fix: strip final tags from session messages

src/agents/session-tool-result-guard.test.ts

@@ -142,4 +142,26 @@ describe("installSessionToolResultGuard", () => {
       .map((e) => (e as { message: AgentMessage }).message);
     expect(messages.map((m) => m.role)).toEqual(["assistant", "toolResult"]);
   });
+
+  it("strips <final> tags from assistant text blocks", () => {
+    const sm = SessionManager.inMemory();
+    installSessionToolResultGuard(sm);
+
+    sm.appendMessage({
+      role: "assistant",
+      content: [
+        { type: "text", text: "<final>Hey!</final>" },
+        { type: "text", text: "More <final>text</final> here." },
+      ],
+    } as AgentMessage);
+
+    const messages = sm
+      .getEntries()
+      .filter((e) => e.type === "message")
+      .map((e) => (e as { message: AgentMessage }).message);
+
+    const assistant = messages[0] as { content?: Array<{ type?: string; text?: string }> };
+    expect(assistant.content?.[0]?.text).toBe("Hey!");
+    expect(assistant.content?.[1]?.text).toBe("More text here.");
+  });
 });

src/agents/session-tool-result-guard.ts

@@ -5,6 +5,39 @@ import { makeMissingToolResult } from "./session-transcript-repair.js";
 
 type ToolCall = { id: string; name?: string };
 
+const FINAL_TAG_RE = /<\s*\/?\s*final\s*>/gi;
+
+function stripFinalTagsFromText(text: string): string {
+  if (!text) return text;
+  return text.replace(FINAL_TAG_RE, "");
+}
+
+function stripFinalTagsFromAssistant(message: Extract<AgentMessage, { role: "assistant" }>) {
+  const content = message.content;
+  if (typeof content === "string") {
+    const cleaned = stripFinalTagsFromText(content);
+    return cleaned === content ? message : ({ ...message, content: cleaned } as AgentMessage);
+  }
+  if (!Array.isArray(content)) return message;
+
+  let changed = false;
+  const next = content.map((block) => {
+    if (!block || typeof block !== "object") return block;
+    const record = block as { type?: unknown; text?: unknown };
+    if (record.type === "text" && typeof record.text === "string") {
+      const cleaned = stripFinalTagsFromText(record.text);
+      if (cleaned !== record.text) {
+        changed = true;
+        return { ...record, text: cleaned };
+      }
+    }
+    return block;
+  });
+
+  if (!changed) return message;
+  return { ...message, content: next } as AgentMessage;
+}
+
 function extractAssistantToolCalls(msg: Extract<AgentMessage, { role: "assistant" }>): ToolCall[] {
   const content = msg.content;
   if (!Array.isArray(content)) return [];
@@ -56,9 +89,13 @@ export function installSessionToolResultGuard(sessionManager: SessionManager): {
       return originalAppend(message as never);
     }
 
+    const sanitized =
+      role === "assistant"
+        ? stripFinalTagsFromAssistant(message as Extract<AgentMessage, { role: "assistant" }>)
+        : message;
     const toolCalls =
       role === "assistant"
-        ? extractAssistantToolCalls(message as Extract<AgentMessage, { role: "assistant" }>)
+        ? extractAssistantToolCalls(sanitized as Extract<AgentMessage, { role: "assistant" }>)
         : [];
 
     // If previous tool calls are still pending, flush before non-tool results.
@@ -70,7 +107,7 @@ export function installSessionToolResultGuard(sessionManager: SessionManager): {
       flushPendingToolResults();
     }
 
-    const result = originalAppend(message as never);
+    const result = originalAppend(sanitized as never);
 
     if (toolCalls.length > 0) {
       for (const call of toolCalls) {