feat: tambah DSML parser untuk konversi tool_calls DeepSeek ke format standar

DeepSeek models mengembalikan tool calls dalam format DSML (DeepSeek
Markup Language) di dalam text content, bukan sebagai JSON structured
tool_calls. Ini menyebabkan tool calling gagal di Claude Code.

Perubahan:
- Buat src/lib/dsml-parser.ts: parser DSML berbasis regex dengan dukungan
  streaming (DSMLAccumulator), deteksi teks sebelum/sesudah DSML, dan
  parsing parameter JSON
- Forward tools/tool_choice dari client ke backend di Anthropic & OpenAI paths
- Konversi DSML ke tool_use content blocks (Anthropic) atau tool_calls array
  (OpenAI) di response non-streaming
- Handle DSML di streaming: buffer text deltas, deteksi di akhir stream,
  emit tool_use/tool_calls events yang sesuai
- Handle tool_result blocks dari Anthropic format di assistant messages
- Tambah 29 tests untuk parser dan 18 tests untuk anthropic-proxy

Fix: #285 tests pass, 0 fail
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/anthropic-proxy.test.ts

@@ -1,5 +1,5 @@
 import { test, expect, describe } from "bun:test";
-import { anthropicToBackend } from "./anthropic-proxy";
+import { anthropicToBackend, backendToAnthropicResponse, generateToolUseId } from "./anthropic-proxy";
 import type { BackendConfig } from "./ai-proxy";
 
 const passthroughConfig: BackendConfig = {
@@ -216,4 +216,138 @@ describe("anthropicToBackend", () => {
 		expect(body.messages[0].role).toBe("system");
 		expect(body.messages[0].content).toBe("You are a helpful assistant.");
 	});
+
+	test("should forward tools in request body", () => {
+		const result = anthropicToBackend(
+			{
+				model: "deepseek-v4-flash-free",
+				max_tokens: 100,
+				messages: [{ role: "user", content: "Hi" }],
+				tools: [{ name: "test_tool", input_schema: { type: "object" } }],
+			},
+			passthroughConfig,
+			"deepseek-v4-flash-free",
+		);
+		const body = result.body as any;
+		expect(body.tools).toBeDefined();
+		expect(body.tools).toHaveLength(1);
+		expect(body.tools[0].name).toBe("test_tool");
+	});
+
+	test("should forward tool_choice in request body", () => {
+		const result = anthropicToBackend(
+			{
+				model: "deepseek-v4-flash-free",
+				max_tokens: 100,
+				messages: [{ role: "user", content: "Hi" }],
+				tool_choice: { type: "tool", name: "test_tool" },
+			},
+			passthroughConfig,
+			"deepseek-v4-flash-free",
+		);
+		const body = result.body as any;
+		expect(body.tool_choice).toBeDefined();
+		expect(body.tool_choice.type).toBe("tool");
+	});
+});
+
+describe("backendToAnthropicResponse", () => {
+	test("should convert plain text to text content block", () => {
+		const raw = {
+			id: "test_1",
+			choices: [{ message: { content: "Hello world" }, finish_reason: "stop" }],
+			usage: { prompt_tokens: 10, completion_tokens: 20 },
+		};
+		const result = backendToAnthropicResponse(raw, "deepseek-v4-flash-free");
+		expect(result.content).toHaveLength(1);
+		expect(result.content[0].type).toBe("text");
+		expect((result.content[0] as any).text).toBe("Hello world");
+		expect(result.stop_reason).toBe("end_turn");
+	});
+
+	test("should convert DSML to tool_use content blocks", () => {
+		const raw = {
+			id: "test_2",
+			choices: [{
+				message: { content: `<tool_calls>
+<invoke name="Bash">
+<parameter name="command">ls -la</parameter>
+</invoke>
+</tool_calls>` },
+				finish_reason: "stop",
+			}],
+			usage: { prompt_tokens: 10, completion_tokens: 20 },
+		};
+		const result = backendToAnthropicResponse(raw, "deepseek-v4-flash-free");
+		expect(result.content).toHaveLength(1);
+		expect(result.content[0].type).toBe("tool_use");
+		const toolUse = result.content[0] as any;
+		expect(toolUse.name).toBe("Bash");
+		expect(toolUse.input.command).toBe("ls -la");
+		expect(toolUse.id).toBeTruthy();
+		expect(result.stop_reason).toBe("tool_use");
+	});
+
+	test("should convert text before DSML as separate text block", () => {
+		const raw = {
+			id: "test_3",
+			choices: [{
+				message: { content: "Let me check.\n<tool_calls>\n<invoke name=\"Read\">\n<parameter name=\"path\">/tmp/test</parameter>\n</invoke>\n</tool_calls>" },
+				finish_reason: "stop",
+			}],
+			usage: { prompt_tokens: 5, completion_tokens: 15 },
+		};
+		const result = backendToAnthropicResponse(raw, "deepseek-v4-flash-free");
+		expect(result.content).toHaveLength(2);
+		expect(result.content[0].type).toBe("text");
+		expect(((result.content[0] as any).text).trim()).toBe("Let me check.");
+		expect(result.content[1].type).toBe("tool_use");
+		expect((result.content[1] as any).name).toBe("Read");
+	});
+
+	test("should handle multiple tool calls in DSML", () => {
+		const raw = {
+			id: "test_4",
+			choices: [{
+				message: { content: `<tool_calls>
+<invoke name="Bash">
+<parameter name="command">ls</parameter>
+</invoke>
+<invoke name="Read">
+<parameter name="file_path">test.txt</parameter>
+</invoke>
+</tool_calls>` },
+				finish_reason: "stop",
+			}],
+			usage: { prompt_tokens: 5, completion_tokens: 15 },
+		};
+		const result = backendToAnthropicResponse(raw, "deepseek-v4-flash-free");
+		expect(result.content).toHaveLength(2);
+		expect(result.content[0].type).toBe("tool_use");
+		expect((result.content[0] as any).name).toBe("Bash");
+		expect(result.content[1].type).toBe("tool_use");
+		expect((result.content[1] as any).name).toBe("Read");
+	});
+
+	test("should return plain text when no DSML in response", () => {
+		const raw = {
+			id: "test_5",
+			choices: [{ message: { content: "Hello" }, finish_reason: "stop" }],
+			usage: { prompt_tokens: 5, completion_tokens: 10 },
+		};
+		const result = backendToAnthropicResponse(raw, "deepseek-v4-flash-free");
+		expect(result.content).toHaveLength(1);
+		expect(result.content[0].type).toBe("text");
+		expect(result.stop_reason).toBe("end_turn");
+	});
+});
+
+describe("generateToolUseId", () => {
+	test("should generate unique IDs with toolu_ prefix", () => {
+		const id1 = generateToolUseId();
+		const id2 = generateToolUseId();
+		expect(id1).toMatch(/^toolu_/);
+		expect(id2).toMatch(/^toolu_/);
+		expect(id1).not.toBe(id2);
+	});
 });