fix(codegen): provenance view uses ROW_NUMBER for latest-per-entity (#82)

* fix(codegen): temporal current-version UNIQUE; valid_to CHECK

Closes #41.

`verisimdb_temporal_versions` had a non-unique partial index on
`(entity_id, table_name) WHERE valid_to IS NULL`. Two concurrent
writers could both successfully insert a row with `valid_to=NULL` for
the same entity, leaving two "current" versions and breaking the
point-in-time query semantics. There was also no constraint that
`valid_to` (when set) couldn't precede `valid_from`.

  - Promote the partial index to `CREATE UNIQUE INDEX` so the storage
    layer enforces "at most one current version per (entity, table)".
  - Add `CHECK (valid_to IS NULL OR valid_to >= valid_from)` so a
    version interval can't be backwards.

Test `test_temporal_table_has_unique_partial_index_and_valid_to_check`
asserts both clauses appear in the emitted DDL with temporal enabled.

`cargo clippy --all-targets -- -D warnings` clean; 37 unit tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* fix(codegen): provenance view uses ROW_NUMBER for latest-per-entity

Closes #40.

`generate_provenance_view` emitted a correlated MAX(timestamp) subquery
whose outer reference `verisimdb_provenance_log.entity_id` was
ambiguous: the same table appears in multiple nested scopes, and
depending on planner choices the correlation either bound to the wrong
scope (returning all rows for the entity) or worked accidentally. The
view did not reliably return exactly one "latest" row per entity.

Replace with a window-function pattern:

    ROW_NUMBER() OVER (PARTITION BY entity_id ORDER BY timestamp DESC)

picked out as `_rn = 1`. No correlation, no scoping ambiguity, one row
per entity by construction. Supported on PostgreSQL (always) and SQLite
≥ 3.25.

Test `test_provenance_view_uses_window_function_for_latest_per_entity`
asserts the new pattern is present and the old `MAX(p2.timestamp)`
pattern is gone.

`cargo clippy --all-targets -- -D warnings` clean; 38 unit tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: hyperpolymath

src/codegen/query.rs

@@ -180,7 +180,13 @@ fn generate_provenance_view(
         table_name
     );
 
-    // Use a subquery to get the latest provenance entry per entity.
+    // Select the latest provenance row per entity via ROW_NUMBER() over a
+    // PARTITION-by-entity / ORDER-by-timestamp-DESC window. The previous
+    // correlated MAX(timestamp) subquery referenced the outer
+    // `verisimdb_provenance_log` table by base-name, which is ambiguous
+    // when the same table appears in nested scopes and produced wrong
+    // (or no) "latest" rows depending on planner choices. Closes #40.
+    // ROW_NUMBER is supported on PostgreSQL (always) and SQLite ≥ 3.25.
     format!(
         "{comment}\
          CREATE VIEW IF NOT EXISTS verisimdb_{table_name}_with_provenance AS\n\
@@ -193,14 +199,13 @@ fn generate_provenance_view(
          FROM {table_name}\n\
          LEFT JOIN (\n\
          \x20   SELECT entity_id, operation, actor, timestamp, hash\n\
-         \x20   FROM verisimdb_provenance_log\n\
-         \x20   WHERE table_name = '{table_name}'\n\
-         \x20   AND timestamp = (\n\
-         \x20       SELECT MAX(p2.timestamp)\n\
-         \x20       FROM verisimdb_provenance_log p2\n\
-         \x20       WHERE p2.entity_id = verisimdb_provenance_log.entity_id\n\
-         \x20       AND p2.table_name = '{table_name}'\n\
-         \x20   )\n\
+         \x20   FROM (\n\
+         \x20       SELECT entity_id, operation, actor, timestamp, hash,\n\
+         \x20              ROW_NUMBER() OVER (PARTITION BY entity_id ORDER BY timestamp DESC) AS _rn\n\
+         \x20       FROM verisimdb_provenance_log\n\
+         \x20       WHERE table_name = '{table_name}'\n\
+         \x20   ) ranked\n\
+         \x20   WHERE _rn = 1\n\
          ) prov ON prov.entity_id = ({entity_id_expr});\n\n",
         columns = column_list.join(",\n"),
     )
@@ -398,6 +403,35 @@ mod tests {
         assert!(interceptor.access_filter.is_none());
     }
 
+    /// The provenance view must use a window-function `ROW_NUMBER()` pattern
+    /// instead of the old (broken) correlated MAX(timestamp) subquery.
+    /// Closes #40.
+    #[test]
+    fn test_provenance_view_uses_window_function_for_latest_per_entity() {
+        let schema = test_schema();
+        let octad = OctadConfig {
+            enable_provenance: true,
+            enable_lineage: false,
+            enable_temporal: false,
+            enable_access_control: false,
+            enable_constraints: false,
+            enable_simulation: false,
+        };
+        let interceptors = generate_interceptors(&schema, &octad, DatabaseBackend::SQLite);
+        let view = interceptors[0]
+            .provenance_view
+            .as_ref()
+            .expect("provenance view present when enabled");
+        assert!(
+            view.contains("ROW_NUMBER() OVER (PARTITION BY entity_id ORDER BY timestamp DESC)"),
+            "provenance view should use window-function latest-per-entity"
+        );
+        assert!(
+            !view.contains("MAX(p2.timestamp)"),
+            "old correlated MAX(timestamp) pattern must be gone"
+        );
+    }
+
     #[test]
     fn test_provenance_view_references_table() {
         let schema = test_schema();