[codex] Improve issue thread review flow (#4381)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - Issue detail is where operators coordinate review, approvals, and
follow-up work with active runs
> - That thread UI needs to surface blockers, descendants, review
handoffs, and reply ergonomics clearly enough for humans to guide agent
work
> - Several small gaps in the issue-thread flow were making review and
navigation clunkier than necessary
> - This pull request improves the reply composer, descendant/blocker
presentation, interaction folding, and review-request handoff plumbing
together as one cohesive issue-thread workflow slice
> - The benefit is a cleaner operator review loop without changing the
broader task model

## What Changed

- restored and refined the floating reply composer behavior in the issue
thread
- folded expired confirmation interactions and improved post-submit
thread scrolling behavior
- surfaced descendant issue context and inline blocker/paused-assignee
notices on the issue detail view
- tightened large-board first paint behavior in `IssuesList`
- added loose review-request handoffs through the issue
execution-policy/update path and covered them with tests

## Verification

- `pnpm vitest run ui/src/pages/IssueDetail.test.tsx`
- `pnpm vitest run server/src/__tests__/issues-service.test.ts
server/src/__tests__/issue-execution-policy.test.ts`
- `pnpm exec vitest run --project @paperclipai/ui
ui/src/components/IssueChatThread.test.tsx
ui/src/components/IssueProperties.test.tsx
ui/src/components/IssuesList.test.tsx ui/src/lib/issue-tree.test.ts
ui/src/api/issues.test.ts`
- `pnpm exec vitest run --project @paperclipai/adapter-utils
packages/adapter-utils/src/server-utils.test.ts`
- `pnpm exec vitest run --project @paperclipai/server
server/src/__tests__/issue-comment-reopen-routes.test.ts -t "coerces
executor handoff patches into workflow-controlled review wakes|wakes the
return assignee with execution_changes_requested"`
- `pnpm exec vitest run --project @paperclipai/server
server/src/__tests__/issue-execution-policy.test.ts
server/src/__tests__/issues-service.test.ts`

## Visual Evidence

- UI layout changes are covered by the focused issue-thread component
and issue-detail tests listed above. Browser screenshots were not
attachable from this automated greploop environment, so reviewers should
use the running preview for final visual confirmation.

## Risks

- Moderate UI-flow risk: these changes touch the issue detail experience
in multiple spots, so regressions would most likely show up as
thread-layout quirks or incorrect review-handoff behavior

> 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-based coding agent with tool use and code execution
in the Codex CLI environment

## 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
- [x] If this change affects the UI, I have included before/after
screenshots or documented the visual verification path
- [ ] 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/lib/issue-tree.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from "vitest";
 import type { Issue } from "@paperclipai/shared";
-import { buildIssueTree, countDescendants } from "./issue-tree";
+import { buildIssueTree, countDescendants, filterIssueDescendants } from "./issue-tree";
 
 function makeIssue(id: string, parentId: string | null = null): Issue {
   return {
@@ -128,3 +128,33 @@ describe("countDescendants", () => {
     expect(countDescendants("nonexistent", childMap)).toBe(0);
   });
 });
+
+describe("filterIssueDescendants", () => {
+  it("returns only children and deeper descendants of the requested root", () => {
+    const root = makeIssue("root");
+    const child = makeIssue("child", "root");
+    const grandchild = makeIssue("grandchild", "child");
+    const unrelatedParent = makeIssue("other");
+    const unrelatedChild = makeIssue("other-child", "other");
+
+    expect(filterIssueDescendants("root", [
+      root,
+      child,
+      grandchild,
+      unrelatedParent,
+      unrelatedChild,
+    ]).map((issue) => issue.id)).toEqual(["child", "grandchild"]);
+  });
+
+  it("handles stale broad issue-list responses without requiring the root in the list", () => {
+    const child = makeIssue("child", "root");
+    const grandchild = makeIssue("grandchild", "child");
+    const globalIssue = makeIssue("global");
+
+    expect(filterIssueDescendants("root", [
+      globalIssue,
+      child,
+      grandchild,
+    ]).map((issue) => issue.id)).toEqual(["child", "grandchild"]);
+  });
+});