Scraper Breakage Detection Harness

You are a test-automation engineer building resilient validation systems for web scrapers.

Generate a test harness that detects when a scraper has silently broken due to target-site markup changes. The harness must run after every scrape and compare results against a stored baseline from the previous successful run.

**Scraper context:**
{{scraper-details}}

**Test assertions (implement all three):**
1. **Record count** – flag if the new run returns fewer than {{min-record-threshold}}% of the baseline count (excluding known-empty scenarios).
2. **Required-field fill rate** – for each required field, calculate the percentage of non-null, non-empty records. Alert if any field's fill rate drops below {{min-fill-rate}}% compared to baseline.
3. **Value shape** – verify data types, string-length ranges, regex patterns, and enum membership for key fields. Do not assert exact content; assert structure (e.g. emails match `^[^@]+@[^@]+$`, prices are positive numbers, dates parse correctly).

**Behavior:**
- Store each successful run's metrics (count, per-field fill rates, shape-validation pass rates) as the new baseline in a JSON file or database row.
- On failure, print a **loud, actionable report**: which assertion failed, baseline vs. current values, timestamp, and affected fields.
- Exit with a non-zero code so CI/CD pipelines catch the failure.

**Deliverables:**
1. Complete test-harness code with inline comments explaining each assertion and threshold check.
2. A **runbook** (≈150 words) that walks the operator through diagnosing the root cause:
   - **Layout change** (selectors broken) – symptoms, how to confirm, fix steps.
   - **Anti-bot block** (CAPTCHA, rate limit, IP ban) – detection signals, mitigation.
   - **Legitimately empty results** (site has no data today) – how to distinguish from breakage, when to update baseline.

Use clear variable names, modular functions for each assertion type, and include example threshold values as defaults. Write for Python unless the scraper-details specify another language.