fix: prevent assistant/reasoning accumulator id collisions (#929)

src/cli/helpers/accumulator.ts

@@ -451,6 +451,18 @@ function extractTextPart(v: unknown): string {
   return "";
 }
 
+function resolveLineIdForKind(
+  b: Buffers,
+  canonicalId: string,
+  kind: "assistant" | "reasoning",
+): string {
+  const existing = b.byId.get(canonicalId);
+  if (!existing || existing.kind === kind) return canonicalId;
+
+  // Avoid cross-kind collisions when providers reuse the same id/otid.
+  return `${kind}:${canonicalId}`;
+}
+
 function resolveAssistantLineId(
   b: Buffers,
   chunk: LettaStreamingResponse & { id?: string; otid?: string },
@@ -499,7 +511,13 @@ function resolveAssistantLineId(
     b.assistantCanonicalByOtid.set(otid, canonical);
   }
 
-  return canonical;
+  const lineId = resolveLineIdForKind(b, canonical, "assistant");
+  if (lineId !== canonical) {
+    if (messageId) b.assistantCanonicalByMessageId.set(messageId, lineId);
+    if (otid) b.assistantCanonicalByOtid.set(otid, lineId);
+  }
+
+  return lineId;
 }
 
 function resolveReasoningLineId(
@@ -549,7 +567,13 @@ function resolveReasoningLineId(
     b.reasoningCanonicalByOtid.set(otid, canonical);
   }
 
-  return canonical;
+  const lineId = resolveLineIdForKind(b, canonical, "reasoning");
+  if (lineId !== canonical) {
+    if (messageId) b.reasoningCanonicalByMessageId.set(messageId, lineId);
+    if (otid) b.reasoningCanonicalByOtid.set(otid, lineId);
+  }
+
+  return lineId;
 }
 
 /**

src/tests/cli/accumulator-usage.test.ts

@@ -237,4 +237,33 @@ describe("accumulator usage statistics", () => {
     expect(line && "text" in line ? line.text : "").toBe("Think through it");
     expect(buffers.byId.get("reasoning-msg-2")).toBeUndefined();
   });
+
+  test("separates reasoning and assistant lines when ids overlap", () => {
+    const buffers = createBuffers();
+
+    onChunk(buffers, {
+      message_type: "reasoning_message",
+      id: "shared-stream-id",
+      reasoning: "Thinking... ",
+    } as unknown as LettaStreamingResponse);
+
+    onChunk(buffers, {
+      message_type: "assistant_message",
+      id: "shared-stream-id",
+      content: [{ type: "text", text: "Final answer" }],
+    } as unknown as LettaStreamingResponse);
+
+    const reasoning = buffers.byId.get("shared-stream-id");
+    const assistant = buffers.byId.get("assistant:shared-stream-id");
+
+    expect(reasoning?.kind).toBe("reasoning");
+    expect(reasoning && "text" in reasoning ? reasoning.text : "").toBe(
+      "Thinking... ",
+    );
+
+    expect(assistant?.kind).toBe("assistant");
+    expect(assistant && "text" in assistant ? assistant.text : "").toBe(
+      "Final answer",
+    );
+  });
 });