Summary

Fixes the CodeQL high-severity alert (js/polynomial-redos) that landed on main with #3991.

The alert pointed at packages/core/src/core/openaiContentGenerator/provider/dashscope.ts:44:

```ts
const isDashscopeOrigin =
/([\w-]+.)?dashscope(-intl)?.aliyuncs.com/i.test(normalizedBaseUrl);
```

Two problems with this regex against the user-controlled `baseUrl`:

1. ReDoS surface. `[\w-]+` is a polynomial-backtracking quantifier; combined with the dotted suffix it can take quadratic time on inputs with many `-` characters. `baseUrl` reaches this check unsanitized (env var, settings, CLI flag).
2. Too permissive. The pattern is unanchored and the input is the whole URL (scheme + host + path), so an unrelated host with the dashscope domain in its path — e.g. `https://evil.example/dashscope.aliyuncs.com/...\` — also matches and is treated as a trusted DashScope origin, which causes the client to send the DashScope auth/cache headers + session metadata to a third-party server.

Fix

Parse `baseUrl` with the `URL` constructor and compare the hostname instead. No regex, no ReDoS surface, and strictly tighter:

```ts
let hostname: string | null = null;
try {
hostname = new URL(normalizedBaseUrl).hostname.toLowerCase();
} catch {
hostname = null;
}

const isDashscopeOrigin =
hostname !== null &&
(hostname === 'dashscope.aliyuncs.com' ||
hostname === 'dashscope-intl.aliyuncs.com' ||
hostname.endsWith('.dashscope.aliyuncs.com') ||
hostname.endsWith('.dashscope-intl.aliyuncs.com'));
```

All five existing matching cases (`dashscope.aliyuncs.com`, `dashscope-intl.aliyuncs.com`, `coding.dashscope.aliyuncs.com`, `coding-intl.dashscope-intl.aliyuncs.com`, plus the QWEN_OAUTH / no-baseUrl shortcut) keep passing.

Added three regression tests for the previously-permissive behavior:

• domain appearing only in URL path → false
• `notdashscope.aliyuncs.com` (suffix without dot boundary) → false
• unparseable baseUrl → false

Test plan

• `vitest run packages/core/src/core/openaiContentGenerator/provider/dashscope.test.ts` — 47/47 passing (44 existing + 3 new)
• `eslint` on changed files — clean
• `tsc --noEmit` on `packages/core` — clean
• CodeQL CI on this PR shows the alert resolved