fix: prevent duplicate assistant texts from whitespace differences

- Add per-message dedup tracking in subscribeEmbeddedPiSession
- Compare both trimmed and normalized text to catch near-duplicates
- Reset dedup state on each new assistant message
- Add test for trailing whitespace edge case

Fixes duplicate Slack message delivery when the same text appears
with minor whitespace differences (e.g., trailing newline).

src/agents/pi-embedded-subscribe.handlers.types.ts

@@ -39,6 +39,10 @@ export type EmbeddedPiSubscribeState = {
   lastStreamedAssistant?: string;
   lastStreamedReasoning?: string;
   lastBlockReplyText?: string;
+  assistantMessageIndex: number;
+  lastAssistantTextMessageIndex: number;
+  lastAssistantTextNormalized?: string;
+  lastAssistantTextTrimmed?: string;
   assistantTextBaseline: number;
   suppressBlockChunks: boolean;
   lastReasoningSent?: string;

src/agents/pi-embedded-subscribe.subscribe-embedded-pi-session.does-not-emit-duplicate-block-replies-text.test.ts

@@ -86,6 +86,35 @@ describe("subscribeEmbeddedPiSession", () => {
 
     expect(subscription.assistantTexts).toEqual(["Hello world"]);
   });
+  it("does not duplicate assistantTexts when message_end repeats with trailing whitespace changes", () => {
+    let handler: SessionEventHandler | undefined;
+    const session: StubSession = {
+      subscribe: (fn) => {
+        handler = fn;
+        return () => {};
+      },
+    };
+
+    const subscription = subscribeEmbeddedPiSession({
+      session: session as unknown as Parameters<typeof subscribeEmbeddedPiSession>[0]["session"],
+      runId: "run",
+    });
+
+    const assistantMessageWithNewline = {
+      role: "assistant",
+      content: [{ type: "text", text: "Hello world\n" }],
+    } as AssistantMessage;
+
+    const assistantMessageTrimmed = {
+      role: "assistant",
+      content: [{ type: "text", text: "Hello world" }],
+    } as AssistantMessage;
+
+    handler?.({ type: "message_end", message: assistantMessageWithNewline });
+    handler?.({ type: "message_end", message: assistantMessageTrimmed });
+
+    expect(subscription.assistantTexts).toEqual(["Hello world\n"]);
+  });
   it("does not duplicate assistantTexts when message_end repeats with reasoning blocks", () => {
     let handler: SessionEventHandler | undefined;
     const session: StubSession = {

src/agents/pi-embedded-subscribe.ts

@@ -48,6 +48,10 @@ export function subscribeEmbeddedPiSession(params: SubscribeEmbeddedPiSessionPar
     lastStreamedAssistant: undefined,
     lastStreamedReasoning: undefined,
     lastBlockReplyText: undefined,
+    assistantMessageIndex: 0,
+    lastAssistantTextMessageIndex: -1,
+    lastAssistantTextNormalized: undefined,
+    lastAssistantTextTrimmed: undefined,
     assistantTextBaseline: 0,
     suppressBlockChunks: false, // Avoid late chunk inserts after final text merge.
     lastReasoningSent: undefined,
@@ -84,9 +88,36 @@ export function subscribeEmbeddedPiSession(params: SubscribeEmbeddedPiSessionPar
     state.lastStreamedReasoning = undefined;
     state.lastReasoningSent = undefined;
     state.suppressBlockChunks = false;
+    state.assistantMessageIndex += 1;
+    state.lastAssistantTextMessageIndex = -1;
+    state.lastAssistantTextNormalized = undefined;
+    state.lastAssistantTextTrimmed = undefined;
     state.assistantTextBaseline = nextAssistantTextBaseline;
   };
 
+  const rememberAssistantText = (text: string) => {
+    state.lastAssistantTextMessageIndex = state.assistantMessageIndex;
+    state.lastAssistantTextTrimmed = text.trimEnd();
+    const normalized = normalizeTextForComparison(text);
+    state.lastAssistantTextNormalized = normalized.length > 0 ? normalized : undefined;
+  };
+
+  const shouldSkipAssistantText = (text: string) => {
+    if (state.lastAssistantTextMessageIndex !== state.assistantMessageIndex) return false;
+    const trimmed = text.trimEnd();
+    if (trimmed && trimmed === state.lastAssistantTextTrimmed) return true;
+    const normalized = normalizeTextForComparison(text);
+    if (normalized.length > 0 && normalized === state.lastAssistantTextNormalized) return true;
+    return false;
+  };
+
+  const pushAssistantText = (text: string) => {
+    if (!text) return;
+    if (shouldSkipAssistantText(text)) return;
+    assistantTexts.push(text);
+    rememberAssistantText(text);
+  };
+
   const finalizeAssistantTexts = (args: {
     text: string;
     addedDuringMessage: boolean;
@@ -103,16 +134,15 @@ export function subscribeEmbeddedPiSession(params: SubscribeEmbeddedPiSessionPar
           assistantTexts.length - state.assistantTextBaseline,
           text,
         );
+        rememberAssistantText(text);
       } else {
-        const last = assistantTexts.at(-1);
-        if (!last || last !== text) assistantTexts.push(text);
+        pushAssistantText(text);
       }
       state.suppressBlockChunks = true;
     } else if (!addedDuringMessage && !chunkerHasBuffered && text) {
       // Non-streaming models (no text_delta): ensure assistantTexts gets the final
       // text when the chunker has nothing buffered to drain.
-      const last = assistantTexts.at(-1);
-      if (!last || last !== text) assistantTexts.push(text);
+      pushAssistantText(text);
     }
 
     state.assistantTextBaseline = assistantTexts.length;
@@ -338,8 +368,11 @@ export function subscribeEmbeddedPiSession(params: SubscribeEmbeddedPiSessionPar
       return;
     }
 
+    if (shouldSkipAssistantText(chunk)) return;
+
     state.lastBlockReplyText = chunk;
     assistantTexts.push(chunk);
+    rememberAssistantText(chunk);
     if (!params.onBlockReply) return;
     const splitResult = parseReplyDirectives(chunk);
     const {