feat(agents): show last used by/at on card and settings

[rafavalls]

What is this contribution about?

Surfaces "last used" timestamps for agents on the agent card footer and the agent settings metadata line. Data comes from the most recent thread per agent.

The query lives behind a dedicated read-only tool (VIRTUAL_MCP_LAST_USED_LIST) so it stays off the agent fetch hot path — findById / list on virtual MCPs are unchanged and pay no extra cost.

What changed

Backend

• New tool VIRTUAL_MCP_LAST_USED_LIST (apps/mesh/src/tools/virtual/last-used-list.ts) — takes { ids: string[] }, returns { items: { id, last_used_at?, last_used_by? }[] }. Registered under the existing Basic Usage capability so all org members can read it.
• New ThreadStoragePort.findLastUsedByVirtualMcpIds(orgId, ids) (apps/mesh/src/storage/threads.ts) — single DISTINCT ON (virtual_mcp_id) query against threads, ordered by created_at DESC. Lives next to threads since that's the table queried.
• VirtualMCPEntity schema unchanged — no extra fields on the entity, no extra query when other code paths fetch agents.

SDK

• New hook useVirtualMCPsLastUsed(ids: string[]) in @decocms/mesh-sdk — returns Map<id, { last_used_at?, last_used_by? }>. Disabled when ids is empty. 30s staleTime.

UI

• ProjectCard accepts an optional lastUsedAt?: string prop. Shows "Last used X ago" when set, falls back to "Updated X ago" when no thread exists.
• agents-list.tsx calls the hook once for all visible agents, passes the per-card timestamp down.
• Agent settings page (virtual-mcp/index.tsx) calls the hook for the single agent. Metadata line shows: [avatar] Creator · Created May 6 · Last used X ago (or "Never used").

How to Test

1. Open the agents grid — cards for agents with threads show "Last used X ago" in the footer; cards for agents with no threads show "Updated X ago".
2. Open any agent's settings — the metadata line below the header shows creator + created date + last-used time, or "Never used".
3. Agent fetch endpoints (COLLECTION_VIRTUAL_MCP_GET, COLLECTION_VIRTUAL_MCP_LIST) are unchanged — the threads query only runs when the UI explicitly calls VIRTUAL_MCP_LAST_USED_LIST.

Migration Notes

No database migrations required. The new tool reads from the existing threads table.

Review Checklist

• PR title is clear and descriptive
• Changes are tested and working (`bun test` + `bun run check` pass)
• No breaking changes
• Hot-path agent fetches pay no extra cost

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Release Options

Suggested: Minor (2.311.0) — based on feat: prefix

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Current version: 2.310.11

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