[kvlonge]

Why

Compile reports P013 when a mock the test uses reads a helper that calls a reference, because mocks are defined before the models a test runs and such a helper cannot resolve. That check only counted mocks a check reads by CTE name. A mock reached through a reference call, such as __source("item_returns") resolving to __source__item_returns, was missed, so the test compiled and then failed at run time with a missing table. The mock-only P013 also pointed at a source call when the message was about the model, and told users to "keep" a __ref() they had not written.

Changes

• Mocks reached through reference calls in expected rows, assertions and the helpers they read now count as used. These are the same reads that drive helper resolution. A used mock that reads a helper calling a reference, directly or through a middle helper, fails compile with a located P013.
• The mock-only P013 points at the mocked model's __ref( call when a check reads both a mocked source and a mocked model.
• When the check reads the mocked model by CTE name, such as FROM __ref__items, its help says to call __ref("items") instead of keep it.

Python-only change; no native code touched.

Verification

• DuckDB E2E on the python, native and native-preview engines: the reported repro, both directly and through a middle helper, plus both message cases. The new mock cases fail without the fix.
• The bundled example projects, the e2e fixture and a fresh playground still compile with no new errors
• Focused compile and attachment tests, make compiler-differential-shipped, tests/e2e/scripts/compiler_differential, make check-ci, hygiene scan