fix(documents): say whether an exact revision read is still current (#19939)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work
> - Task documents keep a revision history, and agents read and restore
revisions through the API
> - The exact-revision read returns one revision, but it does not say if
that revision is still current
> - An agent read the revision that it restored earlier by its ID and
reported it as "latest", but another person had saved a newer edit
> - This pull request adds the document's current revision to the
exact-revision read
> - The benefit is that a pinned read cannot pass as a read of the
current document

## Linked Issues or Issue Description

**What happened**

In a chat eval, the agent restored a plan revision. Then another person
saved a new revision. The user asked the agent to read the current plan.
The agent called `GET
/api/issues/{id}/documents/plan/revisions/{revisionId}` with the ID of
its own restored revision. The response did not show that a newer
revision existed. The agent reported the old revision as the latest and
said that the read confirmed this.

**Expected behavior**

A read of one exact revision must show if that revision is still
current, and which revision is current. Then the reader can see a newer
edit and read the current document.

**Steps to reproduce**

1. Save two revisions of a task plan.
2. Call `GET
/api/issues/{id}/documents/plan/revisions/{firstRevisionId}`.
3. See that the response gives no sign that revision 2 is the current
revision.

## What Changed

- `getIssueDocumentRevision` now also returns `latestRevisionId`,
`latestRevisionNumber` and `isLatest`.
- Shared type `ExactDocumentRevision` describes this response. The UI
client uses it.
- The OpenAPI description of the exact-revision read names these fields
and points to `GET /api/issues/{id}/documents/{key}` for the current
text.
- The service test checks `isLatest` for an older and a current
revision.

## Verification

- `cd server && pnpm exec vitest run
src/__tests__/documents-service.test.ts
src/__tests__/openapi-routes.test.ts` (42 passed).
- `npx tsc --noEmit -p packages/shared` passes.

## Risks

- Low risk. The change only adds fields to a read response. No caller
removes or renames a field. No migration.

## Model Used

- Anthropic Claude Opus 5.5 (`claude-opus-5-5`), with tool use and code
execution.

## 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
- [ ] All Paperclip CI gates are green
- [ ] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

ui/src/api/issues.ts

@@ -11,6 +11,7 @@ import type {
   InboxMineSnapshot,
   CreateIssueTreeHold,
   DocumentRevision,
+  ExactDocumentRevision,
   FeedbackTargetType,
   FeedbackTrace,
   FeedbackVote,
@@ -747,7 +748,7 @@ export const issuesApi = {
       `/issues/${id}/documents/${encodeURIComponent(key)}/revisions`,
     ),
   getDocumentRevision: (id: string, key: string, revisionId: string) =>
-    api.get<DocumentRevision>(`/issues/${id}/documents/${encodeURIComponent(key)}/revisions/${encodeURIComponent(revisionId)}`),
+    api.get<ExactDocumentRevision>(`/issues/${id}/documents/${encodeURIComponent(key)}/revisions/${encodeURIComponent(revisionId)}`),
   restoreDocumentRevision: (id: string, key: string, revisionId: string) =>
     api.post<IssueDocument>(
       `/issues/${id}/documents/${encodeURIComponent(key)}/revisions/${revisionId}/restore`,