feat(chat): add sessionId to chat sessions

[mhaack]

Summary

• Adds a sessionId (UUID) to every chat conversation, stored in IndexedDB
  alongside messages so it survives page reloads and is shared across tabs
  on the same room
• New session ID is generated on first open (no existing record) and
  regenerated when the user clears the chat; sent to the agent in every
  POST body so it can scope server-side state per session
• persistence.js updated: loadMessages now returns { messages, sessionId },
  saveMessages accepts sessionId, new resetSession writes empty messages
  • new ID atomically (replaces clearMessages in the reset flow)

Sample Chat message:

{
  "messages": [
    {
      "role": "user",
      "content": "Please summarize the content of this page in a few sentences."
    }
  ],
  "pageContext": {
    "org": "exp-workspace",
    "site": "frescopa",
    "path": "coffee",
    "view": "drafts/hhertach/canvas"
  },
  "imsToken": "....",
  "room": "exp-workspace--frescopa--84361F84631C33D60A495C11@7eeb20f8631c0cb7495c06.e",
  "sessionId": "348c84e6-4eec-4dde-a7c4-7b2583bb194a"
}

URL: https://ew-session--da-nx--adobe.aem.live/

Test Plan

• 8 new unit tests for the persistence layer pass (npx wtr test/nx2/blocks/chat/persistence.test.js --node-resolve)
• Verify IDB record contains sessionId after first message in browser DevTools (Application → IndexedDB → da-chat → conversations)
• Reload page — same sessionId appears in next agent POST (Network tab)
• Open second tab on same URL — same sessionId used
• Click "Clear chat" — new sessionId written to IDB, old one gone

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Commits

• 89ed438 ✅ (latest)
• 88e4190 ✅
• 4091604 ✅
• 1668f16 ✅
• a640658 ✅
• fb9f986 ✅
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• c987df9 ✅
• d0c5a33 ✅

[sharanyavinod]

@mhaack Could you please update docs/chat-ui-component.md to reflect the changes?

[mhaack]

@mhaack Could you please update docs/chat-ui-component.md to reflect the changes?

@sharanyavinod yes good point, done