prd-v08-drift-baseline-compare

# Drift: Baseline / Compare / History

Position in workflow: v0.8 Monitoring Setup → **v0.8 Drift: Baseline / Compare / History** → v0.8 Runbook Creation

## Execution Mode

Default is **standard**. See [`.claude/rules/08-skill-execution-modes.md`](../../rules/08-skill-execution-modes.md) for selection logic.

| Mode | What this skill produces |
|------|--------------------------|
| **quick** | One metric / config / dataset baselined; weekly compare schedule; simple threshold alert |
| **standard** | 3–5 things monitored; baseline + tiered thresholds (warn / critical); compare cadence; history retention |
| **deep** | Full portfolio; multi-dimensional comparison (per segment, per environment); regression-cause matrix; auto-baselining after intentional change |

## What This Does

Generalizes a pattern AgriciDaniel's `claude-seo` skill encodes for SEO drift — **baseline → snapshot → compare → history** — into a reusable monitoring shape that works for any metric, config, or dataset that can change over time and needs to be watched.

This is **drift monitoring**, distinct from alerting on absolute thresholds. Alerting answers "is X over the line right now?" Drift monitoring answers "is X different from last week's normal?" — which catches slow regressions that absolute thresholds miss.

Examples of things worth drift-monitoring:
- **KPI**: activation rate week-over-week
- **AI search position**: ChatGPT/Perplexity ranking for target queries
- **Config**: feature-flag rollout percentages
- **Performance**: p95 latency by endpoint
- **Cost**: per-user infra cost
- **Marketing**: per-channel CAC trend
- **Content**: changelog post engagement
- **Third-party**: vendor pricing pages (price hikes), competitor feature pages (parity loss)

## How It Works

1. **Pick what to monitor** — One thing per MON-DRIFT- entry. Must be:
   - Quantifiable (number, percentage, list, configuration value)
   - Snapshotable (captureable at a point in time, ideally automatically)
   - Causally interpretable (when it changes, you know enough to investigate)
2. **Capture the baseline** — Take a snapshot. Date it. Store in version control or a known location (`status/baselines/`, `monitoring/snapshots/`, etc.).
3. **Define drift thresholds**:
   - **Warn**: meaningful change (e.g., 10% drift in a KPI; any change in a config value)
   - **Critical**: serious change (e.g., 25% KPI drop; breaking config change)
   - **Recalibrate**: intentional change that should refresh the baseline (e.g., after a feature rollout, the baseline is wrong; refresh it)
4. **Set compare cadence** — How often does this get re-snapshotted?
   - Hot (hourly/daily): production KPIs, AI search positions during a launch
   - Warm (weekly): standard product KPIs, content engagement
   - Cool (monthly): vendor pricing, competitor feature parity, infra cost
5. **Build the compare procedure** — A script or runbook that:
   - Takes a new snapshot
   - Diffs against baseline
   - Computes drift % per dimension
   - Emits warn/critical signals at thresholds
   - Appends to history log
6. **Plan auto-baselining after intentional change** [standard+] — When the team makes a deliberate change (ships a feature that should improve activation), the old baseline becomes wrong. Define what triggers a baseline refresh and who approves it.

## Example

Monitoring AI search position for the target query "best CRO tool for SaaS founders" across 3 surfaces. (Generalized from AEO Audit re-test cadence.)

**Baseline** (2026-04-01):
```
ChatGPT: not mentioned (rank: --)
Perplexity: rank 4 of 5, miscategorized as "analytics"
AI Overviews: not mentioned
Sources cited: [competitor1.com, competitor2.com, reddit.com/r/SaaS]
```

**Thresholds**:
- Warn: rank changes by ≥1, sources list changes, miscategorization persists
- Critical: dropped from any surface where previously mentioned

**Compare cadence**: weekly during launch month, monthly after.

**Re-snapshot** (2026-04-15):
```
ChatGPT: rank 3 of 5 (NEW)         ← improved
Perplexity: rank 3 of 5, category corrected (NEW)   ← improved
AI Overviews: rank 5 of 7 (NEW)    ← improved
Sources cited: [+ ourdomain.com (NEW), ...]
```

**Compare output**: 3 surfaces improved. Likely cause: alternatives-pages campaign + new CRO-anchored blog post indexed.

**History append**: 2026-04-01 → 2026-04-15 row added to history log.

**Action**: No alert; positive drift. Baseline can stay (next compare in 2 weeks). If the trend reverses, the baseline catches it.

## What You Get Back

- **MON-DRIFT-\* entries** (one per monitored thing) — Baseline snapshot, thresholds, cadence, compare procedure, history pointer
- **History logs** in `status/drift-history/<id>.jsonl` (or similar) — Append-only record of compare results
- **Compare scripts** (`scripts/drift/<id>.sh` or equivalent) when automatable

## When to Use It

| Trigger | Mode |
|---------|------|
| Post-launch — need ongoing watch on KPIs | standard |
| AEO Audit results to maintain | standard |
| Competitor feature parity tracking | standard |
| Vendor / third-party pricing watch | quick |
| Performance regression hunting | deep |
| Infrastructure cost trend | quick |

Do not use for things that are already covered by **threshold-based alerting** (RED/USE metrics, MON-* alerts). Drift is for trends; alerting is for absolutes.

## Consumes

- **MON-\* monitoring infrastructure** (from v0.8 Monitoring Setup) — Data sources for KPI/performance drift; existing dashboards
- **KPI-\* metric definitions** (from v0.3 + v0.9) — What's worth watching
- **CFD-\* competitor research** (from v0.2 + ongoing) — For competitor-parity drift
- **GTM-AEO-\* Coverage Matrix** (from v0.9 AEO Audit) — For AI search position drift
- **BR-PRICING-\*** (from v0.3 + v0.9 Offer) — For pricing drift on our side; vendor-pricing drift watches their side
- **DEP-\* release entries** — Intentional changes that may trigger baseline refresh

## Produces

- **MON-DRIFT-\* entries** with `Type=Drift-Baseline` — On