From 965561eb2206d3f49153e9090feb0364e89bce5f Mon Sep 17 00:00:00 2001
From: local <local>
Date: Sat, 9 May 2026 23:11:53 -0700
Subject: [PATCH] fix(api): type Activity.timestamp/localTimestamp as string,
 not Date
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The Bot Framework Activity protocol sends these as ISO-8601 strings
over JSON (as the existing doc comments already say). Inbound
activities are parsed by express.json() with no reviver and
Activity.from() is just Object.assign — so at runtime these fields
are strings, not Date objects. The Date type was a lie; calling
activity.timestamp.toISOString() in a handler would crash.

The withTimestamp/withLocalTimestamp builders still accept Date for
ergonomics and normalize via toISOString(), so existing call sites
keep working.
---
 packages/api/src/activities/activity.ts | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/packages/api/src/activities/activity.ts b/packages/api/src/activities/activity.ts
index d23162ed1..70b9dd4da 100644
--- a/packages/api/src/activities/activity.ts
+++ b/packages/api/src/activities/activity.ts
@@ -34,7 +34,7 @@ export interface IActivity<T extends string = string> {
   /**
    * Contains the date and time that the message was sent, in UTC, expressed in ISO-8601 format.
    */
-  timestamp?: Date;
+  timestamp?: string;
 
   /**
    * A locale name for the contents of the text field.
@@ -50,7 +50,7 @@ export interface IActivity<T extends string = string> {
    *
    * For example, 2016-09-23T13:07:49.4714686-07:00.
    */
-  localTimestamp?: Date;
+  localTimestamp?: string;
 
   /**
    * Contains an ID that uniquely identifies the channel. Set by the channel.
@@ -138,7 +138,7 @@ export class Activity<T extends string = string> implements IActivity<T> {
   /**
    * Contains the date and time that the message was sent, in UTC, expressed in ISO-8601 format.
    */
-  timestamp?: Date;
+  timestamp?: string;
 
   /**
    * A locale name for the contents of the text field.
@@ -154,7 +154,7 @@ export class Activity<T extends string = string> implements IActivity<T> {
    *
    * For example, 2016-09-23T13:07:49.4714686-07:00.
    */
-  localTimestamp?: Date;
+  localTimestamp?: string;
 
   /**
    * Contains an ID that uniquely identifies the channel. Set by the channel.
@@ -302,8 +302,8 @@ export class Activity<T extends string = string> implements IActivity<T> {
     return this;
   }
 
-  withTimestamp(value: Date) {
-    this.timestamp = value;
+  withTimestamp(value: Date | string) {
+    this.timestamp = value instanceof Date ? value.toISOString() : value;
     return this;
   }
 
@@ -312,8 +312,8 @@ export class Activity<T extends string = string> implements IActivity<T> {
     return this;
   }
 
-  withLocalTimestamp(value: Date) {
-    this.localTimestamp = value;
+  withLocalTimestamp(value: Date | string) {
+    this.localTimestamp = value instanceof Date ? value.toISOString() : value;
     return this;
   }