includeReasoning` is enabled; without this guard a trailing reasoning
+ * payload (which reasoning models can emit after the final answer) would be
+ * selected as the user-visible heartbeat reply.
  */
 export function resolveHeartbeatReplyPayload(
   replyResult: ReplyPayload | ReplyPayload[] | undefined,
diff --git a/src/infra/heartbeat-runner.ts b/src/infra/heartbeat-runner.ts
index e0965f03051f..bdec9dfb3c56 100644
--- a/src/infra/heartbeat-runner.ts
+++ b/src/infra/heartbeat-runner.ts
@@ -9,6 +9,7 @@ import {
 } from "@openclaw/normalization-core/string-coerce";
 import {
   hasOutboundReplyContent,
+  isReasoningReplyPayload,
   resolveSendableOutboundReplyParts,
 } from "openclaw/plugin-sdk/reply-payload";
 import { normalizeOptionalAgentRuntimeId } from "../agents/agent-runtime-id.js";
@@ -26,11 +27,7 @@ import { resolveAgentHarnessPolicy } from "../agents/harness/policy.js";
 import { resolveModelRefFromString, type ModelRef } from "../agents/model-selection.js";
 import { resolvePersistedSessionRuntimeId } from "../agents/session-runtime-compat.js";
 import { DEFAULT_HEARTBEAT_FILENAME } from "../agents/workspace.js";
-import {
-  hasFormattedReasoningPrefix,
-  isReasoningReplyPayload,
-  resolveHeartbeatReplyPayload,
-} from "../auto-reply/heartbeat-reply-payload.js";
+import { resolveHeartbeatReplyPayload } from "../auto-reply/heartbeat-reply-payload.js";
 import {
   getHeartbeatToolNotificationText,
   resolveHeartbeatToolResponseFromReplyResult,
@@ -757,6 +754,12 @@ function resolveStaleHeartbeatIsolatedSessionKey(params: {
   return undefined;
 }
 
+// Display-format check (not a classifier): whether reasoning text is already
+// rendered in the heartbeat "Reasoning:" / "Thinking..._" form, so it should be
+// delivered as-is rather than re-wrapped by formatReasoningMessage. Reasoning
+// classification itself is the shared SDK `isReasoningReplyPayload`.
+const HEARTBEAT_REASONING_DISPLAY_PREFIX = /^(?:Reasoning:|Thinking\.{0,3}(?=\s*_))/u;
+
 function resolveHeartbeatReasoningPayloads(
   replyResult: ReplyPayload | ReplyPayload[] | undefined,
 ): ReplyPayload[] {
@@ -771,7 +774,9 @@ function resolveHeartbeatReasoningPayloads(
       continue;
     }
 
-    const formattedText = hasFormattedReasoningPrefix(text) ? text : formatReasoningMessage(text);
+    const formattedText = HEARTBEAT_REASONING_DISPLAY_PREFIX.test(text.trimStart())
+      ? text
+      : formatReasoningMessage(text);
     if (!formattedText.trim()) {
       continue;
     }