engine: replace base_from with from_salsa constructor

src/simlin-engine/CLAUDE.md

@@ -32,7 +32,7 @@ Equation text flows through these stages in order:
 - **`src/variable.rs`** - Variable variants (`Stock`, `Flow`, `Aux`, `Module`), `ModuleInput`, `Table` (graphical functions). `classify_dependencies()` is the primary API for extracting dependency categories from an AST in a single walk, returning a `DepClassification` with five sets: `all` (every referenced ident), `init_referenced`, `previous_referenced`, `previous_only` (idents only inside PREVIOUS), and `init_only` (idents only inside INIT/PREVIOUS). The older single-purpose functions (`identifier_set`, `init_referenced_idents`, etc.) remain as thin wrappers. `parse_var_with_module_context` accepts a `module_idents` set so `PREVIOUS(module_var)` falls through to module expansion instead of `LoadPrev`.
 - **`src/dimensions.rs`** - Dimension context and dimension matching for arrays
 - **`src/model.rs`** - Model compilation stages (`ModelStage0` -> `ModelStage1` -> `ModuleStage2`), dependency resolution, topological sort. `collect_module_idents` pre-scans datamodel variables to identify which names will expand to modules (preventing incorrect `LoadPrev` compilation). `init_referenced_vars` extends the Initials runlist to include variables referenced by `INIT()` calls, ensuring their values are captured in the `initial_values` snapshot. `check_units` is gated behind `cfg(any(test, feature = "testing"))` (production unit checking uses salsa tracked functions).
-- **`src/project.rs`** - `Project` struct aggregating models. `From<datamodel::Project>`, `with_ltm()`, and `with_ltm_all_links()` are all gated behind `cfg(any(test, feature = "testing"))` (monolithic construction path, retained only for tests and the AST interpreter cross-validation path); production code uses `db::compile_project_incremental` with `ltm_enabled`/`ltm_discovery_mode` on `SourceProject`.
+- **`src/project.rs`** - `Project` struct aggregating models. `from_salsa(datamodel, db, source_project, cb)` builds a Project from a pre-synced salsa database (all variable parsing comes from salsa-cached results). `from_datamodel(datamodel)` is a convenience wrapper that creates a local DB and syncs. `From<datamodel::Project>`, `with_ltm()`, and `with_ltm_all_links()` are all gated behind `cfg(any(test, feature = "testing"))` (retained only for tests and the AST interpreter cross-validation path); production code uses `db::compile_project_incremental` with `ltm_enabled`/`ltm_discovery_mode` on `SourceProject`.
 - **`src/results.rs`** - `Results` (variable offsets + timeseries data), `Specs` (time/integration config)
 - **`src/patch.rs`** - `ModelPatch`/`ProjectPatch` for representing and applying model changes
 

src/simlin-engine/src/db.rs

@@ -689,11 +689,11 @@ pub fn project_units_context(db: &dyn Db, project: SourceProject) -> crate::unit
         Err(unit_parse_errors) => {
             // Accumulate each unit definition parsing error as a
             // project-level diagnostic (no model / variable).
-            for (_unit_name, eq_errors) in &unit_parse_errors {
+            for (unit_name, eq_errors) in &unit_parse_errors {
                 for eq_err in eq_errors {
                     CompilationDiagnostic(Diagnostic {
                         model: String::new(),
-                        variable: None,
+                        variable: Some(unit_name.clone()),
                         error: DiagnosticError::Unit(crate::common::UnitError::DefinitionError(
                             eq_err.clone(),
                             None,

src/simlin-engine/src/model.rs

@@ -872,6 +872,7 @@ pub(crate) fn equation_is_stdlib_call(eqn: &datamodel::Equation) -> bool {
 }
 
 #[cfg(any(test, feature = "testing"))]
+#[allow(dead_code)]
 impl ModelStage0 {
     pub fn new(
         x_model: &datamodel::Model,