absorb: 27 orphaned relibc patches re-applied (Phase 1.0A)

Per local/docs/PATCH-PRESERVATION-AUDIT-2026-07-12.md the relibc
fork was carrying only 34 of 90 patches in local/patches/relibc/.
The other 56 patches' content was silently missing from the fork.

This commit re-applies 27 patches that genuinely still apply
cleanly. Recovery covers:

- eventfd implementation (sys/eventfd.h + eventfd.rs)
- signalfd implementation (sys/signalfd.h + signalfd.rs)
- timerfd implementation (sys/timerfd.h + timerfd.rs)
- bits/eventfd.h header
- spawn() function: cbindgen + stdint fix
- P3-timerfd-cbindgen-fix
- cbindgen language=C fixes for sys/{timerfd,semaphore}
- stdint include chain fixes
- strtold implementation
- dns aaaa getaddrinfo ipv6
- various stack/threading/header threading fixes
- dup3 syscalls
- waitid implementation
- bits/timespec reverse_from
- open_memstream integration

24 files changed.

src/header/unistd/mod.rs

@@ -287,7 +287,20 @@ pub extern "C" fn dup2(fildes: c_int, fildes2: c_int) -> c_int {
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/dup.html>.
 // #[unsafe(no_mangle)]
 pub extern "C" fn dup3(fildes: c_int, fildes2: c_int, flag: c_int) -> c_int {
-    unimplemented!();
+    // dup3 requires fildes != fildes2 (unlike dup2 which is a no-op in that case)
+    if fildes == fildes2 {
+        ERRNO.set(EINVAL);
+        return -1;
+    }
+    match Sys::dup2(fildes, fildes2) {
+        Ok(newfd) => {
+            if flag & fcntl::O_CLOEXEC != 0 {
+                let _ = Sys::fcntl(newfd, fcntl::F_SETFD, fcntl::FD_CLOEXEC as c_ulonglong);
+            }
+            newfd
+        }
+        Err(Errno(e)) => { ERRNO.set(e); -1 }
+    }
 }
 
 // See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/encrypt.html>.
@@ -560,8 +573,39 @@ pub extern "C" fn getegid() -> gid_t {
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/getentropy.html>.
 // #[unsafe(no_mangle)]
-pub extern "C" fn getentropy(buffer: *mut c_void, length: size_t) -> c_int {
-    unimplemented!();
+pub unsafe extern "C" fn getentropy(buffer: *mut c_void, length: size_t) -> c_int {
+    // POSIX limits getentropy to 256 bytes per call
+    const GETENTROPY_MAX: size_t = 256;
+
+    if length > GETENTROPY_MAX {
+        ERRNO.set(EINVAL);
+        return -1;
+    }
+
+    let path = unsafe { CStr::from_ptr(c"/scheme/rand".as_ptr().cast()) };
+    let fd = match Sys::open(path, fcntl::O_RDONLY, 0) {
+        Ok(fd) => fd,
+        Err(Errno(e)) => {
+            ERRNO.set(e);
+            return -1;
+        }
+    };
+
+    let buf = unsafe { slice::from_raw_parts_mut(buffer.cast::<u8>(), length) };
+    let mut filled = 0usize;
+    while filled < length {
+        match Sys::read(fd, &mut buf[filled..]) {
+            Ok(0) => break,
+            Ok(n) => filled += n,
+            Err(Errno(e)) => {
+                let _ = Sys::close(fd);
+                ERRNO.set(e);
+                return -1;
+            }
+        }
+    }
+    let _ = Sys::close(fd);
+    if filled < length { ERRNO.set(errno::EIO); -1 } else { 0 }
 }
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/geteuid.html>.
@@ -1321,7 +1365,7 @@ pub extern "C" fn usleep(useconds: useconds_t) -> c_int {
 #[deprecated]
 // #[unsafe(no_mangle)]
 pub extern "C" fn vfork() -> pid_t {
-    unimplemented!();
+    unsafe { fork() }
 }
 
 unsafe fn with_argv(