## Problem
Every `GET /api/experimental/chats/{chatID}` call was blocking for
200-800ms because the `getChat` handler called `resolveChatDiffStatus`,
which unconditionally hit the git provider API (e.g. GitHub's `GET
/repos/{owner}/{repo}/pulls?head=...`) via `ResolveBranchPullRequest` —
even when the cached diff status was fresh.
This made every chat page load at `/agents/{id}` noticeably slow.
## Root cause
The call chain was:
1. `getChat` → `resolveChatDiffStatus`
2. `resolveChatDiffStatus` → `resolveChatDiffReference` →
`gp.ResolveBranchPullRequest(...)` **(external HTTP call)**
3. Only **after** the external call: `chatDiffStatusIsStale(status,
now)` check
The staleness check happened after the expensive work, so every request
paid the cost regardless of cache freshness.
## Fix
`getChat` now returns the cached `chat_diff_statuses` row directly from
the database. The background `gitsync` worker already keeps these rows
fresh (every `DiffStatusTTL = 120s`), so inline resolution was
redundant.
The `resolveChatDiffContents` endpoint (which fetches actual diff
content) still uses the full resolution path since it needs to make
provider API calls by design.
## Changes
- `getChat` reads cached diff status from DB instead of calling
`resolveChatDiffStatus`
- Remove `resolveChatDiffStatus` (dead code — no production callers)
- Remove `chatDiffStatusIsStale` and `chatDiffStatusTTL` (dead code)
- Remove `RefreshesStaleStatusWithExternalAuth` test (tested the removed
inline refresh path)
<details><summary>Decision log</summary>
- **Why not just add a staleness gate?** The background worker already
handles refreshes on the same schedule. Adding an early-return-if-fresh
would work but leaves dead code for the stale path that's never
exercised in production (the worker gets there first). Removing the
inline path entirely is simpler and eliminates the external API
dependency from the read path.
- **Why keep `resolveChatDiffContents` unchanged?** That endpoint's job
is to fetch the actual diff content from the provider, so external API
calls are inherent to its purpose.
</details>
Kyle Carberry
7861fcf1f6