test(translator): add data-driven coverage, bug-exposing cases, and real provider smoke

- matrix.js generates N providers x M models from PROVIDER_MODELS
- coverage-all-models + format-roundtrip for structural/semantic checks
- bugs-* files expose known translation issues via it.fails
- real/smoke-providers runs full handleChatCore path against live providers (RUN_REAL=1), concurrent
- registerAll.js eagerly imports translators (Vitest ESM require fix)
- vitest.config: array aliases for subpaths + maxConcurrency 60

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

tests/translator/bugs-antigravity.test.js

@@ -0,0 +1,54 @@
+// Real Antigravity-MITM requests (Gemini-internal: { request: { contents, ... } }) → OpenAI.
+import { describe, it, expect } from "vitest";
+import "./registerAll.js";
+import { translateRequest } from "../../open-sse/translator/index.js";
+import { FORMATS } from "../../open-sse/translator/formats.js";
+
+const AG2O = (req) =>
+  translateRequest(FORMATS.ANTIGRAVITY, FORMATS.OPENAI, "m", { request: req }, true, null, null);
+
+describe("Antigravity → OpenAI", () => {
+  // antigravity-to-openai.js:177-189 — content with BOTH functionResponse and functionCall/text
+  // returns toolResults early → drops the tool calls / text.
+  // KNOWN BUG
+  it.fails("functionResponse + functionCall in same content keeps both", () => {
+    const out = AG2O({
+      contents: [{
+        role: "model",
+        parts: [
+          { functionResponse: { id: "c1", name: "prev", response: { result: "done" } } },
+          { functionCall: { id: "c2", name: "next", args: {} } },
+        ],
+      }],
+    });
+    const json = JSON.stringify(out);
+    expect(json, "functionCall lost when sharing content with functionResponse").toContain("\"next\"");
+  });
+
+  // antigravity-to-openai.js:167 — functionCall without id gets a random Date.now() id
+  // KNOWN BUG: unstable id breaks matching with its functionResponse
+  it.fails("functionCall without id keeps a stable matchable id", () => {
+    const out = AG2O({
+      contents: [
+        { role: "model", parts: [{ functionCall: { name: "search", args: { q: "x" } } }] },
+        { role: "user", parts: [{ functionResponse: { name: "search", response: { result: "r" } } }] },
+      ],
+    });
+    const asst = out.messages.find((m) => m.tool_calls);
+    const tool = out.messages.find((m) => m.role === "tool");
+    expect(tool?.tool_call_id, "id mismatch between call and response").toBe(asst?.tool_calls?.[0]?.id);
+  });
+
+  // antigravity-to-openai.js:144-147 — signature-only part handling (regression guard)
+  it("signature-only part does not produce empty text", () => {
+    const out = AG2O({
+      contents: [{ role: "model", parts: [{ thoughtSignature: "sig", text: "" }] }],
+    });
+    const asst = out.messages.find((m) => m.role === "assistant");
+    const content = asst?.content;
+    const hasEmpty = Array.isArray(content)
+      ? content.some((c) => c.type === "text" && c.text === "")
+      : content === "";
+    expect(hasEmpty, "empty text part emitted").toBe(false);
+  });
+});