Fix disappearing issue comments (#4557)

## Thinking Path

> - Paperclip is a control plane for AI-agent companies, so issue detail
pages are a primary surface for understanding agent work and human
feedback.
> - The relevant subsystem here is the issue comments/chat experience
across the React issue detail page and the server comment pagination
API.
> - Long issue threads were only surfacing the newest page of comments
at first render, which hid earlier human and agent messages behind extra
pagination.
> - The first UI fix exposed that the descending cursor path on the
server could also fail for older-page fetches, leaving the chat tab
stuck on an infinite "Loading earlier comments..." state.
> - This needed to be addressed in both layers so the chat tab can
surface earlier conversation history without manual recovery and without
server errors.
> - This pull request auto-loads earlier comment pages in the issue
detail chat view and fixes the descending cursor predicate used by issue
comment pagination.
> - The benefit is that long-running issues like `PAPA-103` now show the
missing conversation history near the top of the chat surface instead of
hiding it or failing to load it.

## What Changed

- Auto-load earlier issue comment pages in the issue detail chat tab
until the thread reaches a 150-comment cap or there are no older
comments left.
- Add UI-side guard logic and regression coverage for optimistic issue
comment pagination so the autoload behavior stops cleanly.
- Replace the raw SQL descending cursor predicate in
`issueService.listComments` with typed Drizzle comparisons for the
`(createdAt, id)` anchor tuple.
- Add a server regression test that paginates earlier comments in
descending order from an anchor comment.
- Smoke-test the exact previously failing seeded `PAPA-103` cursor path
on the isolated dev instance used for review.

## Verification

- `pnpm --filter @paperclipai/server exec vitest run
src/__tests__/issues-service.test.ts`
- `pnpm --filter @paperclipai/server typecheck`
- Manual smoke against seeded `PAPA-103` data on the isolated dev
server:
- `GET /api/issues/PAPA-103/comments?order=desc&limit=50` returns `200`
- `GET
/api/issues/PAPA-103/comments?after=765d3609-edc6-4d11-a8fe-d466affbe85d&order=desc&limit=50`
now returns `200` with 50 comments instead of `500`

## Risks

- Moderate UI/perf risk on very large threads because the chat tab now
prefetches multiple earlier pages on mount; the cap is intentionally
limited to 150 comments to bound that work.
- Low API risk because the server fix only changes the cursor predicate
construction for anchor-based comment pagination, but any mistake there
would affect older-comment paging order.

> I checked `ROADMAP.md` before opening this PR and this bug fix does
not duplicate planned core work.

## Model Used

- OpenAI Codex coding agent in the Paperclip local adapter environment.
The exact backend model ID and context window were not exposed
in-session. Tool-assisted workflow included shell execution, git/GitHub
CLI, local test execution, and targeted code edits.

## 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
- [ ] 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

server/src/services/issues.ts

@@ -1,5 +1,5 @@
 import { Buffer } from "node:buffer";
-import { and, asc, desc, eq, inArray, isNull, ne, or, sql } from "drizzle-orm";
+import { and, asc, desc, eq, gt, inArray, isNull, lt, ne, or, sql } from "drizzle-orm";
 import type { Db } from "@paperclipai/db";
 import {
   activityLog,
@@ -3138,14 +3138,14 @@ export function issueService(db: Db) {
         if (!anchor) return [];
         conditions.push(
           order === "asc"
-            ? sql<boolean>`(
-                ${issueComments.createdAt} > ${anchor.createdAt}
-                OR (${issueComments.createdAt} = ${anchor.createdAt} AND ${issueComments.id} > ${anchor.id})
-              )`
-            : sql<boolean>`(
-                ${issueComments.createdAt} < ${anchor.createdAt}
-                OR (${issueComments.createdAt} = ${anchor.createdAt} AND ${issueComments.id} < ${anchor.id})
-              )`,
+            ? or(
+                gt(issueComments.createdAt, anchor.createdAt),
+                and(eq(issueComments.createdAt, anchor.createdAt), gt(issueComments.id, anchor.id)),
+              )!
+            : or(
+                lt(issueComments.createdAt, anchor.createdAt),
+                and(eq(issueComments.createdAt, anchor.createdAt), lt(issueComments.id, anchor.id)),
+              )!,
         );
       }