diff --git a/.config/nextest.toml b/.config/nextest.toml
index d393c69b..66fe1043 100644
--- a/.config/nextest.toml
+++ b/.config/nextest.toml
@@ -3,7 +3,8 @@
 
 [profile.ci]
 # Heavy tests (one to four minutes each on a CI runner) that pull requests skip. They run on
-# every push to main and nightly (`--ignore-default-filter`), and in `cargo xtask test`.
+# every push to main and nightly (`--ignore-default-filter`), and in `cargo xtask test`. The
+# boolean_props property tests run only nightly (ci.yml excludes them from pushes to main).
 # Keep this list in sync with docs/book/src/dev/testing.md and CONTRIBUTING.md.
 default-filter = """
 not (
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5b676912..8b523826 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -229,7 +229,11 @@ jobs:
         run: |
           # Pull requests skip the heavy tests (default-filter in .config/nextest.toml).
           all=()
-          if [ "$EVENT_NAME" != pull_request ]; then all=(--ignore-default-filter); fi
+          # The boolean property tests draw new random inputs every run; they run only in the
+          # nightly property-tests job, so a known kernel bug cannot turn main red at random.
+          if [ "$EVENT_NAME" != pull_request ]; then
+            all=(--ignore-default-filter -E 'not (package(solidcraft-kernel) & binary(boolean_props))')
+          fi
           # Extract into ./target: tests that run a built binary (env!("CARGO_BIN_EXE_*")) have
           # the build job's path, which is the same checkout path here.
           cargo nextest run --archive-file tests.tar.zst --workspace-remap . --extract-to . --extract-overwrite \
@@ -319,7 +323,8 @@ jobs:
 
   property-tests:
     # The boolean property tests and the atomic command tests with many cases. Pull requests skip
-    # them (.config/nextest.toml); pushes to main run them with small defaults (8 cases, seeds 0..4).
+    # them (.config/nextest.toml); pushes to main run atomic_commands with small defaults (seeds
+    # 0..4) and skip boolean_props, whose random inputs would fail main at random.
     name: Property tests (many cases)
     needs: build-tests
     if: github.event_name == 'schedule' || github.event_name == 'workflow_dispatch'
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 095a61af..b835ed41 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -181,7 +181,8 @@ Pull requests skip a few heavy tests (one to four minutes each), which run on ev
   `pattern_suppress_tests::enclosure_arc_extinction_keeps_a_real_sharp_inner_lip_after_resize_and_reopen`,
   `pattern_suppress_tests::enclosure_datums_follow_wall_height_and_board_depth_with_material_proofs`,
   `cmd::plastic::tests::enclosure_snap_fit_follows_resized_front_wall`, the `atomic_commands` contract tests
-- `solidcraft-kernel`: `tests::boolean_identity_on_tangent_primitives`, the `boolean_props` property tests
+- `solidcraft-kernel`: `tests::boolean_identity_on_tangent_primitives`, and the `boolean_props` property tests
+  (these run only in the nightly "Property tests" job: their inputs are random, so main skips them too)
 - `solidcraft-ui-egui` scenarios: `acceptance_sensor_enclosure`
 
 **The action matrix** tries every ordinary action on every face, edge, vertex and body of a
diff --git a/crates/kernel/tests/boolean_props.rs b/crates/kernel/tests/boolean_props.rs
index fadecae7..57a7d465 100644
--- a/crates/kernel/tests/boolean_props.rs
+++ b/crates/kernel/tests/boolean_props.rs
@@ -4,10 +4,13 @@
 //! inputs, and when a case fails it shrinks the inputs to a small case that still fails. Paste
 //! that case into a normal `#[test]` as a regression test.
 //!
-//! Case count: `PROPTEST_CASES` (default 8). Pull requests skip this file (.config/nextest.toml);
-//! pushes to main run it, and the nightly `property-tests` job uses more cases. A long local run:
+//! Case count: `PROPTEST_CASES` (default 8). Pull requests and pushes to main skip this file
+//! (.config/nextest.toml, .github/workflows/ci.yml): its random inputs differ on every run, so a
+//! known kernel bug would turn main red at random. The nightly `property-tests` job runs it with
+//! more cases. A long local run:
 //! `PROPTEST_CASES=2000 cargo test -p solidcraft-kernel --test boolean_props`.
-//! proptest saves every failing seed in `tests/boolean_props.proptest-regressions`. Commit it.
+//! proptest saves every failing seed in `tests/boolean_props.proptest-regressions`. Commit it, and
+//! copy the shrunk case into a `#[test]` below (ignored, with its issue, until the kernel is fixed).
 
 use proptest::prelude::*;
 use solidcraft_geom::Vec3;
@@ -102,7 +105,15 @@ fn cfg(default: u32) -> ProptestConfig {
     // The env var overrides the default; proptest reads PROPTEST_CASES itself only when the
     // config does not set `cases`, so read it here.
     let cases = std::env::var("PROPTEST_CASES").ok().and_then(|s| s.parse().ok()).unwrap_or(default);
-    ProptestConfig { cases, max_shrink_iters: 200, ..ProptestConfig::default() }
+    // Integration tests have no lib.rs or main.rs beside them, so proptest's default persistence
+    // cannot place its file; name it.
+    let file = concat!(env!("CARGO_MANIFEST_DIR"), "/tests/boolean_props.proptest-regressions");
+    ProptestConfig {
+        cases,
+        max_shrink_iters: 200,
+        failure_persistence: Some(Box::new(prop::test_runner::FileFailurePersistence::Direct(file))),
+        ..ProptestConfig::default()
+    }
 }
 
 proptest! {
@@ -218,3 +229,44 @@ proptest! {
         prop_assert!(close(run(&plate, &boss, BoolOp::Union)?, vp + vb, vp + vb), "plate + boss lost or gained volume");
     }
 }
+
+// Cases the property tests found, as plain tests. Ignored until the kernel bug is fixed: run them
+// with `cargo test -p solidcraft-kernel --test boolean_props -- --ignored`.
+
+fn check(r: Result<(), TestCaseError>) {
+    if let Err(e) = r {
+        panic!("{e}");
+    }
+}
+
+/// A box and a cylinder in general position: the intersect is refused as an implausible volume.
+#[test]
+#[ignore = "kernel bug, #1647"]
+fn generic_box_cylinder_intersect() {
+    let a = Prim::Box { at: [11.483767761089219, 4.801612107504224, 3.6313476467611787], size: [4.789088988834864, 3.0, 10.419335961063835] };
+    let b = Prim::Cyl { at: [29.2480632732879, 8.3683289461485, 6.947922225984966], axis: 2, r: 13.502884497756853, h: 19.719218725477496 };
+    check(identity(&a, &b));
+}
+
+/// A sphere and a box on the grid: the union has a face that does not mesh.
+#[test]
+#[ignore = "kernel bug, #1648"]
+fn grid_sphere_box_union_is_sound() {
+    let a = Prim::Sph { at: [2.5, 15.0, 27.5], r: 12.5 };
+    let b = Prim::Box { at: [0.0, 0.0, 17.5], size: [5.0, 7.5, 5.0] };
+    check(identity(&a, &b));
+}
+
+/// Two crossing cylinders: the union moved 1000 mm away loses about a tenth of its volume.
+#[test]
+#[ignore = "kernel bug, #1649"]
+fn crossing_cylinders_union_moved_far() {
+    let a = Prim::Cyl { at: [17.5, 30.0, 7.5], axis: 0, r: 5.0, h: 10.0 }.body();
+    let b = Prim::Cyl { at: [17.5, 30.0, 15.0], axis: 1, r: 12.5, h: 5.0 }.body();
+    let t = Vec3::new(1000.0, -700.0, 300.0);
+    let mv = |x: &Body| transform(x, t, Vec3::ZERO, Vec3::Z, 0.0).expect("translate");
+    let s = vol(&a) + vol(&b);
+    let here = run(&a, &b, BoolOp::Union).unwrap();
+    let there = run(&mv(&a), &mv(&b), BoolOp::Union).unwrap();
+    assert!(close(here, there, s), "union at origin {here:.4}, moved by 1000 gives {there:.4}");
+}
diff --git a/docs/book/src/dev/testing.md b/docs/book/src/dev/testing.md
index 105160b5..e275dc42 100644
--- a/docs/book/src/dev/testing.md
+++ b/docs/book/src/dev/testing.md
@@ -81,7 +81,8 @@ Pull requests skip a few heavy tests (each takes one to four minutes); they run
   `pattern_suppress_tests::enclosure_arc_extinction_keeps_a_real_sharp_inner_lip_after_resize_and_reopen`,
   `pattern_suppress_tests::enclosure_datums_follow_wall_height_and_board_depth_with_material_proofs`,
   `cmd::plastic::tests::enclosure_snap_fit_follows_resized_front_wall`, the `atomic_commands` contract tests
-- `solidcraft-kernel`: `tests::boolean_identity_on_tangent_primitives`, the `boolean_props` property tests
+- `solidcraft-kernel`: `tests::boolean_identity_on_tangent_primitives`, and the `boolean_props` property tests
+  (these run only in the nightly "Property tests" job: their inputs are random, so main skips them too)
 - `solidcraft-ui-egui` scenarios: `acceptance_sensor_enclosure`
 
 The **action matrix** (`apps/solidcraft-cli/tests/action_matrix.rs`) tries every ordinary action