feat(devops): diagnose slow HK requests and dependency timings

docs/operations/cms-error-center.md

@@ -63,3 +63,23 @@ Obsolete global overrides were removed; a scoped esbuild override remains becaus
 Drizzle Kit's loader still resolves a vulnerable legacy development-server build.
 The two deprecated esbuild-kit packages remain upstream dependencies of Drizzle
 Kit; replacing the ORM is not warranted for this tooling issue.
+
+## HK request performance
+
+Open **DevOps → Request performance** (`/admin/devops/performance`). Access requires `DEVOPS_VIEW`; collection only retains requests that passed authentication and permission checks through `withAdmin`.
+
+The view shows recent requests, their server duration, completed database query count/time/errors, monitored curl download count/time/errors, HTTP status and the existing operation ID. Search by route or operation ID, sort by duration or recency, and filter requests taking at least one second.
+
+### Measurement boundaries
+
+- Duration ends when the handler returns its response. Streaming completion, background jobs, browser rendering and public pages are not measured.
+- Database spans wrap the shared mysql2 promise pool and transaction connection query/execute calls. Query parameters and SQL are never collected. Explicit transaction connection acquisition and transaction control methods are not separate spans.
+- External spans currently cover `curlFetchText` and `curlDownload`; ordinary fetch calls and other integrations are not covered.
+- Concurrent dependency durations can exceed wall-clock request duration. Do not subtract the sums to infer application CPU time.
+- Dynamic route values and query strings are removed. No request bodies, headers, usernames, download URLs or SQL text are stored.
+
+### Storage and operation
+
+No new environment variables or packages are required. Redis stores at most 200 recent samples under `cms:performance:v1`, with one-hour retention. Writes are best effort, restricted to an already-ready connection and at most four pending batches; the request never waits for persistence. The view reads at most 200 entries and falls back after one second if shared storage is unavailable.
+
+An in-process buffer preserves up to 200 samples during outages. The page explicitly labels this local mode; it is per instance and disappears on restart. Filtering applies to the retained samples, not complete traffic history. Under load or during storage outages, some shared samples may be omitted.