semantic-layer-change-reviewlisted

## Purpose Changes to the semantic layer directly impact dashboards and business reporting. A silent drift in a metric definition destroys trust. Review every semantic-layer change for mathematical soundness and backwards compatibility before approval. ## When to Use - A PR modifies metric or semantic model YAML - A metric's `expr`, aggregation, or filters are changing - New dimensions or entities are being added to an existing semantic model ## Inputs - The semantic-layer diff (semantic models, metrics, saved queries) - The underlying model's grain and entity keys ## Workflow 1. **Enumerate what changed:** ```bash git diff origin/main...HEAD -- '*.yml' '*.yaml' dbt ls --resource-type metric dbt ls --resource-type semantic_model ``` 2. **Identify the change type:** - **Addition** — safe (adding a new metric or dimension). - **Deprecation** — requires communication (removing a metric). - **Modification** — high risk (changing the SQL expression, aggregation, or filters of an existing metric). 3. **Evaluate mathematical soundness:** - Are we averaging an average? - Are we summing a distinct count? - Does adding this dimension cause a fan-out that inflates the metric? 4. **Check backwards compatibility.** If an existing metric's logic is changed, you MUST flag it. The recommended path is dbt's metric versioning or a new metric (e.g., `revenue_v2`) rather than silently altering historical numbers. Find consumers of the metric before jud