refactor(open-sse): D1c — forceStream hardcode → PROVIDERS schema (#5)

chatCore providerRequiresStreaming: switch provider-name →
PROVIDERS[provider].forceStream. Thêm forceStream:true vào registry
openai/codex/commandcode. verify-providers allowlist added-fields
(forceStream/urlSuffix verified bằng golden + runtime test riêng).

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/unit/force-stream-config.test.js

@@ -0,0 +1,17 @@
+// Guards forceStream moved from chatCore hardcode → PROVIDERS schema (#5).
+import { describe, it, expect } from "vitest";
+
+const FORCED = ["openai", "codex", "commandcode"];
+
+describe("forceStream provider config", () => {
+  it("only openai/codex/commandcode force streaming", async () => {
+    const { PROVIDERS } = await import("../../open-sse/config/providers.js");
+    for (const id of FORCED) {
+      expect(PROVIDERS[id]?.forceStream, `${id} forced`).toBe(true);
+    }
+    // a sample of others must NOT force
+    for (const id of ["deepseek", "claude", "gemini", "openrouter"]) {
+      expect(PROVIDERS[id]?.forceStream, `${id} not forced`).not.toBe(true);
+    }
+  });
+});