fix(opencode): fix free tier 403 error and improve China region handling

- Force stream:true and cloak decoy tools (bash, read) for OpenCode free tier
- Support connection testing for opencode in testUtils
- Expand error message slice limits in auth and ping to preserve workspace link
- Add concise China region link chip in provider detail page

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

tests/unit/opencode-session.test.js

@@ -276,4 +276,39 @@ describe("OpenCode Stable Session Reuse (429 follow-up)", () => {
     expect(first).toMatch(OPENCODE_SESSION_RE);
     expect(second).toBe(first);
   });
+
+  it("cloaks free-tier requests with bash and read decoy tools", () => {
+    const executor = getExecutor("opencode");
+
+    // Case 1: no tools sent by client -> injects bash + read with tool_choice none
+    const chatNoTools = executor.transformRequest("nemotron-3-ultra-free", {
+      messages: [{ role: "user", content: "hi" }],
+    });
+    expect(chatNoTools.stream).toBe(true);
+    expect(chatNoTools.tool_choice).toBe("none");
+    expect(chatNoTools.tools.map((t) => t.function?.name)).toEqual(["bash", "read"]);
+
+    // Case 2: external CLI tools (e.g. Claude Code Bash) -> preserves Bash, appends read
+    const chatWithTools = executor.transformRequest("nemotron-3-ultra-free", {
+      messages: [{ role: "user", content: "hi" }],
+      tools: [{ type: "function", function: { name: "Bash", description: "Claude Code tool" } }],
+      tool_choice: "auto",
+    });
+    expect(chatWithTools.tool_choice).toBe("auto");
+    const names = chatWithTools.tools.map((t) => t.function?.name);
+    expect(names).toContain("Bash");
+    expect(names).toContain("bash");
+    expect(names).toContain("read");
+
+    // Case 3: already has both bash and read -> do not insert anything
+    const chatFull = executor.transformRequest("nemotron-3-ultra-free", {
+      messages: [{ role: "user", content: "hi" }],
+      tools: [
+        { type: "function", function: { name: "bash", description: "existing" } },
+        { type: "function", function: { name: "read", description: "existing" } },
+      ],
+    });
+    expect(chatFull.tools.length).toBe(2);
+    expect(chatFull.tools[0].function.description).toBe("existing");
+  });
 });