fix(ui): search parent-issue picker on the server (#11334)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work
> - The board UI lets an operator choose a parent issue for an issue
> - The parent picker loads a priority-first page and filters that page
in the browser
> - A medium-priority or low-priority issue past the page limit never
enters the picker
> - This pull request sends typed parent-picker text to the server and
keeps the picker exclusions
> - The benefit is that the operator can select valid parent issues
beyond the default page

## Linked Issues or Issue Description

This pull request supersedes
[#6193](https://github.com/paperclipai/paperclip/pull/6193), whose old
file path no longer matches the current component tree.

**What happened?**

The parent picker fetched one default issue page and filtered it in the
browser. The default page sorts by priority and caps the result at 500
issues. Valid medium-priority and low-priority parent issues beyond that
page stayed hidden.

**Expected behavior**

The parent picker must search the server when the operator types text.
It must show matching issues beyond the default page while it keeps the
current issue and descendant exclusions.

**Steps to reproduce**

1. Open an issue in a company with more than 500 issues.
2. Open the parent picker and type the name of a medium-priority or
low-priority issue beyond the default page.
3. Observe that the picker does not show the matching issue.

**Paperclip version or commit**

Commit `c6965bd0237fd9536b41f1495e2a4bb252afcde7`.

**Deployment mode**

Local dev (`pnpm dev`).

## What Changed

- Send parent-picker searches to the issue list endpoint with `q` and a
bounded `limit` of 50.
- Keep the empty-search list, cycle exclusions, and current sort
behavior.
- Add a component test for a low-priority match hidden by the default
page.

## Verification

- Run `pnpm vitest run ui/src/components/IssueProperties.test.tsx`.
- Confirm that all 53 tests pass.
- Confirm that the new test checks `{ q, limit: 50 }` and the matching
issue.

## Risks

- Low risk. The change affects only parent-picker search requests.
- The server search uses the existing issue list query and does not
change stored data.

## Model Used

Codex, GPT-5, with tool use and code execution. The model assisted with
the change and test.

## 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 searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

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

ui/src/components/IssueProperties.test.tsx

@@ -2039,6 +2039,82 @@ describe("IssueProperties", () => {
 
     act(() => rerenderedRoot.unmount());
   });
+
+  it("searches the server for parent candidates so a lower-priority match past the default page stays selectable", async () => {
+    const onUpdate = vi.fn();
+    // The default list is priority-first and caps at 500 rows, so a low-priority
+    // match past that cap never enters the client list. Model that gap: the default
+    // page returns only a high-priority candidate, and the server search with `q`
+    // returns the low-priority match that the default page hides.
+    const defaultPageCandidate = createIssue({
+      id: "issue-2",
+      identifier: "PAP-2",
+      title: "High priority candidate",
+      status: "in_progress",
+      priority: "high",
+    });
+    const lowPriorityMatch = createIssue({
+      id: "issue-900",
+      identifier: "PAP-900",
+      title: "Low priority needle",
+      status: "todo",
+      priority: "low",
+    });
+    mockIssuesApi.list.mockImplementation((_companyId: string, filters?: { q?: string; limit?: number }) => {
+      if (filters?.q === "needle") return Promise.resolve([lowPriorityMatch]);
+      return Promise.resolve([defaultPageCandidate]);
+    });
+
+    const root = renderProperties(container, {
+      issue: createIssue(),
+      childIssues: [],
+      onUpdate,
+      inline: true,
+    });
+    await flush();
+
+    const parentTrigger = findRowTrigger(container, "Parent");
+    expect(parentTrigger).not.toBeUndefined();
+    await act(async () => {
+      parentTrigger!.dispatchEvent(new MouseEvent("click", { bubbles: true }));
+    });
+    await flush();
+
+    // With an empty search the picker shows the default page. The low-priority match is absent.
+    await waitForAssertion(() => {
+      expect(container.textContent).toContain("PAP-2 High priority candidate");
+    });
+    expect(container.textContent).not.toContain("PAP-900 Low priority needle");
+
+    const searchInput = container.querySelector('input[placeholder="Search tasks..."]') as HTMLInputElement | null;
+    expect(searchInput).not.toBeNull();
+
+    await act(async () => {
+      const nativeSetter = Object.getOwnPropertyDescriptor(HTMLInputElement.prototype, "value")?.set;
+      nativeSetter?.call(searchInput, "needle");
+      searchInput!.dispatchEvent(new Event("input", { bubbles: true }));
+    });
+
+    // The typed text re-queries the server with `q`, and the low-priority match now appears.
+    await waitForAssertion(() => {
+      expect(mockIssuesApi.list).toHaveBeenCalledWith("company-1", { q: "needle", limit: 50 });
+      expect(container.textContent).toContain("PAP-900 Low priority needle");
+      expect(container.textContent).not.toContain("PAP-2 High priority candidate");
+    });
+
+    const candidateButton = Array.from(container.querySelectorAll("button"))
+      .find((button) => button.textContent?.includes("PAP-900 Low priority needle"));
+    expect(candidateButton).not.toBeUndefined();
+
+    await act(async () => {
+      candidateButton!.dispatchEvent(new MouseEvent("click", { bubbles: true }));
+    });
+
+    expect(onUpdate).toHaveBeenCalledWith({ parentId: "issue-900" });
+
+    act(() => root.unmount());
+  });
+
   it("shows a run review action after reviewers are configured and starts execution explicitly when clicked", async () => {
     const onUpdate = vi.fn();
     const root = renderProperties(container, {

ui/src/components/issue-properties/IssueProperties.tsx

@@ -287,6 +287,7 @@ export function IssueProperties({
   const [watchdogAgentInput, setWatchdogAgentInput] = useState(issue.watchdog?.watchdogAgentId ?? "");
   const [watchdogInstructionsInput, setWatchdogInstructionsInput] = useState(issue.watchdog?.instructions ?? "");
   const normalizedBlockedBySearch = blockedBySearch.trim();
+  const normalizedParentSearch = parentSearch.trim();
 
   useEffect(() => {
     setBlockedByExpanded(false);
@@ -349,6 +350,17 @@ export function IssueProperties({
     enabled: !!companyId && blockedByOpen && normalizedBlockedBySearch.length > 0,
   });
 
+  const { data: searchedParentIssues, isFetching: isFetchingSearchedParentIssues } = useQuery({
+    queryKey: companyId
+      ? queryKeys.issues.search(companyId, normalizedParentSearch, undefined, ISSUE_BLOCKER_SEARCH_LIMIT)
+      : ["issues", "blocker-search", normalizedParentSearch, ISSUE_BLOCKER_SEARCH_LIMIT],
+    queryFn: () => issuesApi.list(companyId!, {
+      q: normalizedParentSearch,
+      limit: ISSUE_BLOCKER_SEARCH_LIMIT,
+    }),
+    enabled: !!companyId && parentOpen && normalizedParentSearch.length > 0,
+  });
+
   const createLabel = useMutation({
     mutationFn: (data: { name: string; color: string }) => issuesApi.createLabel(companyId!, data),
     onSuccess: async (created) => {
@@ -1898,22 +1910,22 @@ export function IssueProperties({
       <ArrowUpRight className="h-3 w-3" />
     </Link>
   ) : undefined;
-  const parentOptions = (allIssues ?? [])
+  const parentSearchActive = normalizedParentSearch.length > 0;
+  // When the user types, search on the server. The default list caps at 500 rows
+  // and sorts priority-first, so a medium-priority or low-priority match past that
+  // cap never enters the client list. A server query with `q` still finds it.
+  const parentSourceIssues = parentSearchActive ? searchedParentIssues : allIssues;
+  const parentOptions = (parentSourceIssues ?? [])
     .filter((candidate) => candidate.id !== issue.id)
     .filter((candidate) => !descendantIssueIds.has(candidate.id))
-    .filter((candidate) => {
-      if (!parentSearch.trim()) return true;
-      const query = parentSearch.toLowerCase();
-      return (
-        (candidate.identifier ?? "").toLowerCase().includes(query) ||
-        candidate.title.toLowerCase().includes(query)
-      );
-    })
     .sort((a, b) => {
       const aLabel = `${a.identifier ?? ""} ${a.title}`.trim();
       const bLabel = `${b.identifier ?? ""} ${b.title}`.trim();
       return aLabel.localeCompare(bLabel);
     });
+  const parentOptionsLoading = parentOpen && (
+    parentSearchActive ? isFetchingSearchedParentIssues : isFetchingIssuePickerIssues
+  );
   const parentContent = (
     <>
       <input
@@ -1955,6 +1967,11 @@ export function IssueProperties({
             </span>
           </button>
         ))}
+        {parentOptionsLoading ? (
+          <div className="px-2 py-2 text-xs text-muted-foreground">Searching tasks...</div>
+        ) : parentOptions.length === 0 ? (
+          <div className="px-2 py-2 text-xs text-muted-foreground">No matching tasks.</div>
+        ) : null}
       </div>
     </>
   );