fix(activity-feed-v2): load full assignee list when expanding task assignees

[zhirongwang]

Summary

• Tasks with more than 20 assignees only ever displayed the first page returned by the file activities endpoint: the assignee list's "Show more" button expanded the already-loaded entries but never fetched the rest, so the list appeared stuck at 20.
• transformTaskToProps already set hasNextPage from assigned_to.next_marker, but no consumer supplied the onLoadAllAssignee callback that AssigneeList (from @box/activity-feed) needs to fetch the remaining assignees.
• Wire onLoadAllAssignee through ActivityFeedV2 → FeedItemRow → ActivityFeed.List.Task, reusing the existing getTaskCollaborators fetch (/undoc/tasks/{id}/task_collaborators?role=ASSIGNEE&limit=1000) that the task edit modal already uses. This matches the legacy task card's expand behavior (activity-feed/task-new/Task.js).
• Extract the assignee mapping into transformTaskAssignees so the initial transform and the load-all path share the same logic.

Test Plan

• Unit tests added: FeedItemRow passes the original task to onTaskLoadAllAssignees and omits onLoadAllAssignee when no loader is provided; ActivityFeedV2 fetches via getTaskCollaborators and returns transformed assignees, and omits the loader when the prop is absent (all 237 tests in the three touched suites pass)
• tsc and eslint clean
• Verified in Storybook (Elements/ContentSidebar with live token) and in a linked webapp: clicking "Show more" on a 26-assignee task fires the task_collaborators?role=ASSIGNEE&limit=1000 request and renders all 26 assignees with loading state; "Show less" collapses back

Made with Cursor

Summary by CodeRabbit

• New Features
  • Activity feed task rows can now load and display the complete assignee list when more assignees exist beyond the initial preview.
  • Assignee details are rendered consistently, including completed time, status, permissions, and avatars.
• Bug Fixes
  • Improved handling for incomplete/paginated assignee data, with graceful avatar lookup failures and clear error reporting when assignee loading fails.
• Tests
  • Added/extended tests for full assignee loading, avatar URL resolution, and error/no-callback behavior.

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Configuration used: Organization UI

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📥 Commits

Reviewing files that changed from the base of the PR and between e88c508 and 71436a3.

📒 Files selected for processing (1)

• src/elements/content-sidebar/activity-feed-v2/ActivityFeedV2.tsx

🚧 Files skipped from review as they are similar to previous changes (1)

• src/elements/content-sidebar/activity-feed-v2/ActivityFeedV2.tsx

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Walkthrough

Task assignee transformation is extracted into a reusable helper, then connected from ActivityFeedV2 through FeedItemRow to task entries. Tests verify complete-assignee loading, avatar resolution, error propagation, timestamp conversion, callback forwarding, and omission when unavailable.

Changes

Task assignee loading

Layer / File(s)	Summary
Assignee transformation contract src/elements/content-sidebar/activity-feed-v2/transformers.ts	Exports transformTaskAssignees and reuses it from transformTaskToProps to produce normalized assignee props.
Adapter callback wiring src/elements/content-sidebar/activity-feed-v2/ActivityFeedV2.tsx, src/elements/content-sidebar/activity-feed-v2/FeedItemRow.tsx	Fetches complete collaborators through getTaskCollaborators, resolves missing avatars, transforms them, and forwards the loader to task entries.
Assignee loading validation src/elements/content-sidebar/activity-feed-v2/__tests__/*	Verifies pagination flags, transformed collaborator results, avatar fallbacks, callback forwarding, error propagation, and callback omission.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant ActivityFeedListTask
  participant FeedItemRow
  participant ActivityFeedV2
  participant getTaskCollaborators
  ActivityFeedListTask->>FeedItemRow: invoke onLoadAllAssignee(task)
  FeedItemRow->>ActivityFeedV2: invoke onTaskLoadAllAssignees(task)
  ActivityFeedV2->>getTaskCollaborators: fetch complete collaborators
  getTaskCollaborators-->>ActivityFeedV2: return collaborator entries
  ActivityFeedV2-->>ActivityFeedListTask: return transformed assignees

Loading

Possibly related PRs

• box/box-ui-elements#4582: Both changes add full task-assignee loading through getTaskCollaborators.
• box/box-ui-elements#4644: Both modify task-assignee avatar URL handling and transformation.
• box/box-ui-elements#4688: Both modify task-assignee transformation and completion timestamp handling.

Suggested labels: ready-to-merge

Poem

I’m a rabbit with assignees to load,
Hopping callbacks down the code road.
Avatars sparkle, names align,
Tests guard every hop in line.
The full list arrives with care!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly matches the main change: loading the full assignee list when expanding task assignees.
Description check	✅ Passed	The description includes a clear summary and a test plan that covers the implemented behavior and verification steps.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Merge Queue Status

• ✅ Entered queue — 2026-07-26 04:32 UTC · Rule: Automatic strict merge · triggered by rule Automatic merge queue
• ✅ Checks skipped · PR is already up-to-date
• ✅ Merged — 2026-07-26 04:32 UTC · at 71436a33d4a37e7859a57a7230d4c8691556f125 · squash

This pull request spent 9 seconds in the queue, including 1 second running CI.

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