fix: prevent history truncation from orphaning tool results

src/agents/pi-embedded-runner.limithistoryturns.test.ts

@@ -154,7 +154,27 @@ describe("limitHistoryTurns", () => {
       { role: "assistant", content: [{ type: "text", text: "response" }] },
     ];
     const limited = limitHistoryTurns(messages, 1);
-    expect(limited[0].content).toEqual([{ type: "text", text: "second" }]);
     expect(limited[1].content).toEqual([{ type: "text", text: "response" }]);
   });
+
+  it("does not slice between tool use and tool result when limit cuts off tool use", () => {
+    const messages: AgentMessage[] = [
+      { role: "user", content: [{ type: "text", text: "start" }] },
+      { role: "assistant", content: [{ type: "text", text: "ack" }] },
+      { role: "user", content: [{ type: "text", text: "do tool" }] },
+      { role: "assistant", content: [{ type: "tool_use", id: "call_1", name: "foo", input: {} }] },
+      { role: "user", content: [{ type: "tool_result", tool_use_id: "call_1", content: "res" }] },
+    ];
+
+    // If we limit to 1 turn, we should get the full tool interaction chain (User -> Asst(Call) -> User(Result))
+    const limited = limitHistoryTurns(messages, 1);
+
+    expect(limited.length).toBe(3);
+    expect(limited[0].role).toBe("user");
+    expect((limited[0].content as any)[0].text).toBe("do tool");
+    expect(limited[1].role).toBe("assistant");
+    expect((limited[1].content as any)[0].type).toBe("tool_use");
+    expect(limited[2].role).toBe("user");
+    expect((limited[2].content as any)[0].type).toBe("tool_result");
+  });
 });

src/agents/pi-embedded-runner/history.ts

@@ -9,9 +9,28 @@ function stripThreadSuffix(value: string): string {
   return match?.[1] ?? value;
 }
 
+/**
+ * Check if a user message is purely a tool result (not a new user turn).
+ */
+function isToolResultMessage(msg: AgentMessage): boolean {
+  if (msg.role !== "user") return false;
+  const content = msg.content;
+  if (!Array.isArray(content)) return false;
+  // A tool result message contains only tool_result blocks
+  return (
+    content.length > 0 &&
+    content.every((block) => {
+      if (!block || typeof block !== "object") return false;
+      const type = (block as { type?: unknown }).type;
+      return type === "tool_result";
+    })
+  );
+}
+
 /**
  * Limits conversation history to the last N user turns (and their associated
  * assistant responses). This reduces token usage for long-running DM sessions.
+ * Tool result messages are not counted as new user turns.
  */
 export function limitHistoryTurns(
   messages: AgentMessage[],
@@ -23,7 +42,9 @@ export function limitHistoryTurns(
   let lastUserIndex = messages.length;
 
   for (let i = messages.length - 1; i >= 0; i--) {
-    if (messages[i].role === "user") {
+    const msg = messages[i];
+    // Only count genuine user messages, not tool results
+    if (msg.role === "user" && !isToolResultMessage(msg)) {
       userCount++;
       if (userCount > limit) {
         return messages.slice(lastUserIndex);