fix(canvas): deduplicate forwarded thread prompts

Generated-By: PostHog Code
Task-Id: 87a79e23-20c4-440b-818b-28154924ffbc

Author: k11kirky

packages/core/src/canvas/threadTimeline.test.ts

@@ -38,6 +38,45 @@ describe("normalizeAgentPromptText", () => {
 });
 
 describe("buildThreadTimeline", () => {
+  it("omits the session echo of a forwarded thread message", () => {
+    const timeline = buildThreadTimeline({
+      prompts: [
+        {
+          id: "prompt",
+          text: "[Thread comment from Peter Kirkham] @agent which model are you?",
+          timestamp: 200,
+        },
+      ],
+      humanMessages: [
+        {
+          id: "human",
+          content: "@agent which model are you?",
+          createdAt: "1970-01-01T00:00:00.100Z",
+          forwardedToAgent: true,
+        },
+      ],
+      agentMessages: [],
+    });
+
+    expect(timeline.map((row) => row.kind)).toEqual(["human"]);
+  });
+
+  it("keeps a thread-comment prompt without a matching forwarded message", () => {
+    const timeline = buildThreadTimeline({
+      prompts: [
+        {
+          id: "prompt",
+          text: "[Thread comment from Peter Kirkham] @agent which model are you?",
+          timestamp: 200,
+        },
+      ],
+      humanMessages: [],
+      agentMessages: [],
+    });
+
+    expect(timeline.map((row) => row.kind)).toEqual(["prompt"]);
+  });
+
   it("interleaves prompts, human replies, and agent turns chronologically", () => {
     const timeline = buildThreadTimeline({
       prompts: [{ id: "prompt", text: "Start", timestamp: 100 }],

packages/core/src/canvas/threadTimeline.ts

@@ -8,6 +8,7 @@ export interface ThreadHumanMessage<T = unknown> {
   id: string;
   content: string;
   createdAt: string;
+  forwardedToAgent?: boolean;
   value?: T;
 }
 
@@ -36,8 +37,19 @@ export function buildThreadTimeline<T>({
   agentMessages: ThreadAgentMessage[];
   humanMessages: ThreadHumanMessage<T>[];
 }): ThreadTimelineRow<T>[] {
+  const forwardedHumanContent = new Set(
+    humanMessages
+      .filter((message) => message.forwardedToAgent)
+      .map((message) => normalizeAgentPromptText(message.content)),
+  );
+  const visiblePrompts = prompts.filter(
+    (message) =>
+      !isThreadCommentPrompt(message.text) ||
+      !forwardedHumanContent.has(normalizeAgentPromptText(message.text)),
+  );
+
   return [
-    ...prompts.map(
+    ...visiblePrompts.map(
       (message): ThreadTimelineRow<T> => ({
         kind: "prompt",
         timestamp: validTimestamp(message.timestamp),
@@ -85,6 +97,10 @@ export function normalizeAgentPromptText(content: string): string {
     .trim();
 }
 
+function isThreadCommentPrompt(content: string): boolean {
+  return THREAD_COMMENT_ATTRIBUTION_PATTERN.test(content.trim());
+}
+
 export function deriveThreadAgentStatus({
   hasActivity = false,
   hasError = false,

packages/ui/src/features/canvas/components/ThreadPanel.tsx

@@ -415,6 +415,7 @@ function ThreadConversation({
           id: message.id,
           content: message.content,
           createdAt: message.created_at,
+          forwardedToAgent: !!message.forwarded_to_agent_at,
           value: message,
         })),
       }),