fix(discord): Apply historyLimit to channel/group sessions to prevent compaction bypass (openclaw#11356) thanks @shadril238

Verified:
- pnpm build
- pnpm check
- pnpm test (ran; one unrelated existing failure in models forward-compat test)
- pnpm vitest src/agents/pi-embedded-runner.history-limit-from-session-key.test.ts

Co-authored-by: shadril238 <63901551+shadril238@users.noreply.github.com>
Co-authored-by: Tak Hoffman <781889+Takhoffman@users.noreply.github.com>

src/agents/pi-embedded-runner.history-limit-from-session-key.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, it } from "vitest";
+import type { OpenClawConfig } from "../config/config.js";
+import { getDmHistoryLimitFromSessionKey } from "./pi-embedded-runner.js";
+
+describe("getDmHistoryLimitFromSessionKey", () => {
+  it("keeps backward compatibility for dm/direct session kinds", () => {
+    const config = {
+      channels: { telegram: { dmHistoryLimit: 10 } },
+    } as OpenClawConfig;
+
+    expect(getDmHistoryLimitFromSessionKey("telegram:dm:123", config)).toBe(10);
+    expect(getDmHistoryLimitFromSessionKey("telegram:direct:123", config)).toBe(10);
+  });
+
+  it("returns historyLimit for channel and group session kinds", () => {
+    const config = {
+      channels: { discord: { historyLimit: 12, dmHistoryLimit: 5 } },
+    } as OpenClawConfig;
+
+    expect(getDmHistoryLimitFromSessionKey("discord:channel:123", config)).toBe(12);
+    expect(getDmHistoryLimitFromSessionKey("discord:group:456", config)).toBe(12);
+  });
+
+  it("returns undefined for unsupported session kinds", () => {
+    const config = {
+      channels: { discord: { historyLimit: 12, dmHistoryLimit: 5 } },
+    } as OpenClawConfig;
+
+    expect(getDmHistoryLimitFromSessionKey("discord:slash:123", config)).toBeUndefined();
+  });
+});