[codex] Improve issue detail and issue-list UX (#3678)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - A core part of that is the operator experience around reading issue
state, agent chat, and sub-task structure
> - The current branch had a long run of issue-detail and issue-list UX
fixes that all improve how humans follow and steer active work
> - Those changes mostly live in the UI/chat surface and should be
reviewed together instead of mixed with workspace/runtime work
> - This pull request packages the issue-detail, chat, markdown, and
sub-issue list improvements into one standalone change
> - The benefit is a cleaner, less jumpy, more reliable issue workflow
on desktop and mobile without coupling it to unrelated server/runtime
refactors

## What Changed

- Stabilized issue chat runtime wiring, optimistic comment handling,
queued-comment cancellation, and composer anchoring during live updates
- Fixed several issue-detail rendering and navigation regressions
including placeholder bleed, local polling scope, mobile inbox-to-issue
transitions, and visible refresh resets
- Improved markdown and rich-content handling with advisory image
normalization, editor fallback behavior, touch mention recovery, and
`issue:` quicklook links
- Refined sub-issue behavior with parent-derived defaults, current-user
inheritance fixes, empty-state cleanup, and a reusable issue-list
presentation for sub-issues
- Added targeted UI tests for the new issue-detail, chat scroll/message,
placeholder-data, markdown, and issue-list behaviors

## Verification

- `pnpm vitest run ui/src/components/IssueChatThread.test.tsx
ui/src/components/MarkdownEditor.test.tsx
ui/src/components/IssuesList.test.tsx
ui/src/context/LiveUpdatesProvider.test.tsx
ui/src/lib/issue-chat-messages.test.ts
ui/src/lib/issue-chat-scroll.test.ts
ui/src/lib/issue-detail-subissues.test.ts
ui/src/lib/query-placeholder-data.test.tsx
ui/src/hooks/usePaperclipIssueRuntime.test.tsx`

## Risks

- Medium: this branch touches the highest-traffic issue-detail UI paths,
so regressions would show up as chat/thread or sub-issue UX glitches
- The changes are UI-heavy and would benefit from reviewer screenshots
or a quick manual browser pass before merge

## Model Used

- OpenAI Codex coding agent (GPT-5-class runtime in Codex CLI; exact
deployed model ID is not exposed in this environment), reasoning
enabled, tool use and local code execution enabled

## 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 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

---------

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

ui/src/context/LiveUpdatesProvider.tsx

@@ -1,12 +1,14 @@
 import { useEffect, useRef, type ReactNode } from "react";
-import { useQuery, useQueryClient, type QueryClient } from "@tanstack/react-query";
-import type { Agent, Issue, LiveEvent } from "@paperclipai/shared";
+import { useQuery, useQueryClient, type InfiniteData, type QueryClient } from "@tanstack/react-query";
+import type { Agent, Issue, IssueComment, LiveEvent } from "@paperclipai/shared";
 import type { RunForIssue } from "../api/activity";
 import type { ActiveRunForIssue, LiveRunForIssue } from "../api/heartbeats";
+import { issuesApi } from "../api/issues";
 import { authApi } from "../api/auth";
 import { useCompany } from "./CompanyContext";
 import type { ToastInput } from "./ToastContext";
 import { useToast } from "./ToastContext";
+import { upsertIssueCommentInPages } from "../lib/optimistic-issue-comments";
 import { queryKeys } from "../lib/queryKeys";
 import { toCompanyRelativePath } from "../lib/company-routes";
 import { useLocation } from "../lib/router";
@@ -83,6 +85,7 @@ interface VisibleRouteOptions {
 }
 
 interface VisibleIssueRouteContext {
+  routeIssueRef: string;
   issueRefs: Set<string>;
   assigneeAgentId: string | null;
   runIds: Set<string>;
@@ -189,6 +192,7 @@ function resolveVisibleIssueRouteContext(
   }
 
   return {
+    routeIssueRef: issueRef,
     issueRefs,
     assigneeAgentId: issue?.assigneeAgentId ?? null,
     runIds,
@@ -254,6 +258,95 @@ function shouldSuppressAgentStatusToastForVisibleIssue(
   return !!agentId && agentId === context.assigneeAgentId;
 }
 
+function shouldDeferIssueRefetchForVisibleAgentActivity(
+  queryClient: QueryClient,
+  pathname: string,
+  payload: Record<string, unknown>,
+  options?: VisibleRouteOptions,
+): boolean {
+  const entityType = readString(payload.entityType);
+  const entityId = readString(payload.entityId);
+  const actorType = readString(payload.actorType);
+  const action = readString(payload.action);
+  const details = readRecord(payload.details);
+
+  if (entityType !== "issue" || !entityId) return false;
+  if (actorType !== "agent" && actorType !== "system") return false;
+  if (action !== "issue.updated") return false;
+  if (readString(details?.source) === "comment") return false;
+
+  const context = resolveVisibleIssueRouteContext(queryClient, pathname, options);
+  if (!context) return false;
+
+  return overlaps(context.issueRefs, buildIssueRefsForPayload(entityId, details));
+}
+
+function shouldDeferVisibleIssueCommentActivity(
+  queryClient: QueryClient,
+  pathname: string,
+  payload: Record<string, unknown>,
+  options?: VisibleRouteOptions,
+): boolean {
+  const entityType = readString(payload.entityType);
+  const entityId = readString(payload.entityId);
+  const action = readString(payload.action);
+  const details = readRecord(payload.details);
+
+  if (entityType !== "issue" || !entityId) return false;
+  if (action !== "issue.comment_added") return false;
+
+  const context = resolveVisibleIssueRouteContext(queryClient, pathname, options);
+  if (!context) return false;
+
+  return overlaps(context.issueRefs, buildIssueRefsForPayload(entityId, details));
+}
+
+async function hydrateVisibleIssueComment(
+  queryClient: QueryClient,
+  pathname: string,
+  payload: Record<string, unknown>,
+  options?: VisibleRouteOptions,
+) {
+  const entityType = readString(payload.entityType);
+  const action = readString(payload.action);
+  const details = readRecord(payload.details);
+  const commentId = readString(details?.commentId);
+
+  if (entityType !== "issue" || action !== "issue.comment_added" || !commentId) return false;
+
+  const context = resolveVisibleIssueRouteContext(queryClient, pathname, options);
+  if (!context) return false;
+
+  const entityId = readString(payload.entityId);
+  if (!entityId || !overlaps(context.issueRefs, buildIssueRefsForPayload(entityId, details))) {
+    return false;
+  }
+
+  try {
+    const comment = await issuesApi.getComment(context.routeIssueRef, commentId);
+    queryClient.setQueryData<InfiniteData<IssueComment[], string | null> | undefined>(
+      queryKeys.issues.comments(context.routeIssueRef),
+      (current) => {
+        if (!current) {
+          return {
+            pages: [[comment]],
+            pageParams: [null],
+          };
+        }
+
+        return {
+          ...current,
+          pages: upsertIssueCommentInPages(current.pages, comment),
+        };
+      },
+    );
+    return true;
+  } catch {
+    queryClient.invalidateQueries({ queryKey: queryKeys.issues.comments(context.routeIssueRef) });
+    return false;
+  }
+}
+
 const ISSUE_TOAST_ACTIONS = new Set(["issue.created", "issue.updated", "issue.comment_added"]);
 const AGENT_TOAST_STATUSES = new Set(["error"]);
 const RUN_TOAST_STATUSES = new Set(["failed", "timed_out", "cancelled"]);
@@ -481,6 +574,7 @@ function invalidateActivityQueries(
   companyId: string,
   payload: Record<string, unknown>,
   currentActor: { userId: string | null; agentId: string | null },
+  options?: { pathname?: string; isForegrounded?: boolean },
 ) {
   queryClient.invalidateQueries({ queryKey: queryKeys.activity(companyId) });
   queryClient.invalidateQueries({ queryKey: queryKeys.dashboard(companyId) });
@@ -504,9 +598,28 @@ function invalidateActivityQueries(
           (action === "issue.updated" && readString(details?.source) === "comment")) &&
         ((actorType === "user" && !!currentActor.userId && actorId === currentActor.userId) ||
           (actorType === "agent" && !!currentActor.agentId && actorId === currentActor.agentId));
+      const visibleIssueAgentActivity =
+        !!options?.pathname &&
+        shouldDeferIssueRefetchForVisibleAgentActivity(
+          queryClient,
+          options.pathname,
+          payload,
+          { isForegrounded: options.isForegrounded },
+        );
+      const visibleIssueCommentActivity =
+        !!options?.pathname &&
+        shouldDeferVisibleIssueCommentActivity(
+          queryClient,
+          options.pathname,
+          payload,
+          { isForegrounded: options.isForegrounded },
+        );
       const issueRefs = resolveIssueQueryRefs(queryClient, companyId, entityId, details);
       for (const ref of issueRefs) {
-        const invalidationOptions = selfCommentActivity ? { refetchType: "inactive" as const } : undefined;
+        const invalidationOptions =
+          (selfCommentActivity || visibleIssueAgentActivity || visibleIssueCommentActivity)
+            ? { refetchType: "inactive" as const }
+            : undefined;
         queryClient.invalidateQueries({ queryKey: queryKeys.issues.detail(ref), ...invalidationOptions });
         queryClient.invalidateQueries({ queryKey: queryKeys.issues.activity(ref), ...invalidationOptions });
         if (action === "issue.comment_added") {
@@ -655,7 +768,10 @@ function handleLiveEvent(
   }
 
   if (event.type === "activity.logged") {
-    invalidateActivityQueries(queryClient, expectedCompanyId, payload, currentActor);
+    invalidateActivityQueries(queryClient, expectedCompanyId, payload, currentActor, { pathname });
+    if (shouldDeferVisibleIssueCommentActivity(queryClient, pathname, payload)) {
+      void hydrateVisibleIssueComment(queryClient, pathname, payload);
+    }
     const action = readString(payload.action);
     const toast =
       buildActivityToast(queryClient, expectedCompanyId, payload, currentActor) ??
@@ -712,8 +828,11 @@ export const __liveUpdatesTestUtils = {
   buildAgentStatusToast,
   buildRunStatusToast,
   closeSocketQuietly,
+  hydrateVisibleIssueComment,
   invalidateActivityQueries,
   resolveLiveCompanyId,
+  shouldDeferIssueRefetchForVisibleAgentActivity,
+  shouldDeferVisibleIssueCommentActivity,
   shouldSuppressActivityToastForVisibleIssue,
   shouldSuppressRunStatusToastForVisibleIssue,
   shouldSuppressAgentStatusToastForVisibleIssue,