[kvlonge]

Why

First milestone of the Rust-hosted compile (CHI-589): move discovery logic out of Python. Each port deletes the Python it replaces and keeps behaviour identical, including error text, exception classes and which error is reported first.

Changes

• Model files are native records (sqlbuild._native.DiscoveredSqlModelFile) built directly by native discovery; the model loop reads them without Python unpacking. Records still copy, pickle and support lint-fix edits.
• Cross-file discovery validation (identities, name conflicts, Python node dependencies and cycles, seed CSV headers, path defaults) runs in sqlbuild-discovery::project_validation. The seed header reader matches Python's csv reader; the running interpreter still judges CSV dialect settings, so 3.13/3.14 errors are unchanged.
• Source and seed YAML declarations, including freshness, ingestr and dlt sources, are parsed in sqlbuild-discovery::yaml_entries.
• Python-exact strip, casefold, isalnum, isdigit and isspace helpers in sqlbuild-core.
• About 2,500 lines of Python deleted; the boundary baseline drops from 146,314 to 143,789.

Verification

• Compiler differential: all 368 projects match their goldens, with full discovery and render coverage.
• Identical compile output to main on a generated 1k-model project and a private project (cold and edit).
• Existing source/schema YAML unit tests run unchanged through the native parsers; new integration tests pass identically against main.
• New Rust tests, including 127 CSV header reads recorded from CPython.
• make test, make check-ci, one review plus a follow-up pass.
• 10k benchmark: cold compile about 1.5% faster, edit compile unchanged.