fix(translator): shape Anthropic non-stream responses from forced-streaming providers

The non-streaming Anthropic path leaked OpenAI chat.completion bodies to
Claude clients when the upstream provider forces streaming (forced
SSE->JSON path): parseSSEToOpenAIResponse yields choices[] which Claude
Code cannot parse. Convert to Claude Messages shape for sourceFormat
CLAUDE in sseToJsonHandler.

Shared toClaudeMessageShape/openAICompletionToClaudeMessage moved to
translator/concerns/claudeShape.js to avoid circular import between
nonStreamingHandler and sseToJsonHandler. 5 new tests: sse-to-json
reassembly + Claude guard, plus existing anthropic-nonstream-shape
updated to import from the concern.

tests/unit/anthropic-nonstream-shape.test.js

@@ -1,7 +1,7 @@
 import { describe, expect, it } from "vitest";
 
 const { stripEosSentinel } = await import("../../open-sse/translator/concerns/eosStrip.js");
-const { toClaudeMessageShape } = await import("../../open-sse/handlers/chatCore/nonStreamingHandler.js");
+const { toClaudeMessageShape } = await import("../../open-sse/translator/concerns/claudeShape.js");
 
 // An OpenAI-shape body as returned by a claude-transport executor (opencode/
 // big-pickle): no type:"message", choices[] present. This is what an Anthropic

tests/unit/sse-to-json-claude-shape.test.js

@@ -0,0 +1,54 @@
+import { describe, expect, it } from "vitest";
+
+const { parseSSEToOpenAIResponse } = await import("../../open-sse/handlers/chatCore/sseToJsonHandler.js");
+const { toClaudeMessageShape } = await import("../../open-sse/translator/concerns/claudeShape.js");
+
+// SSE fixture of an OpenAI chat streaming provider (eg big-pickle forced
+// streaming): text deltas + reasoning + tool_calls + usage.
+const OPENAI_SSE = [
+  "data: {\"id\":\"chatcmpl-abc\",\"object\":\"chat.completion.chunk\",\"created\":1000,\"model\":\"big-pickle\",\"choices\":[{\"index\":0,\"delta\":{\"role\":\"assistant\",\"content\":\"\",\"reasoning_content\":\"let me think\"},\"finish_reason\":null}]}",
+  "data: {\"id\":\"chatcmpl-abc\",\"object\":\"chat.completion.chunk\",\"created\":1000,\"model\":\"big-pickle\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"Hel\"},\"finish_reason\":null}]}",
+  "data: {\"id\":\"chatcmpl-abc\",\"object\":\"chat.completion.chunk\",\"created\":1000,\"model\":\"big-pickle\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"lo\"},\"finish_reason\":null}]}",
+  "data: {\"id\":\"chatcmpl-abc\",\"object\":\"chat.completion.chunk\",\"created\":1000,\"model\":\"big-pickle\",\"choices\":[{\"index\":0,\"delta\":{\"tool_calls\":[{\"index\":0,\"id\":\"call_1\",\"function\":{\"name\":\"get_weather\",\"arguments\":\"{\\\"city\\\":\\\"Jakarta\\\"}\"}}]},\"finish_reason\":null}]}",
+  "data: {\"id\":\"chatcmpl-abc\",\"object\":\"chat.completion.chunk\",\"created\":1000,\"model\":\"big-pickle\",\"choices\":[{\"index\":0,\"delta\":{},\"finish_reason\":\"tool_calls\"}],\"usage\":{\"prompt_tokens\":10,\"completion_tokens\":20,\"total_tokens\":30}}",
+  "data: [DONE]"
+].join("\n");
+
+describe("parseSSEToOpenAIResponse (forced streaming → JSON)", () => {
+  it("reassembles content, reasoning, tool_calls, finish_reason, usage", () => {
+    const parsed = parseSSEToOpenAIResponse(OPENAI_SSE, "big-pickle");
+    expect(parsed.object).toBe("chat.completion");
+    expect(parsed.choices[0].message.content).toBe("Hello");
+    expect(parsed.choices[0].message.reasoning_content).toBe("let me think");
+    expect(parsed.choices[0].message.tool_calls).toHaveLength(1);
+    expect(parsed.choices[0].message.tool_calls[0].function.name).toBe("get_weather");
+    expect(parsed.choices[0].message.tool_calls[0].function.arguments).toContain("Jakarta");
+    expect(parsed.choices[0].finish_reason).toBe("tool_calls");
+    expect(parsed.usage.total_tokens).toBe(30);
+  });
+
+  it("returns null for empty / malformed SSE", () => {
+    expect(parseSSEToOpenAIResponse("", "m")).toBeNull();
+    expect(parseSSEToOpenAIResponse("data: [DONE]", "m")).toBeNull();
+  });
+});
+
+describe("sseToJson Anthropic guard (sourceFormat=CLAUDE)", () => {
+  it("converts parsed OpenAI body to Claude message shape", () => {
+    const parsed = parseSSEToOpenAIResponse(OPENAI_SSE, "big-pickle");
+    const out = toClaudeMessageShape(parsed);
+
+    expect(out.type).toBe("message");
+    expect(out.role).toBe("assistant");
+    expect(Array.isArray(out.content)).toBe(true);
+    expect(out.content[0].type).toBe("thinking");
+    expect(out.content[0].thinking).toBe("let me think");
+    expect(out.content[1].type).toBe("text");
+    expect(out.content[1].text).toBe("Hello");
+    expect(out.content[2].type).toBe("tool_use");
+    expect(out.content[2].name).toBe("get_weather");
+    expect(out.stop_reason).toBe("tool_use");
+    expect(out.usage.input_tokens).toBe(10);
+    expect(out.usage.output_tokens).toBe(20);
+  });
+});