fix(plugins): read the mem0 CLI key and ignore unexpanded host placeholders

The Python plugin core and the opencode, pi and deepseek plugins now fall back to the key `mem0 init` saves in ~/.mem0/config.json, so a configured CLI is enough to authenticate. The Python core also stops using or caching a literal ${api_key} left behind when a host (Cursor) does not expand its plugin variables, which is what kept asking for auth after the key was set.

Fixes #7346

integrations/pi-agent-plugin/tests/config.test.ts

@@ -1,5 +1,6 @@
 import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
 import * as fs from "node:fs";
+import * as path from "node:path";
 import { loadConfig } from "../src/config/index.ts";
 
 vi.mock("node:fs");
@@ -33,6 +34,17 @@ describe("loadConfig", () => {
     expect(config.apiKey).toBe("");
   });
 
+  it("falls back to the key mem0 init saved", () => {
+    delete process.env.MEM0_API_KEY;
+    vi.mocked(fs.readFileSync).mockImplementation((file) => {
+      if (String(file).endsWith(path.join(".mem0", "config.json"))) {
+        return JSON.stringify({ platform: { api_key: "m0-cli-key" } });
+      }
+      throw new Error("ENOENT");
+    });
+    expect(loadConfig().apiKey).toBe("m0-cli-key");
+  });
+
   it("reads config file and merges with defaults", () => {
     delete process.env.MEM0_API_KEY;
     delete process.env.MEM0_USER_ID;