## 1. Agree period, currency and conversion definitions

Restate period, CNY units, CVR denominator and conversion threshold from source-data.json. List missing baseline/attribution information. Do not connect Ads or change budgets. Save metric-contract.md.

Expected: A metric contract.
Check: Use yuan without dividing by a million; label the CVR convention.

## 2. Validate inputs and calculability

Check spend, impressions, clicks, conversions and value for each campaign. List numerator, denominator and calculation status for every metric. Do not fill missing values with zero or propose scale/stop actions.

Expected: An input-quality table.
Check: Zero denominators in AD02/AD03 are explicit.

## 3. Calculate ratios with reasons for nulls

Compute all four ratios with formulas. Return null plus reason when the denominator is zero. AD02 ROAS is 0, CPA is null. Compare prior CPA for AD01 only; do not fill other baselines.

Expected: Three reference metric rows.
Check: AD01: 2%, 10%, 20, 2.5; no Infinity, NaN or false zero CPA.

## 4. Write observations before investigation ideas

Write scope, metrics, comparable baselines, small-sample flags, missing information and human investigation suggestions. Give no scale/stop decision for AD02/03. State evidence and limits for every suggestion; do not assert causes.

Expected: A report and investigation list.
Check: Spend changes are not directly called performance changes; sample flags remain visible.

## 5. Read a small live report and verify source fields

Read only <account/period/grouping>, at most 5 groups. Record fields/units, conversion action, time zone and attribution window. Recalculate one group from source values. Deliver files only; change no ads and send no Slack messages.

Expected: A traceable live comparison or blocker.
Check: No bid/budget action; account, window and units can be verified.

## 6. Version backfills and definition changes

Draft an ads-scoreboard Skill with field/formula versions, period/attribution, zero denominators, small samples, backfill revisions and read-only scope. Propose a private-report Routine only. Review budgets and external delivery separately.

Expected: A report and revision standard.
Check: Historical and revised definitions remain distinguishable.