fix: heartbeat prompt + dedupe (#980) (thanks @voidserf)

- tighten default heartbeat prompt guidance
- suppress duplicate heartbeat alerts within 24h

Co-authored-by: void <voidserf@users.noreply.github.com>

src/infra/heartbeat-runner.returns-default-unset.test.ts

@@ -242,6 +242,61 @@ describe("runHeartbeatOnce", () => {
     }
   });
 
+  it("suppresses duplicate heartbeat payloads within 24h", async () => {
+    const tmpDir = await fs.mkdtemp(path.join(os.tmpdir(), "clawdbot-hb-"));
+    const storePath = path.join(tmpDir, "sessions.json");
+    const replySpy = vi.spyOn(replyModule, "getReplyFromConfig");
+    try {
+      const cfg: ClawdbotConfig = {
+        agents: {
+          defaults: {
+            heartbeat: { every: "5m", target: "whatsapp", to: "+1555" },
+          },
+        },
+        channels: { whatsapp: { allowFrom: ["*"] } },
+        session: { store: storePath },
+      };
+      const sessionKey = resolveMainSessionKey(cfg);
+
+      await fs.writeFile(
+        storePath,
+        JSON.stringify(
+          {
+            [sessionKey]: {
+              sessionId: "sid",
+              updatedAt: Date.now(),
+              lastChannel: "whatsapp",
+              lastTo: "+1555",
+              lastHeartbeatText: "Final alert",
+              lastHeartbeatSentAt: 0,
+            },
+          },
+          null,
+          2,
+        ),
+      );
+
+      replySpy.mockResolvedValue([{ text: "Final alert" }]);
+      const sendWhatsApp = vi.fn().mockResolvedValue({ messageId: "m1", toJid: "jid" });
+
+      await runHeartbeatOnce({
+        cfg,
+        deps: {
+          sendWhatsApp,
+          getQueueSize: () => 0,
+          nowMs: () => 60_000,
+          webAuthExists: async () => true,
+          hasActiveWebListener: () => true,
+        },
+      });
+
+      expect(sendWhatsApp).toHaveBeenCalledTimes(0);
+    } finally {
+      replySpy.mockRestore();
+      await fs.rm(tmpDir, { recursive: true, force: true });
+    }
+  });
+
   it("can include reasoning payloads when enabled", async () => {
     const tmpDir = await fs.mkdtemp(path.join(os.tmpdir(), "clawdbot-hb-"));
     const storePath = path.join(tmpDir, "sessions.json");