Activity Threads list: implement ListOrganizationThreads (filter/sort/pagination) + participant @nickname enrichment + auth

[rowan-stein]

User request

Implement the Threads-side backend changes to support the Console Activity Threads view moving to server-side filter/sort/pagination with updated authorization.

Source spec: https://github.com/agynio/architecture/blob/main/changes/2026-04-24-activity-server-side-lists.md

Specification (architecture/product)

From:

• changes/2026-04-24-activity-server-side-lists.md
• architecture/threads.md#listorganizationthreads-request-shape
• product/console/console.md (Threads section)

Key requirements:

• New org-scoped list endpoint: ListOrganizationThreads with server-side filter/sort/pagination.
• Deterministic cursor pagination: stable secondary sort by id (ascending); cursor includes tie-breaker.
• List response includes:
  • message_count
  • participants rendered as @NickNames (resolved server-side; client must not do reverse lookup)
• Auth: Threads Activity view is available to org owners + cluster admins (can_view_threads).

Work items

1) Adopt new agynio/api RPC/proto changes

• Update buf.lock and regenerate after agynio/api adds ListOrganizationThreads + Participant.nickname.

2) Implement ListOrganizationThreads

• Add server implementation for the new RPC.
• Filters (combine with AND; *_in values combine with OR):
  • status_in
  • participant_identity_id_in
  • created_after / created_before
• Sort fields: created, updated, message_count, status (+ direction)
• Deterministic cursor pagination:
  • stable tie-breaker by id
  • cursor includes primary sort key + id

3) Participant nickname enrichment

• For each participant identity_id in the list response, populate Participant.nickname.
• Use the new Identity batch/reverse nickname lookup (see agynio/identity + agynio/api issue).

4) Auth enforcement

• Ensure can_view_threads is enforced for org-scoped list.
• Keep existing behavior for other endpoints unless updated by spec.

5) Tests

Add/extend tests to cover:

• filter semantics and pagination reset behavior
• deterministic pagination for each sort
• nickname enrichment behavior (including missing nicknames)
• auth denied cases

Acceptance

• ListOrganizationThreads meets the list-envelope behavior from the spec and is deterministic under pagination.
• Participants include @nickname from server-side enrichment.
• Auth uses can_view_threads.