diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7eff14ac382..05c1b0a8748 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -38,6 +38,7 @@ Docs: https://docs.openclaw.ai
 - Control UI/chat: show inline feedback when local slash-command dispatch is unavailable or fails unexpectedly instead of clearing the composer silently. Fixes #52105. Thanks @MooreQiao.
 - Memory/markdown: replace CRLF managed blocks in place and collapse duplicate marker blocks without rewriting unmanaged markdown, so Dreaming and Memory Wiki files self-heal from repeated generated sections. Fixes #75491; supersedes #75495, #75810, and #76008. Thanks @asaenokkostya-coder, @ottodeng, @everettjf, and @lrg913427-dot.
 - Agents/tools: return critical tool-loop circuit-breaker stops as blocked tool results instead of thrown tool failures, so models see the guardrail and stop retrying the same call. Thanks @rayraiser.
+- Agents/sessions: preserve pre-existing runtime model and context window after heartbeat turns so a per-run heartbeat model override does not bleed into shared-session status. Fixes #75452. Thanks @zhang-guiping.
 - Model commands: clarify direct and inline `/model` acknowledgements for non-default selections as session-scoped. Thanks @addu2612.
 - Doctor/gateway: stop warning that non-existent, unconfigured user-bin directories are required in the Gateway service PATH. Fixes #76017. Thanks @xiphis.
 - TUI/chat: skip full provider model normalization during context-window warmup while preserving provider-owned context metadata, avoiding cold-start stalls with large model registries. Thanks @547895019.
diff --git a/src/agents/command/session-store.test.ts b/src/agents/command/session-store.test.ts
index 4fe2908e10d..4e1104eaa6a 100644
--- a/src/agents/command/session-store.test.ts
+++ b/src/agents/command/session-store.test.ts
@@ -931,6 +931,55 @@ describe("updateSessionStoreAfterAgentRun", () => {
     });
   });
 
+  it("leaves contextTokens unset when entry has prior model but no contextTokens (heartbeat bleed guard)", async () => {
+    await withTempSessionStore(async ({ storePath }) => {
+      const cfg = {} as OpenClawConfig;
+      const sessionKey = "agent:main:explicit:test-heartbeat-no-context-tokens";
+      const sessionId = "test-heartbeat-no-context-tokens-session";
+      const sessionStore: Record<string, SessionEntry> = {
+        [sessionKey]: {
+          sessionId,
+          updatedAt: 1,
+          modelProvider: "anthropic",
+          model: "claude-opus-4-6",
+          // contextTokens intentionally missing — older session without cached context
+        },
+      };
+      await fs.writeFile(storePath, JSON.stringify(sessionStore, null, 2));
+
+      // Heartbeat turn uses a different, smaller model
+      const result: EmbeddedPiRunResult = {
+        meta: {
+          durationMs: 500,
+          agentMeta: {
+            sessionId,
+            provider: "ollama",
+            model: "llama3.2:1b",
+            contextTokens: 128_000,
+          },
+        },
+      };
+
+      await updateSessionStoreAfterAgentRun({
+        cfg,
+        sessionId,
+        sessionKey,
+        storePath,
+        sessionStore,
+        defaultProvider: "anthropic",
+        defaultModel: "claude-opus-4-6",
+        result,
+        preserveRuntimeModel: true,
+      });
+
+      // Runtime model should be preserved
+      expect(sessionStore[sessionKey]?.model).toBe("claude-opus-4-6");
+      expect(sessionStore[sessionKey]?.modelProvider).toBe("anthropic");
+      // contextTokens should NOT bleed from the heartbeat run's smaller window
+      expect(sessionStore[sessionKey]?.contextTokens).toBeUndefined();
+    });
+  });
+
   it("falls back to run model when preserveRuntimeModel is true but entry has no prior runtime model", async () => {
     await withTempSessionStore(async ({ storePath }) => {
       const cfg = {} as OpenClawConfig;
diff --git a/src/agents/command/session-store.ts b/src/agents/command/session-store.ts
index 9d7f9add0fd..c14b9e5a6b4 100644
--- a/src/agents/command/session-store.ts
+++ b/src/agents/command/session-store.ts
@@ -120,7 +120,15 @@ export async function updateSessionStoreAfterAgentRun(params: {
     // Keep the pre-existing runtime model and context window so a background
     // heartbeat turn using a different model does not bleed into the main
     // session's perceived state.
-    next.contextTokens = entry.contextTokens ?? contextTokens;
+    if (entry.model) {
+      // Prior runtime model exists: preserve its contextTokens. When missing,
+      // leave contextTokens unset rather than falling back to the heartbeat
+      // run's context window; status derives it from the preserved model.
+      next.contextTokens = entry.contextTokens;
+    } else {
+      // No prior runtime model: heartbeat establishes initial state.
+      next.contextTokens = entry.contextTokens ?? contextTokens;
+    }
     setSessionRuntimeModel(next, {
       provider: entry.modelProvider ?? providerUsed,
       model: entry.model ?? modelUsed,