refactor: drop the dead shell probe and unused engine bindings

utils::detect_shell lost to the image probe; krun_set_root and
krun_set_env have had no caller since the root crossed as a block
device. Unused FFI bindings rot where they stand.

crates/ecrou/src/krun.rs

@@ -117,18 +117,6 @@ impl Krun {
         krun_ret(unsafe { f(ctx_id, vcpus, ram_mib) }, "krun_set_vm_config")
     }
 
-    /// `krun_set_root`: the virtiofs share that becomes the guest root.
-    pub fn set_root(&self, ctx_id: u32, root: &Path) -> Result<()> {
-        let root_c = path_cstring(root)?;
-        let f = symbol!(
-            self.lib,
-            b"krun_set_root\0",
-            unsafe extern "C" fn(u32, *const c_char) -> i32
-        );
-        // Safety: root_c is NUL-terminated and outlives the call.
-        krun_ret(unsafe { f(ctx_id, root_c.as_ptr()) }, "krun_set_root")
-    }
-
     /// `krun_add_disk`: a raw image as a virtio-blk device. An engine
     /// built without the blk feature ships no such symbol, and the
     /// lookup failure names that, not age.
@@ -264,18 +252,6 @@ impl Krun {
         )
     }
 
-    /// `krun_set_env`: extra environment for the payload.
-    pub fn set_env(&self, ctx_id: u32, envp: &[String]) -> Result<()> {
-        let envp_c = CArgs::build(envp)?;
-        let f = symbol!(
-            self.lib,
-            b"krun_set_env\0",
-            unsafe extern "C" fn(u32, *const *const c_char) -> i32
-        );
-        // Safety: envp_c is NUL-terminated and outlives the call.
-        krun_ret(unsafe { f(ctx_id, envp_c.ptr()) }, "krun_set_env")
-    }
-
     /// `krun_set_console_output`: redirect the guest console to a file.
     pub fn set_console_output(&self, ctx_id: u32, path: &Path) -> Result<()> {
         let path_c = path_cstring(path)?;
@@ -437,9 +413,9 @@ mod tests {
 
     #[test]
     fn krun_ret_maps_negated_errno() {
-        let err = krun_ret(-2, "krun_set_root").unwrap_err();
+        let err = krun_ret(-2, "krun_set_vm_config").unwrap_err();
         let msg = format!("{err:#}");
-        assert!(msg.contains("krun_set_root failed"), "{msg}");
+        assert!(msg.contains("krun_set_vm_config failed"), "{msg}");
         assert!(msg.contains("No such file"), "{msg}");
     }
 }

crates/ecrou/src/utils.rs

@@ -160,28 +160,6 @@ pub fn map_oci_arch(arch: &str) -> String {
     Arch::from_str(arch).oci_name().to_string()
 }
 
-// ============================================================================
-// Shell detection
-// ============================================================================
-
-/// Detect the best available shell in a rootfs
-/// Checks for bash first, falls back to sh
-/// Returns the path relative to the rootfs (e.g., "/bin/bash")
-pub fn detect_shell(rootfs: &Path) -> &'static str {
-    // Check for bash first (preferred)
-    if rootfs.join("bin/bash").exists() {
-        "/bin/bash"
-    } else if rootfs.join("bin/sh").exists() {
-        "/bin/sh"
-    } else if rootfs.join("usr/bin/bash").exists() {
-        "/usr/bin/bash"
-    } else if rootfs.join("usr/bin/sh").exists() {
-        "/usr/bin/sh"
-    } else {
-        "/bin/sh" // Will fail with clear error if not present
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;