Add sequence ID for sorting activities

[compulim]

Fixes #4204.

Changelog Entry

Fixed

• Fixes #4204. Sort using activity.channelData['webchat:sequence-id'] and fallback to epoch time of activity.timestamp, by @compulim, in PR #4203

Description

Today, we use activity.timestamp for sorting activities.

However, in ACS/Omnichannel, the server timestamp has a resolution too low for sorting (up to 1 second).

We are adding activity.channelData['webchat:sequence-id']: number and will use this integer value over activity.timestamp. If not provided, we will fallback to epoch of activity.timestamp.

Design

Please refer to the SORTING.md for design.

Specific Changes

• Clock skew is no longer needed as we are using sequence ID
• Post activity patch activity-in-transit slightly differently
  • Sequence ID is now required internally. For activity-in-transit, we will use the largest sequence ID in the chat history and increase it by 0.001
• activities reducer now use sequence ID for sort keys
• Move activity.channelData.clientTimestamp to activity.localTimestamp
  • clientTimestamp was used for "send failed, retry" prompts, using localTimestamp should have minimal impact
• Fully implemented most types from Direct Line
• Web Chat has a better-defined activity type, namely type WebChatActivity
  • The new type is compatible with type DirectLineActivity but better defined to handle channelData and other Web Chat-specific data structure
  • The new type will be exposed by Web Chat APIs
  • The existing type DirectLineActivity will be used only for communicating with DirectLineJS
• Using import type {} and export type {} over import {} and export default for better tree-shaking

• I have added tests and executed them locally
• I have updated CHANGELOG.md
• I have updated documentation

Review Checklist

This section is for contributors to review your work.

• Accessibility reviewed (tab order, content readability, alt text, color contrast)
• Browser and platform compatibilities reviewed
• CSS styles reviewed (minimal rules, no z-index)
• Documents reviewed (docs, samples, live demo)
• Internationalization reviewed (strings, unit formatting)
• package.json and package-lock.json reviewed
• Security reviewed (no data URIs, check for nonce leak)
• Tests reviewed (coverage, legitimacy)