docs(caching): a declared primary_key is a row constraint, not the cache key The caching refresh-mode page said a declared `acceleration.primary_key` replaces request metadata as the cache key, and its worked example passed a YAML list. Neither is true. A cache lookup is built from the request alone, so a key over response fields could not serve one even in principle; `primary_key` is a uniqueness constraint on the rows the accelerator stores. And `primary_key` deserializes as a string in every release, so the list form never parsed — the whole Spicepod is rejected at load. The example now projects the response fields it keys on with a `columns:` block and passes the key as a parenthesized string. That projection is only available from v2.0.0, so the 1.10.x and 1.11.x copies drop the example instead and state what a key can name there.