fix: keep stopped and new prompts separate

.changeset/stop-session-user-message-duplication.md

@@ -0,0 +1,5 @@
+---
+"@jmfederico/pi-web": patch
+---
+
+Keep a new prompt separate from the stopped prompt after aborting a session turn.

src/client/src/chatTranscript.test.ts

@@ -132,6 +132,25 @@ describe("applyTranscriptEvent", () => {
     ]);
   });
 
+  it("does not merge optimistic user messages after an aborted turn", () => {
+    const messages = [textMessage("user", "stopped prompt")];
+
+    expect(applyTranscriptEvent(messages, { type: "message.append", message: { role: "user", content: "new prompt" } })).toEqual([
+      textMessage("user", "stopped prompt"),
+      textMessage("user", "new prompt"),
+    ]);
+  });
+
+  it("replaces a new optimistic user message instead of duplicating it after an aborted turn", () => {
+    let messages: ChatLine[] = [textMessage("user", "stopped prompt")];
+    messages = applyTranscriptEvent(messages, { type: "message.append", message: { role: "user", content: "new prompt" } }) ?? messages;
+
+    expect(applyTranscriptEvent(messages, { type: "message.end", message: { role: "user", content: "new prompt", timestamp: "2026-05-09T12:00:00.000Z" } })).toEqual([
+      textMessage("user", "stopped prompt"),
+      { ...textMessage("user", "new prompt"), meta: { timestamp: "2026-05-09T12:00:00.000Z" } },
+    ]);
+  });
+
   it("replaces an optimistic user message when the finalized text matches", () => {
     const messages = [textMessage("user", "sent prompt")];
 

src/client/src/chatTranscript.ts

@@ -4,7 +4,7 @@ import { appendShellChunk, finalizeShellMessage, shellStartMessage } from "./she
 import type { SessionUiEvent } from "./sessionSocket";
 
 export function applyTranscriptEvent(messages: ChatLine[], event: SessionUiEvent): ChatLine[] | undefined {
-  if (event.type === "message.append") return appendNormalized(messages, event.message);
+  if (event.type === "message.append") return appendNewMessage(messages, event.message);
   if (event.type === "assistant.delta") return appendText(messages, "assistant", event.text);
   if (event.type === "assistant.thinking.delta") return appendThinking(messages, event.text);
   if (event.type === "tool.start") return appendNormalized(messages, { role: "assistant", content: [{ type: "toolCall", name: event.toolName, arguments: event.args }] });
@@ -72,6 +72,11 @@ function messageText(message: ChatLine): string {
     .join("\n\n");
 }
 
+function appendNewMessage(messages: ChatLine[], rawMessage: unknown): ChatLine[] {
+  const lines = normalizeMessage(rawMessage);
+  return lines.length === 0 ? messages : [...messages, ...lines];
+}
+
 function appendNormalized(messages: ChatLine[], rawMessage: unknown): ChatLine[] {
   return normalizeMessage(rawMessage).reduce(appendLine, messages);
 }