Detect Prod Regressions

Run this skill as an evidence-first production sweep. The deliverable is a set of measured candidate bugs summarized for a human reviewer in a compact table, plus a short summary of what was checked. Do not touch Linear automatically.

Required Scope

Always review all production environments unless the user explicitly narrows the scope:

• prod-us
• prod-eu
• prod-hipaa
• prod-jp

Query both Datadog sites when needed. Default to the EU site for prod-eu and the US site for the other production envs, but verify by querying facets or running a small count query rather than assuming where a tag lives.

Measurement Rules

• Ground every bug claim in a measurable signal: counts, rates, p50/p95/p99 duration, trace samples, flamegraphs, monitor thresholds, or benchmark comparisons.
• If a requested measurement is missing or unavailable, write exactly "No measurements found" for that signal.
• Treat a bug as new only when a recent window shows a new or materially worse error cluster or latency regression versus a baseline.
• Do not rely only on top-volume clusters. Also inspect new low-occurrence errors that look like coding bugs or edge cases, such as invariant failures, unexpected null/undefined values, validation surprises, unhandled promise rejections, serialization failures, impossible enum states, or one-off 500s on uncommon routes.
• For latency, error-rate, throughput, saturation, or performance findings, focus on how the signal worsened over time: recent versus preceding window, recent versus same window 7 days earlier, and post-change versus pre-change when deployment markers are available.
• Prefer high-level aggregations before individual events; drill into example logs, spans, traces, or flamegraphs only after a cluster is identified.
• Do not infer customer impact, root cause, or severity beyond what the measurements support.

Baseline Window

Use the user's stated window when provided. Otherwise:

1. Compare the most recent 24 hours with the preceding 24 hours.
2. Add a same-day or same-hour historical baseline, usually the matching window 7 days earlier, when Datadog data is available.
3. If release or deployment markers, service versions, git SHAs, or change timestamps are visible, compare post-change versus pre-change windows.

Include the recent window and baseline window in any later handoff to linear-bug-triage after the human explicitly approves sharing findings in Linear.

Datadog Sweep

Before querying Datadog, load the relevant Datadog MCP guidance for logs, traces, metrics, and visualizations. Use the existing datadog-query-recipes skill for query syntax, production environment coverage, tenant/public API usage, and queue consumer measurements. Use debug-issue-with-datadog when a candidate regression becomes an incident-style root-cause analysis.

For each environment, check:

1. Datadog errors

   • Use Datadog Error Tracking to review error groups, new issues, regressions, affected services, and occurrence timelines. Also check the EU Datadog site equivalent when environment data is stored there.
   • Aggregate error counts and rates by env, service, route/resource, status code, error.type, and error.message.
   • Compare recent counts/rates to the baseline.
   • Include low-occurrence new error groups when the stack, message, route, or affected code path suggests a coding bug or edge case, even if occurrence counts are too small for top-N dashboards.

2. Datadog error logs

   • Aggregate status:error logs by service, route/resource, source, error.message, tenant/project identifiers when present, and environment.
   • Open representative logs only for clusters with measurable increase.

3. Datadog error spans

   • Aggregate error spans by env, service, resource_name, http.route, error.type, and error.message.
   • Fetch representative traces only after grouping identifies a candidate regression.

4. API route latencies

   • Focus on service:web HTTP spans and metrics such as trace.http_request.duration when available.
   • Compare p50, p95, and p99 by route/resource and environment.
   • Rank candidates by worsening over time, not only by absolute latency: recent versus baseline deltas, slope, and newly introduced tail latency.
   • Use trace samples or flamegraphs for routes whose latency materially regressed.

Keep Datadog links for every query, trace, dashboard, or flamegraph used as evidence.

Linear Handoff

Before doing anything in Linear, show the human reviewer a findings table in chat and ask for permission to share the findings in Linear. The table should include one row per candidate with:

• Candidate / cluster name.
• Environments.
• Service and route/resource.
• Recent window measurement.
• Baseline measurement.
• Delta / regression summary.
• Key evidence links.
• Recommended Linear action (comment existing, create new, or none).

Use a concrete markdown table shaped like this:

| Candidate | Envs | Service / Route | Recent Window | Baseline | Delta | Evidence | Proposed Linear Action |
| --- | --- | --- | --- | --- | --- | --- | --- |
| Public scores latency regression | prod-us | `web` `GET /api/public/v2/scores/index` | p95 `7.44s`, p99 `12.77s`, count `71,448` | p95 `4.34s`, p99 `6.60s`, count `26,024` | p95 `+72%`, p99 `+94%`, volume `+174%` | [metrics](https://app.datadoghq.com/) [spans](https://app.datadoghq.com/) [trace](https://app.datadoghq.com/) | comment existing |
| ClickHouse socket hang up cluster | prod-us | `web-iso` `POST /` | errors `14,088` | errors `6,026` | `+134%` errors | [spans](https://app.datadoghq.com/) [trace](https://app.datadoghq.com/) | comment existing |
| Ingestion DLQ monitor noise | prod-eu | `worker-cpu` `langfuse.queue.ingestion.dlq_length` | max `150` | max `150` | flat | [metrics](https://app.datadoghq.eu/) | none |

If a requested signal is unavailable, write No measurements found in the relevant cell instead of leaving it blank.

Only if the human explicitly approves, use linear-bug-triage for Linear search, deduplication, evidence comments, Triage issue creation, labels, and ticket formatting. Treat that skill as the source of truth for Linear behavior once approval is granted.

Hand off:

• Recent window and baseline window.
• Measured deltas or No measurements found for unavailable signals.
• Affected environments, services, routes/resources, status codes, and top error messages.
• Datadog links for every query, trace, dashboard, metric graph, or flamegraph used as evidence.

Final Response

Summarize:

• The windows compared and all prod environments checked.
• The findings table shown to the human.
• Whether the human approved sharing findings in Linear.
• New Linear issues created, with links, only if approval was granted.
• Existing Linear issues commented on, with links, only if approval was granted.
• Candidate signals skipped with "No measurements found".
• A compact "no new bugs found" statement when no issue-worthy regressions were measured.