fix(combo/fusion): flatten Anthropic-style tool messages in panel calls

flattenToolHistory only recognized OpenAI-style tool calls. Anthropic-compatible clients (Claude Code, /v1/messages) send tool invocations and results as tool_use/tool_result blocks inside the message content array. Since panel calls strip the tools definitions (#1859), the panel expert models received structured tool history without schemas, causing them to fail or misbehave (leading to empty responses and 503 errors).

Extend flattenToolHistory to recognize and flatten tool_use and tool_result blocks in the content array into prose text, keeping panel expert execution robust and independent of the client API format.

PR decolua/9router#1910

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

open-sse/services/combo.js

@@ -31,6 +31,29 @@ function flattenToolHistory(messages) {
         const base = extractTextContent(rest.content) || (typeof rest.content === "string" ? rest.content : "");
         return { ...rest, content: `${base}${base ? "\n" : ""}${TOOL_CALL_PREFIX}${names}]` };
       }
+      if (Array.isArray(msg.content)) {
+        const hasToolUse = msg.content.some((c) => c.type === "tool_use");
+        const hasToolResult = msg.content.some((c) => c.type === "tool_result");
+        if (hasToolUse || hasToolResult) {
+          const textParts = [];
+          const toolNames = [];
+          const toolResults = [];
+          for (const block of msg.content) {
+            if (block.type === "text" && block.text) textParts.push(block.text);
+            if (block.type === "tool_use") toolNames.push(block.name || "tool");
+            if (block.type === "tool_result") toolResults.push(extractTextContent(block.content) || String(block.content ?? ""));
+          }
+          const { ...rest } = msg;
+          let newContent = textParts.join("\n");
+          if (toolNames.length > 0) {
+            newContent = `${newContent}${newContent ? "\n" : ""}${TOOL_CALL_PREFIX}${toolNames.join(", ")}]`;
+          }
+          if (toolResults.length > 0) {
+            newContent = `${newContent}${newContent ? "\n" : ""}${TOOL_RESULT_PREFIX}${toolResults.join("\n")}]`;
+          }
+          return { ...rest, content: newContent };
+        }
+      }
       return msg;
     });
 }

tests/unit/combo-fusion.test.js

@@ -182,4 +182,35 @@ describe("fusion combo", () => {
     expect(judgeBody.messages[1].tool_calls).toBeDefined();
     expect(judgeBody.messages[2].role).toBe("tool");
   });
+
+  it("flattens Anthropic-style tool_use and tool_result blocks in arrays", async () => {
+    const handleSingleModel = vi.fn(async () => okResponse("ans"));
+    await handleFusionChat({
+      body: {
+        messages: [
+          { role: "user", content: "do it" },
+          { role: "assistant", content: [{ type: "text", text: "ok" }, { type: "tool_use", id: "t1", name: "run" }] },
+          { role: "user", content: [{ type: "tool_result", tool_use_id: "t1", content: "done" }] }
+        ],
+        tools: [{ name: "run", description: "d" }]
+      },
+      models: ["p/a", "p/b"],
+      handleSingleModel,
+      log,
+      judgeModel: "p/judge"
+    });
+
+    const panelCalls = handleSingleModel.mock.calls.filter(([,, isPanel]) => isPanel === true);
+    expect(panelCalls.length).toBe(2);
+    const panelBody = panelCalls[0][0];
+    
+    expect(panelBody.tools).toBeUndefined();
+    expect(panelBody.messages.length).toBe(3);
+    
+    // Flattened tool_use
+    expect(panelBody.messages[1].content).toBe("ok\n[Called tools: run]");
+    
+    // Flattened tool_result
+    expect(panelBody.messages[2].content).toBe("[Tool result: done]");
+  });
 });