fix: restore mcp flexibility and improve cli tooling

crates/owlen-cli/build.rs

@@ -0,0 +1,31 @@
+use std::process::Command;
+
+fn main() {
+    const MIN_VERSION: (u32, u32, u32) = (1, 75, 0);
+
+    let rustc = std::env::var("RUSTC").unwrap_or_else(|_| "rustc".into());
+    let output = Command::new(&rustc)
+        .arg("--version")
+        .output()
+        .expect("failed to invoke rustc");
+
+    let version_line = String::from_utf8_lossy(&output.stdout);
+    let version_str = version_line.split_whitespace().nth(1).unwrap_or("0.0.0");
+    let sanitized = version_str.split('-').next().unwrap_or(version_str);
+
+    let mut parts = sanitized
+        .split('.')
+        .map(|part| part.parse::<u32>().unwrap_or(0));
+    let current = (
+        parts.next().unwrap_or(0),
+        parts.next().unwrap_or(0),
+        parts.next().unwrap_or(0),
+    );
+
+    if current < MIN_VERSION {
+        panic!(
+            "owlen requires rustc {}.{}.{} or newer (found {version_line})",
+            MIN_VERSION.0, MIN_VERSION.1, MIN_VERSION.2
+        );
+    }
+}