fix(command-code): include tool call arguments

tests/unit/executor-command-code.test.ts

@@ -56,4 +56,105 @@ describe("CommandCodeExecutor", () => {
       // Network error is expected in test environment
     }
   });
+
+  it("assistant tool-call conversion always emits a valid required arguments field (#regression input[N] missing required field arguments)", async () => {
+    const calls: Array<{ url: string; init: RequestInit; body: unknown }> = [];
+    const originalFetch = globalThis.fetch;
+    globalThis.fetch = (async (url: string | URL | Request, init?: RequestInit) => {
+      calls.push({
+        url: String(url),
+        init: init || {},
+        body: JSON.parse(String((init as RequestInit | undefined)?.body)),
+      });
+      return new Response("", { status: 200 });
+    }) as typeof fetch;
+
+    const executor = new mod.CommandCodeExecutor();
+    const pairedId = "call_paired";
+    const body = {
+      messages: [
+        { role: "user", content: "hi" },
+        {
+          role: "assistant",
+          content: "",
+          tool_calls: [
+            // Missing arguments entirely -> must still get a valid arguments field
+            { id: "call_missing", type: "function", function: { name: "lookup" } },
+            // Empty string arguments -> "{}"
+            {
+              id: "call_empty",
+              type: "function",
+              function: { name: "lookup", arguments: "" },
+            },
+            // Valid object arguments -> round-trips as JSON string
+            {
+              id: pairedId,
+              type: "function",
+              function: { name: "lookup", arguments: { q: "docs" } },
+            },
+            // Valid string arguments -> preserved as-is
+            {
+              id: "call_string",
+              type: "function",
+              function: { name: "lookup", arguments: '{"q":"string"}' },
+            },
+          ],
+        },
+        { role: "tool", tool_call_id: "call_missing", content: "r1" },
+        { role: "tool", tool_call_id: "call_empty", content: "r2" },
+        { role: "tool", tool_call_id: pairedId, content: "r3" },
+        { role: "tool", tool_call_id: "call_string", content: "r4" },
+      ],
+    };
+
+    try {
+      await executor.execute({
+        model: "test",
+        body,
+        stream: false,
+        credentials: { apiKey: "fake-key" },
+        signal: null,
+      });
+      assert.fail("Expected fetch to reject (no real network)");
+    } catch {
+      // Fetch rejection is expected; inspect the captured body
+    } finally {
+      globalThis.fetch = originalFetch;
+    }
+
+    assert.equal(calls.length, 1, "exactly one upstream call");
+    const sentBody = calls[0].body as {
+      params: { messages: Array<{ role: string; content: unknown }> };
+    };
+    const assistant = sentBody.params.messages.find((m) => m.role === "assistant");
+    assert.ok(assistant, "assistant turn present");
+    const parts = assistant.content as Array<Record<string, unknown>>;
+    const toolCalls = parts.filter((p) => p.type === "tool-call");
+    assert.equal(toolCalls.length, 4, "all four paired tool calls converted");
+
+    for (const call of toolCalls) {
+      assert.equal(
+        typeof call.arguments,
+        "string",
+        `tool-call ${String(call.toolCallId)} must carry a string arguments field`
+      );
+      const parsed = JSON.parse(call.arguments as string);
+      assert.equal(typeof parsed, "object");
+      assert.ok(!Array.isArray(parsed), "arguments must parse to a JSON object");
+    }
+
+    const byId = new Map(toolCalls.map((c) => [String(c.toolCallId), c]));
+    assert.equal(byId.get("call_missing").arguments, "{}", "missing arguments -> empty object");
+    assert.equal(byId.get("call_empty").arguments, "{}", "empty string arguments -> empty object");
+    assert.equal(
+      byId.get(pairedId).arguments,
+      '{"q":"docs"}',
+      "object arguments round-trip as JSON string"
+    );
+    assert.equal(
+      byId.get("call_string").arguments,
+      '{"q":"string"}',
+      "valid string arguments preserved as-is"
+    );
+  });
 });