[codex] Split PR #4692 UI/QoL updates (#4701)

## Thinking Path

> - Paperclip orchestrates AI agents through a company-scoped control
plane.
> - The affected surface is the board UI for issue threads, issue lists,
routines, dialogs, navigation, and issue review indicators.
> - Closed PR #4692 bundled backend, schema, docs, workflow, and UI/QoL
work into one oversized change set.
> - Greptile could not keep reviewing that broad PR because it exceeded
the 100-file review limit and mixed unrelated concerns.
> - This pull request extracts the UI/QoL slice into a fresh branch
under the review limit while leaving workflow and lockfile churn out.
> - The benefit is a focused review path for the board UI performance
and workflow improvements without reopening the oversized PR.

## What Changed

- Added long issue-thread virtualization, scroll-container binding,
anchor preservation, latest-comment jump targeting, and related
regression/perf fixtures.
- Improved issue list scalability with scroll-based loading, server
offset parameters, and pagination-focused UI tests.
- Reduced new issue dialog typing churn and split dialog action
subscriptions so broad layout/nav surfaces avoid unnecessary renders.
- Added routine variables help and routine description mention options
for users, agents, and projects.
- Added productivity review badge/link UI and fixed the badge to use
Paperclip's company-prefixed router link.
- Kept the split PR below Greptile's review limit and excluded
`.github/workflows/pr.yml` and `pnpm-lock.yaml`.

## Verification

- `pnpm install --no-frozen-lockfile` in the clean worktree to install
`@tanstack/react-virtual` locally without committing lockfile churn.
- `pnpm --filter @paperclipai/ui exec vitest run --config
vitest.config.ts src/components/IssueChatThread.test.tsx
src/components/IssuesList.test.tsx
src/components/NewIssueDialog.test.tsx src/pages/Routines.test.tsx
src/pages/Issues.test.tsx` passed: 5 files, 83 tests.
- `pnpm --filter @paperclipai/ui typecheck` passed.
- `git diff --check origin/master..HEAD` passed.
- Split-scope checks: 53 changed files; no `.github/workflows/pr.yml`;
no `pnpm-lock.yaml`.
- Screenshots were not captured in this heartbeat; the changes are
primarily virtualization, routing, pagination, and editor behavior
covered by focused regression tests.

## Risks

- Moderate UI risk because issue-thread virtualization changes scroll
behavior on long conversations; regression tests cover anchor jumps,
latest-comment targeting, row metadata, and short-thread fallback.
- Moderate integration risk because the issue-list offset parameter and
productivity review field depend on matching API behavior.
- Dependency risk: the UI package adds `@tanstack/react-virtual` while
repository policy keeps `pnpm-lock.yaml` out of PRs, so CI must resolve
dependency changes through the repo's normal lockfile policy.

> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.

## Model Used

- OpenAI Codex, GPT-5 coding agent, tool-enabled local repository and
GitHub workflow. Exact runtime context window was not exposed by the
harness.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [ ] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

ui/src/pages/Routines.tsx

@@ -7,9 +7,11 @@ import { agentsApi } from "../api/agents";
 import { projectsApi } from "../api/projects";
 import { issuesApi } from "../api/issues";
 import { heartbeatsApi } from "../api/heartbeats";
+import { accessApi } from "../api/access";
 import { useCompany } from "../context/CompanyContext";
 import { useBreadcrumbs } from "../context/BreadcrumbContext";
 import { useToastActions } from "../context/ToastContext";
+import { buildMarkdownMentionOptions } from "../lib/company-members";
 import { queryKeys } from "../lib/queryKeys";
 import { groupBy } from "../lib/groupBy";
 import { createIssueDetailLocationState } from "../lib/issueDetailBreadcrumb";
@@ -23,7 +25,7 @@ import { PageSkeleton } from "../components/PageSkeleton";
 import { PageTabBar } from "../components/PageTabBar";
 import { AgentIcon } from "../components/AgentIconPicker";
 import { InlineEntitySelector, type InlineEntityOption } from "../components/InlineEntitySelector";
-import { MarkdownEditor, type MarkdownEditorRef } from "../components/MarkdownEditor";
+import { MarkdownEditor, type MarkdownEditorRef, type MentionOption } from "../components/MarkdownEditor";
 import {
   RoutineRunVariablesDialog,
   type RoutineRunDialogSubmitData,
@@ -353,6 +355,11 @@ export function Routines() {
     queryFn: () => projectsApi.list(selectedCompanyId!),
     enabled: !!selectedCompanyId,
   });
+  const { data: companyMembers } = useQuery({
+    queryKey: queryKeys.access.companyUserDirectory(selectedCompanyId!),
+    queryFn: () => accessApi.listUserDirectory(selectedCompanyId!),
+    enabled: !!selectedCompanyId,
+  });
   const { data: routineExecutionIssues, isLoading: recentRunsLoading, error: recentRunsError } = useQuery({
     queryKey: [...queryKeys.issues.list(selectedCompanyId!), "routine-executions"],
     queryFn: () => issuesApi.list(selectedCompanyId!, { originKind: "routine_execution" }),
@@ -369,6 +376,14 @@ export function Routines() {
     autoResizeTextarea(titleInputRef.current);
   }, [draft.title, composerOpen]);
 
+  const mentionOptions = useMemo<MentionOption[]>(() => {
+    return buildMarkdownMentionOptions({
+      agents,
+      projects,
+      members: companyMembers?.users,
+    });
+  }, [agents, companyMembers?.users, projects]);
+
   const createRoutine = useMutation({
     mutationFn: () =>
       routinesApi.create(selectedCompanyId!, buildRoutineMutationPayload(draft)),
@@ -808,6 +823,7 @@ export function Routines() {
                 placeholder="Add instructions..."
                 bordered={false}
                 contentClassName="min-h-[160px] text-sm text-muted-foreground"
+                mentions={mentionOptions}
                 onSubmit={() => {
                   if (!createRoutine.isPending && draft.title.trim() && draft.projectId && draft.assigneeAgentId) {
                     createRoutine.mutate();