Stabilize inline selector keyboard handling (#4617)

## Thinking Path

> - Paperclip's board UI relies on compact selectors for frequent issue
and agent edits.
> - Inline selectors often live inside larger keyboard-aware surfaces
such as composers and popovers.
> - Arrow, enter, tab, and escape keys handled by the selector should
not leak to parent document shortcuts.
> - Stale company selection should also stay hidden until the company
list confirms it is valid.
> - This pull request tightens inline selector keyboard handling and
adds regression coverage for stale company bootstrap behavior.
> - The benefit is fewer accidental parent interactions and safer
company-scoped UI initialization.

## What Changed

- Added a stable empty `recentOptionIds` default so selector filtering
does not get a new array every render.
- Mirrored highlighted option state into a ref so Enter/Tab commits the
current highlighted option reliably after keyboard navigation.
- Stopped propagation for selector-owned navigation/commit/escape keys.
- Added jsdom regressions for inline selector keyboard handling and
CompanyProvider stale selection behavior.

## Verification

- `pnpm exec vitest run ui/src/components/InlineEntitySelector.test.tsx
ui/src/context/CompanyContext.test.tsx`
- Targeted selector and CompanyProvider tests pass cleanly without React
`act(...)` warnings.
- Screenshots not attached: this is keyboard/state behavior covered by
component tests.

## Risks

- Low risk: changes are scoped to inline selector key handling and
tests. The main behavior shift is intentionally preventing handled
selector keys from reaching parent listeners.

> 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 coding agent based on GPT-5, tool-enabled local
repository and shell access, Paperclip heartbeat context.

## 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/components/InlineEntitySelector.test.tsx

@@ -0,0 +1,80 @@
+// @vitest-environment jsdom
+
+import { act } from "react";
+import { createRoot } from "react-dom/client";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { InlineEntitySelector } from "./InlineEntitySelector";
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+(globalThis as any).IS_REACT_ACT_ENVIRONMENT = true;
+
+describe("InlineEntitySelector", () => {
+  let container: HTMLDivElement;
+
+  beforeEach(() => {
+    container = document.createElement("div");
+    document.body.appendChild(container);
+  });
+
+  afterEach(() => {
+    container.remove();
+    document.body.innerHTML = "";
+  });
+
+  it("keeps handled search navigation keys inside the popover", async () => {
+    const root = createRoot(container);
+    const onChange = vi.fn();
+    const documentKeyDown = vi.fn();
+    document.addEventListener("keydown", documentKeyDown);
+
+    act(() => {
+      root.render(
+        <InlineEntitySelector
+          value=""
+          options={[
+            { id: "agent:agent-1", label: "CodexCoder" },
+            { id: "agent:agent-2", label: "DesignBot" },
+          ]}
+          placeholder="Assignee"
+          noneLabel="No assignee"
+          searchPlaceholder="Search assignees..."
+          emptyMessage="No assignees found."
+          onChange={onChange}
+        />,
+      );
+    });
+
+    const trigger = container.querySelector("button") as HTMLButtonElement | null;
+    expect(trigger).not.toBeNull();
+
+    await act(async () => {
+      trigger?.dispatchEvent(new MouseEvent("click", { bubbles: true }));
+    });
+
+    const searchInput = document.querySelector('input[placeholder="Search assignees..."]') as HTMLInputElement | null;
+    expect(searchInput).not.toBeNull();
+    searchInput?.focus();
+
+    await act(async () => {
+      await Promise.resolve();
+    });
+
+    await act(async () => {
+      searchInput?.dispatchEvent(new KeyboardEvent("keydown", { bubbles: true, key: "ArrowDown" }));
+    });
+
+    expect(documentKeyDown).not.toHaveBeenCalled();
+
+    await act(async () => {
+      searchInput?.dispatchEvent(new KeyboardEvent("keydown", { bubbles: true, key: "Enter" }));
+    });
+
+    expect(documentKeyDown).not.toHaveBeenCalled();
+    expect(onChange).toHaveBeenCalledWith("agent:agent-1");
+
+    document.removeEventListener("keydown", documentKeyDown);
+    act(() => {
+      root.unmount();
+    });
+  });
+});