Robustness runs and the kernel fixes they found

- solvecraft-cli fuzz / fuzz-one: seeded random modelling sessions (boxes, extruded profiles with arcs, revolves; joins and cuts of boxes, cylinders and spheres, fillets, chamfers, shells, holes, patterns) on a grid that makes coincident faces and tangencies common, every step checked (command ok, every body a sound solid via the new Body::validity, volume moving the right way), plus the boolean volume identity on random primitives; one process per seed with a time limit; failures minimised to scripts
- shell/offset: corners where a curved face meets another at an angle are refined onto the moved surfaces (Newton); edges that are neither lines nor arcs are rebuilt through their moved points; one shell per piece; faces that would cross say so (not supported yet) instead of leaving a cavity inside out; flat revolved faces count as planes; the unhealed body is tried when the healed one fails
- cylinders start their seams at an odd angle (grid-aligned seams broke booleans along them)
- partial revolves of profiles touching the axis build no zero-area face on the axis
- booleans on bodies in several pieces retry a piece at a time
- regression tests for each, and a fixed set of seeds in cargo test

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

apps/solvecraft-cli/src/main.rs

@@ -16,6 +16,7 @@
 #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
 #![forbid(unsafe_code)]
 
+mod fuzz;
 mod oracle;
 mod recipe;
 mod seams;
@@ -35,6 +36,7 @@ const USAGE: &str = "usage:
   solvecraft-cli commands
   solvecraft-cli recipe <recipe.json>
   solvecraft-cli oracle <case-dir>... [--json]
+  solvecraft-cli fuzz [--from N] [--count N] [--jobs J] [--timeout S] [--steps N] [--minimise] [--out DIR] [--report FILE]
   solvecraft-cli step-corpus <case-dir>... [--json]
   solvecraft-cli mcp [--in design.solvecraft|script.json] [--connect 127.0.0.1:PORT]
   solvecraft-cli licences
@@ -58,6 +60,8 @@ fn main() -> ExitCode {
         }),
         Some("oracle") => oracle::run(&args[1..]),
         Some("step-corpus") => oracle::step_corpus(&args[1..]),
+        Some("fuzz") => fuzz::run(&args[1..]),
+        Some("fuzz-one") => fuzz::one(&args[1..]),
         Some("mcp") => cmd_mcp(&args[1..]),
         Some("icon") => cmd_icon(&args[1..]),
         Some("licences" | "licenses") => {