fix: validate fuzz seed ranges without overflow

apps/solvecraft-cli/tests/fuzz_range.rs

@@ -0,0 +1,31 @@
+//! Seed ranges must not crash or wrap, including at the last representable seed.
+
+use std::process::Command;
+
+#[test]
+fn overflowing_seed_range_is_an_error_not_a_panic() {
+    let output =
+        Command::new(env!("CARGO_BIN_EXE_solvecraft-cli")).args(["fuzz", "--from", "18446744073709551615", "--count", "2"]).output().unwrap();
+    assert_eq!(output.status.code(), Some(1));
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(stderr.contains("seed range exceeds u64::MAX"), "{stderr}");
+    assert!(!stderr.contains("panicked"), "{stderr}");
+}
+
+#[test]
+fn empty_seed_range_at_maximum_is_valid() {
+    let output =
+        Command::new(env!("CARGO_BIN_EXE_solvecraft-cli")).args(["fuzz", "--from", "18446744073709551615", "--count", "0"]).output().unwrap();
+    assert!(output.status.success(), "{}", String::from_utf8_lossy(&output.stderr));
+    assert!(String::from_utf8_lossy(&output.stdout).starts_with("0 seeds, 0 design steps,"));
+}
+
+#[test]
+fn maximum_seed_runs_once_without_wrapping() {
+    let output = Command::new(env!("CARGO_BIN_EXE_solvecraft-cli"))
+        .args(["fuzz", "--from", "18446744073709551615", "--count", "1", "--steps", "0", "--timeout", "0"])
+        .output()
+        .unwrap();
+    assert!(output.status.success(), "{}", String::from_utf8_lossy(&output.stderr));
+    assert!(String::from_utf8_lossy(&output.stdout).starts_with("1 seeds,"));
+}