#32118271 Activity Log: Surface MCP client attribution in actor display

Part of https://linear.app/a8c/project/mcp-via-jetpack-activity-log-0c2051df314a/overview

When an activity was performed by an MCP client on a user’s behalf, the API returns is_mcp_agent and mcp_client on the actor object. Propagate these fields through the data layer, types, and all three actor display components so users see ‘via {client} (MCP)’ next to the actor name.

Proposed Changes

• Propagate is_mcp_agent (boolean) and mcp_client (string) from the Activity Streams API actor object through the Calypso data layer (from-api.js, activity-transformer.ts), JSON schema, and all relevant TypeScript types (api-core, state/activity-log, activity-card, Dashboard logs-activity).
• Update the three actor display components — activity-log-item/activity-actor.jsx (classic activity log), activity-card/activity-actor.tsx (backup/clone/activity-log-v2), and dashboard/logs-activity/activity-actor.tsx (Dashboard dataview) — to show a subtle “via {mcp_client} (MCP)” indicator below the actor name when is_mcp_agent is true.
• Add a test case to activity-transformer.test.ts verifying MCP fields are correctly mapped.

Example

Why are these changes being made?

Testing Instructions

• Trigger an activity via an MCP client (e.g. update a post or option through the WordPress.com MCP server using an MCP client like Claude Desktop) and verify the activity log shows “via {client name} (MCP)” beneath the actor name.
• Verify normal (non-MCP) activities still render the actor name and role without any MCP indicator.
• Check the activity log at /activity-log (classic Calypso), the backup search/clone views (uses ActivityCardList), and the Dashboard activity logs — all three should show the MCP indicator for MCP-originated activities.
• Verify the indicator text is subtle (smaller, muted color) and does not disrupt the existing layout.
• Run yarn test-client client/dashboard/sites/logs-activity/test/activity-transformer.test.ts and confirm all 3 tests pass.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you tested accessibility for your changes? Ensure the feature remains usable with various user agents (e.g., browsers), interfaces (e.g., keyboard navigation), and assistive technologies (e.g., screen readers) (PCYsg-S3g-p2).
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
  • For UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• For changes affecting Jetpack: Have we added the “[Status] Needs Privacy Updates” label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?