fix(qq): pin the QQ Music API sidecar to qqMusicApiPort

The embedded QQ Music API sidecar could bind a different port than the one
the client base URL (getQQMusicBaseUrl) targets. The upstream
@sansenjian/qq-music-api package derives its default port from
process.env.PORT (falling back to 3200) and, in some historical versions,
auto-started that server as an import side effect. When an old build listened
on 3300 while the client requested 3200 (issue #122), fetching the QQ login QR
failed with ECONNREFUSED on 127.0.0.1:3200, so the QR never showed and login /
cookie persistence silently broke.

Align process.env.PORT with the configured qqMusicApiPort for the duration of
the import (restoring the previous value afterwards so nothing else in the
process is affected), reuse an already-listening instance instead of racing a
second listen, and log the port actually bound (read from the socket) so any
mismatch is visible in the logs.

- src/music/api-server.ts: PORT alignment + reuse-on-auto-start + bound-port log
- src/music/api-server.test.ts: regression coverage that the sidecar follows
  qqMusicPort (not an injected PORT) and restores PORT afterwards
- README.md: QQ login FAQ clarifies the sidecar and client share qqMusicApiPort
  and points stale-latest-image users (who saw 3300) at re-pulling the image

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/music/api-server.test.ts

@@ -1,5 +1,34 @@
-import { describe, it, expect } from "vitest";
-import { describeQqApiStartupError } from "./api-server.js";
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { createApiServerManager, describeQqApiStartupError } from "./api-server.js";
+import type { Logger } from "../logger.js";
+
+// Record every listen() the QQ sidecar makes so we can assert it is always
+// pinned to the configured port (regression coverage for issue #122).
+const mockState = vi.hoisted(() => ({
+  listenCalls: [] as Array<{ port: number; host: string }>,
+}));
+
+vi.mock("@sansenjian/qq-music-api", () => {
+  const app = {
+    listen(port: number, host: string, cb?: () => void) {
+      mockState.listenCalls.push({ port, host });
+      const server = {
+        address: () => ({ port, address: host, family: "IPv4" as const }),
+        on() {
+          return server;
+        },
+        close(done?: () => void) {
+          done?.();
+        },
+      };
+      // Real net/Koa fire the listening callback on a later tick, after the
+      // caller has captured the returned server handle.
+      if (cb) setImmediate(cb);
+      return server;
+    },
+  };
+  return { default: app };
+});
 
 describe("describeQqApiStartupError", () => {
   it("flags ERR_REQUIRE_ESM by error code with version-pin guidance", () => {
@@ -28,3 +57,77 @@ describe("describeQqApiStartupError", () => {
     expect(describeQqApiStartupError(null)).toBeNull();
   });
 });
+
+// Regression coverage for issue #122: the QQ Music API sidecar must listen on
+// the same port the client base URL targets (config.qqMusicApiPort). A stale
+// build once bound 3300 while the client requested 3200, silently breaking the
+// QQ login QR / search flow with ECONNREFUSED on 127.0.0.1:3200.
+describe("createApiServerManager — QQ sidecar port binding", () => {
+  const noopLogger = {
+    info() {},
+    warn() {},
+    error() {},
+    debug() {},
+    trace() {},
+    fatal() {},
+  } as unknown as Logger;
+
+  beforeEach(() => {
+    mockState.listenCalls = [];
+  });
+
+  it("listens on the configured qqMusicPort and exposes a matching base URL", async () => {
+    const port = 39217; // uncommon port to avoid clashing with a real instance
+    const manager = createApiServerManager(
+      { neteasePort: 39218, qqMusicPort: port, neteaseEnabled: false, qqEnabled: true },
+      noopLogger
+    );
+    await manager.start();
+    manager.stop();
+
+    expect(manager.getQQMusicBaseUrl()).toBe(`http://127.0.0.1:${port}`);
+    expect(mockState.listenCalls).toEqual([{ port, host: "127.0.0.1" }]);
+  });
+
+  it("follows qqMusicPort — not an injected PORT — and restores PORT afterwards", async () => {
+    const port = 39219;
+    const previous = process.env.PORT;
+    // Simulate a hosting platform / compose file injecting a stray PORT that
+    // must NOT leak into the QQ sidecar's chosen port.
+    process.env.PORT = "39999";
+    const manager = createApiServerManager(
+      { neteasePort: 39220, qqMusicPort: port, neteaseEnabled: false, qqEnabled: true },
+      noopLogger
+    );
+    try {
+      await manager.start();
+      // The sidecar follows qqMusicPort, never the injected PORT.
+      expect(mockState.listenCalls).toEqual([{ port, host: "127.0.0.1" }]);
+      // The injected PORT is restored so nothing else in the process is affected.
+      expect(process.env.PORT).toBe("39999");
+    } finally {
+      manager.stop();
+      if (previous === undefined) delete process.env.PORT;
+      else process.env.PORT = previous;
+    }
+  });
+
+  it("leaves an absent PORT env unset after importing the sidecar", async () => {
+    const port = 39221;
+    const previous = process.env.PORT;
+    delete process.env.PORT;
+    const manager = createApiServerManager(
+      { neteasePort: 39222, qqMusicPort: port, neteaseEnabled: false, qqEnabled: true },
+      noopLogger
+    );
+    try {
+      await manager.start();
+      // Was unset before importing — must be unset again, no leaked override.
+      expect(process.env.PORT).toBeUndefined();
+    } finally {
+      manager.stop();
+      if (previous === undefined) delete process.env.PORT;
+      else process.env.PORT = previous;
+    }
+  });
+});

src/music/api-server.ts

@@ -114,7 +114,25 @@ export function createApiServerManager(
             "QQ Music API port already in use — reusing existing instance"
           );
         } else {
-          const qqModule = (await import("@sansenjian/qq-music-api")) as any;
+          // Pin the upstream server to the configured port before importing.
+          // The package derives its default port from process.env.PORT (falling
+          // back to 3200) and, in some historical versions, auto-started that
+          // server as an import side effect. Aligning PORT with qqMusicApiPort
+          // guarantees the sidecar can never bind a different port than the one
+          // the client base URL (getQQMusicBaseUrl) targets — the root cause of
+          // issue #122, where an old build listened on 3300 while the client
+          // requested 3200. Restore the previous value right after import so we
+          // never leak the override into the rest of the process (e.g. the web
+          // server or the NetEase sidecar, which also read PORT as a fallback).
+          const prevPortEnv = process.env.PORT;
+          process.env.PORT = String(options.qqMusicPort);
+          let qqModule: any;
+          try {
+            qqModule = (await import("@sansenjian/qq-music-api")) as any;
+          } finally {
+            if (prevPortEnv === undefined) delete process.env.PORT;
+            else process.env.PORT = prevPortEnv;
+          }
           // The module's export structure varies between versions:
           //   2.2.11+: default → Koa app (has .listen)
           //   2.2.10:  default → wrapper object whose .default is the Koa app
@@ -124,16 +142,34 @@ export function createApiServerManager(
             ? candidate
             : candidate.default ?? null;
           if (koaApp && typeof koaApp.listen === "function") {
-            qqMusicServer = await new Promise<Server>((resolve, reject) => {
-              const srv = koaApp.listen(options.qqMusicPort, "127.0.0.1", () =>
-                resolve(srv)
+            // A version that auto-started on import has already bound the
+            // configured port (thanks to the PORT alignment above); reuse it
+            // rather than racing a second listen that would fail EADDRINUSE.
+            const stillFree = await isPortFree(options.qqMusicPort);
+            if (!stillFree) {
+              logger.info(
+                { port: options.qqMusicPort },
+                "QQ Music API already listening on the configured port (auto-started on import) — reusing embedded instance"
               );
-              srv.on("error", reject);
-            });
-            logger.info(
-              { port: options.qqMusicPort },
-              "QQ Music API started"
-            );
+            } else {
+              qqMusicServer = await new Promise<Server>((resolve, reject) => {
+                const srv = koaApp.listen(options.qqMusicPort, "127.0.0.1", () =>
+                  resolve(srv)
+                );
+                srv.on("error", reject);
+              });
+              // Log the port actually bound (read from the socket) rather than
+              // the requested one, so operators can spot a mismatch in the logs.
+              const addr = qqMusicServer.address();
+              const boundPort =
+                addr && typeof addr === "object" && addr !== null
+                  ? addr.port
+                  : options.qqMusicPort;
+              logger.info(
+                { port: boundPort },
+                "QQ Music API started"
+              );
+            }
           } else {
             logger.warn("QQ Music API module does not expose a Koa app");
           }