Add Read Receipts and Typing Indicators for ACS Advanced Messaging

[glorialimicrosoft]

🧠 Core Concept:

Message Read Receipts and Typing Indicator Updates are lightweight sent by the business (via ACS) to update the delivery state of a previously received message — such as marking it as read, or indicating the business is typing a response.

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API Change Check

APIView identified API level changes in this PR and created the following API reviews

Language	API Review for Package
Swagger	CallAutomation-Messages
TypeSpec	Azure.Communication.MessagesService
Java	com.azure:azure-communication-messages
JavaScript	@azure-rest/communication-messages
C#	Azure.Communication.Messages

[glorialimicrosoft]

💬 Hero Scenarios: Read Receipt & Typing Indicator in ACS

---

✅ Scenario 1: "Is My Message Seen?" – Customer Support Confirmation

User Story:
As a user texting a business on WhatsApp, I want to know when the business has received and read my message so I don’t feel ignored.

Flow:

1. Customer sends a message to the business WhatsApp account.
2. ACS processes the incoming message.
3. Agent or bot reads the message.
4. Read receipt is sent to WhatsApp via ACS.

Code Example:

POST /messages/readreceipts:send
Content-Type: application/json

{
  "messageId": "d3b54e2e-a723-4b0b-b4bb-162d6506e441",
  "channelRegistrationId": "c987fbc0-1c8f-4ff9-b505-6a7a0d2f1450",
}

---

✅ Scenario 2: "Typing…" – Real-Time Responsiveness Indicator

User Story:
As a customer, I want to see when the agent or bot is actively typing so I know a response is coming soon and don’t exit the conversation.

Flow:

1. Customer sends a message.
2. Bot begins generating a response.
3. Bot sends a read status update with typingIndicator: true.
4. WhatsApp shows the typing bubble.
5. Final response is sent.

Code Example:

POST /messages/readreceipts:send
Content-Type: application/json

{
  "messageId": "6aa0938a-bd77-456b-90b3-11884e61f024",
  "channelRegistrationId": "ee527944-894b-4b58-8b45-b80dc68d6aa1",
  "typingIndicator": true
}

---

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Next Steps to Merge

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[CHILIU-MSFT]

LGTM