fix(codegen): lineage table CHECK refuses self-references#78
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Closes #42. `verisimdb_lineage_graph` had no constraint preventing `(source_entity, source_table) == (target_entity, target_table)`. Any row inserted with matching source/target tuples is a self-loop and falsifies the README's "DAG" framing at the structural level. Add a CHECK constraint: CHECK (source_entity <> target_entity OR source_table <> target_table) i.e. at least one component of the (entity, table) pair must differ. Two entities with the same id across different tables (a legitimate cross-table derivation) still pass. Multi-hop cycle prevention is a runtime concern (any number of CHECKs can't catch chains); kept as a separate follow-up (V-L2-I2). Test `test_lineage_table_has_self_reference_check` asserts the exact CHECK clause appears in the emitted DDL with lineage enabled. `cargo clippy --all-targets -- -D warnings` clean; 35 unit tests pass. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Summary
Per V-L2-I1: lineage edges accepted
source == target, so the README's DAG claim was unenforced at the structural level. Add CHECK:Multi-hop cycle prevention is a runtime concern (tracked as the V-L2-I2 follow-up).
Closes
Test plan
cargo clippy --all-targets -- -D warningscleancargo test --lib --bins35/35 (1 new:test_lineage_table_has_self_reference_check)