fix(translator): resolve custom provider prefix in debug endpoint

Use getModelInfo instead of parseModel in /api/translator/translate
so custom OpenAI/Anthropic-compatible provider prefixes resolve
correctly, aligning the debug path with the runtime chat path.

Fixes #1083

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

tests/unit/translator-custom-prefix.test.js

@@ -0,0 +1,55 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+// Mock getModelInfo to simulate custom provider prefix resolution
+vi.mock("@/sse/services/model.js", () => ({
+  getModelInfo: vi.fn(async (modelId) => {
+    // Simulate prefix resolution for custom providers
+    if (modelId.startsWith("my-prefix/")) {
+      return {
+        provider: "openai-compatible-chat-abc123",
+        model: modelId.replace("my-prefix/", "")
+      };
+    }
+    if (modelId.startsWith("acme/")) {
+      return {
+        provider: "anthropic-compatible-claude-xyz",
+        model: modelId.replace("acme/", "")
+      };
+    }
+    // Default: no prefix
+    return {
+      provider: modelId.split("/")[1] || "unknown",
+      model: modelId.split("/")[1] || modelId
+    };
+  })
+}));
+
+describe("Translator custom provider prefix resolution", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("should resolve OpenAI-compatible provider prefix via getModelInfo", async () => {
+    const { getModelInfo } = await import("@/sse/services/model.js");
+    const result = await getModelInfo("my-prefix/gpt-4");
+
+    expect(result.provider).toBe("openai-compatible-chat-abc123");
+    expect(result.model).toBe("gpt-4");
+  });
+
+  it("should resolve Anthropic-compatible provider prefix via getModelInfo", async () => {
+    const { getModelInfo } = await import("@/sse/services/model.js");
+    const result = await getModelInfo("acme/claude-3");
+
+    expect(result.provider).toBe("anthropic-compatible-claude-xyz");
+    expect(result.model).toBe("claude-3");
+  });
+
+  it("should handle model ID without prefix", async () => {
+    const { getModelInfo } = await import("@/sse/services/model.js");
+    const result = await getModelInfo("openai/gpt-4");
+
+    expect(result.provider).toBeDefined();
+    expect(result.model).toBe("gpt-4");
+  });
+});