Fast PR CI: small hostile-test caps, heavy tests in a separate job (#43)

* test: hostile-params test runs under small session work caps

Session gains Limits, the defaults of mesh.tet.generate's max_steiner and
max_tets (production values unchanged; a parameter still overrides them;
file.open keeps them). The registry-wide hostile-params test runs on
sessions with small caps, so the needle-triangle tessellation it meshes is
refused at once instead of meshing to the 50k Steiner cap: the engine test
binary drops from ~350 s to ~20 s locally.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* ci: move heavy tests to a heavy job on main, nightly and on demand

Four slow tests are #[ignore = "heavy: ..."] (every corpus recipe, the
cantilever convergence study, the explicit-vs-modal cantilever period, the
generic-predicate rational cross-check); fast representative tests of each
area stay in the PR gate. cargo xtask test --heavy runs every ignored test
(benchmarks included) and the doc tests; cargo xtask test and ci run the
rest without the doc tests. The new heavy CI job runs it on pushes to main,
nightly and on workflow_dispatch. Branch jobs restore main's rust cache and
no longer save their own. AGENTS.md documents the rule.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* test: the three slow LBM verification cases run in the heavy job

The Stokes-drag sphere array, the staircase-pipe convergence study and the
developing-channel case are heavy (21 s, 11 s, 6 s alone); plane
Poiseuille, Couette, Taylor-Green, reproducibility and the stability
limits stay in the PR gate.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

---------

Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/file.rs

@@ -154,9 +154,11 @@ impl Session {
         (session, warnings)
     }
 
-    /// Replace this session with `opened`, keeping its undo memory limit; the history starts empty.
+    /// Replace this session with `opened`, keeping its undo memory limit and its work caps; the
+    /// history starts empty.
     fn replace_with(&mut self, mut opened: Session) {
         opened.history = std::mem::take(&mut self.history);
+        opened.limits = self.limits;
         opened.clear_history();
         *self = opened;
     }

crates/engine/src/cmd/mesh.rs

@@ -126,10 +126,9 @@ fn surface_options(p: &Value, mesh: &SurfaceMesh) -> Result<SurfaceOptions> {
 }
 
 fn tet_generate(s: &mut Session, p: &Value) -> Result<Value> {
-    let defaults = CdtOptions::default();
     let cdt_options = CdtOptions {
-        max_steiner: optional_count(p, "max_steiner", defaults.max_steiner as u64, 0..=TET_MAX_STEINER)?,
-        max_tets: optional_count(p, "max_tets", defaults.max_tets as u64, 1..=TET_MAX_TETS)?,
+        max_steiner: optional_count(p, "max_steiner", s.limits.max_steiner as u64, 0..=TET_MAX_STEINER)?,
+        max_tets: optional_count(p, "max_tets", s.limits.max_tets as u64, 1..=TET_MAX_TETS)?,
     };
     let (surface, body, face_names) = {
         let Input { mesh, body, faces } = surface_input(s, p)?;
@@ -648,6 +647,26 @@ mod tests {
         assert_eq!((s.journal.len(), &s.model), (journal, &model), "failures change nothing");
     }
 
+    /// The session's caps are the defaults of `max_steiner` and `max_tets`; a parameter overrides them.
+    #[test]
+    fn tet_generate_honours_the_session_caps() {
+        use std::sync::Arc;
+
+        use modelcraft_geometry::open_design;
+        use modelcraft_geometry::sample::{Plate, plate_design};
+
+        use crate::{EngineError, Limits};
+
+        let design = Arc::new(open_design(&plate_design(&Plate::default()).unwrap()).unwrap());
+        let mut s = Session { design: Some(design), limits: Limits { max_tets: 10, ..Limits::default() }, ..Session::default() };
+        let plate = json!({"body": "Body1", "tolerance": 0.5});
+        let refused = s.execute("mesh.tet.generate", &plate).unwrap_err();
+        assert!(matches!(refused, EngineError::Mesh(modelcraft_mesh::Error::Limit(_))), "{refused}");
+        assert!(s.model.elements().is_empty());
+        let r = s.execute("mesh.tet.generate", &json!({"body": "Body1", "tolerance": 0.5, "max_tets": 1_000_000})).unwrap();
+        assert!(r["elements"].as_u64().unwrap() > 0, "{r}");
+    }
+
     #[test]
     fn tet_generate_on_an_imported_surface_and_an_open_one() {
         use std::sync::Arc;

crates/engine/src/cmd/solve.rs

@@ -792,6 +792,7 @@ pub(crate) mod tests {
     /// bending energy, so without hourglass stiffness (viscous control) the period is longer by
     /// (1 − 1/n²)^{−½} (3.3% for n = 4); the stiffness form restores part of it.
     #[test]
+    #[ignore = "heavy: cargo xtask test --heavy (CI heavy job)"]
     fn explicit_cantilever_period_matches_the_modal_frequency() {
         let (length, n) = (10.0, [40usize, 4usize]);
         let mut s = Session::default();