diff --git a/boot/init/src/sys.rs b/boot/init/src/sys.rs
index 2711ed6..8bc9c7b 100644
--- a/boot/init/src/sys.rs
+++ b/boot/init/src/sys.rs
@@ -22,6 +22,8 @@ pub fn mount(
     let target_c = cstr(target)?;
     let fstype_c = fstype.map(cstr).transpose()?;
     let data_c = data.map(cstr).transpose()?;
+    // SAFETY: every pointer is either a live CString for the call's duration
+    // or null (the optional fstype/data), exactly as mount(2) expects.
     let ret = unsafe {
         libc::mount(
             src_c.as_ptr(),
@@ -51,6 +53,7 @@ pub fn is_block_dev(path: &str) -> bool {
 }
 
 pub fn sethostname(name: &str) -> Result<(), String> {
+    // SAFETY: name is a live &str; sethostname(2) copies name.len() bytes.
     let ret = unsafe { libc::sethostname(name.as_ptr() as *const libc::c_char, name.len()) };
     if ret != 0 {
         return Err(format!(
@@ -68,6 +71,7 @@ pub fn switch_root(newroot: &str) -> Result<(), String> {
     std::env::set_current_dir(newroot).map_err(|err| format!("chdir {newroot}: {err}"))?;
     mount(".", "/", None, libc::MS_MOVE, None)?;
     let dot = cstr(".")?;
+    // SAFETY: dot is a live CString for the duration of the call.
     if unsafe { libc::chroot(dot.as_ptr()) } != 0 {
         return Err(format!("chroot: {}", io::Error::last_os_error()));
     }
@@ -83,6 +87,8 @@ pub fn exec_init(path: &str) -> String {
     let term_env = static_cstr("TERM=linux");
     let argv = [path_c.as_ptr(), ptr::null()];
     let envp = [path_env.as_ptr(), term_env.as_ptr(), ptr::null()];
+    // SAFETY: path_c, argv, and envp are live and NUL-terminated for the call;
+    // execve only returns on failure.
     unsafe { libc::execve(path_c.as_ptr(), argv.as_ptr(), envp.as_ptr()) };
     io::Error::last_os_error().to_string()
 }
@@ -91,6 +97,8 @@ pub fn exec_init(path: &str) -> String {
 /// cpio carries the console node; this also covers cpios built without it.
 pub fn claim_console() {
     let console = static_cstr("/dev/console");
+    // SAFETY: console is a live CString; the fd is validated (>=0) before any
+    // dup2/close and only closed when it is not already a std stream.
     unsafe {
         let fd = libc::open(console.as_ptr(), libc::O_RDWR);
         if fd >= 0 {
@@ -112,10 +120,12 @@ pub fn fatal(msg: &str, debug: bool) -> ! {
     if debug {
         if let Ok(sh) = CString::new("/bin/sh") {
             let argv = [sh.as_ptr(), ptr::null()];
+            // SAFETY: sh and argv are live and NUL-terminated for the call.
             unsafe { libc::execv(sh.as_ptr(), argv.as_ptr()) };
         }
         eprintln!("sandbox-init: no /bin/sh in this initramfs (non-debug build?)");
     }
+    // SAFETY: sync(2) and reboot(2) take no pointer arguments.
     unsafe {
         libc::sync();
         libc::reboot(libc::RB_POWER_OFF);
diff --git a/sdk/python/cocoonsandbox/conn.py b/sdk/python/cocoonsandbox/conn.py
index 6b75aa7..9190f3a 100644
--- a/sdk/python/cocoonsandbox/conn.py
+++ b/sdk/python/cocoonsandbox/conn.py
@@ -64,6 +64,7 @@ def dial_agent(addr: str, sandbox_id: str, token: str, timeout: float) -> Conn:
     Upgrade, so nothing pools or proxies underneath the byte stream."""
     host, port = addr.rsplit(":", 1)
     sock = socket.create_connection((host, int(port)), timeout=timeout)
+    reader = None
     try:
         request = (
             f"GET /v1/sandboxes/{sandbox_id}/agent HTTP/1.1\r\n"
@@ -91,5 +92,8 @@ def dial_agent(addr: str, sandbox_id: str, token: str, timeout: float) -> Conn:
             raise APIError("agent upgrade", code, body.strip() or status.strip())
         return Conn(sock, reader)
     except Exception:
+        # makefile() holds a ref on the socket; close it too or the fd lingers.
+        if reader is not None:
+            reader.close()
         sock.close()
         raise
diff --git a/sdk/python/cocoonsandbox/sandbox.py b/sdk/python/cocoonsandbox/sandbox.py
index 2424787..33980bd 100644
--- a/sdk/python/cocoonsandbox/sandbox.py
+++ b/sdk/python/cocoonsandbox/sandbox.py
@@ -32,8 +32,11 @@ def __enter__(self):
         return self
 
     def __exit__(self, *exc):
-        with contextlib.suppress(Exception):
+        try:
             self.close()
+        except Exception:
+            if exc[0] is None:  # a clean block surfaces a real release failure
+                raise
 
     def exec(self, *argv: str, cwd: str = "", env: dict | None = None,
              user: str = "", session: str = "", stdin: bytes = b"") -> str: