[kvlonge]

Why

M3g moves the compile attachments (everything that is not a model) onto the native path behind the native-preview engine, so the preview compile keeps closing the gap to an all-native compile. Output must stay byte-identical to Python or defer to it.

Changes

• New NativeStage.ATTACHMENTS (preview tier) and a sqlbuild-attachments crate.
• Authored SQL outside models (sources, functions, tests, scenarios, audits, hooks) uses the native static variable substitution and declaration reference scan. SQL with $ keeps Python interpolation so unclosed dollar quotes raise Python's message.
• Source and function header ${...} templates expand natively, recording the same environment reads. A native rejection Python accepts raises NativeStageMismatchError.
• Attached generic audits render natively: argument merge, raw and quoted @name rendering, severity and run scope. Conflicts, unknown values, odd argument types and non-ASCII whitespace defer to Python.
• Seed declarations pair with seed files natively.
• Cursor intrinsic rejection outside models runs natively; anything Python could reject defers.
• Macros in every attachment kind already run through the feat(native): batch and cache macro calls behind the preview engine #1013 bridge; a new project test proves it for audits, built-in audits, functions, sources, tests, scenarios and hooks.
• The differential corpus gains a templated source and function (source_template, function_header_template render kinds).

Verification

• cargo test --workspace, clippy and fmt (1.98.0)
• Seeded Python-vs-preview parity tests for authored SQL, audit rendering and cursor intrinsics, plus a whole-project compile-input test across engines
• make compiler-differential with stage captures and full coverage: 168/168; make compiler-differential-shipped: 162/162
• tests/e2e/scripts/compiler_differential: 18 passed
• make check-ci, make test (11701 passed), hygiene scan