fix: dup_into closes existing fd before inserting (POSIX dup3 semantics)

dup_into previously returned EEXIST when the target fd slot was already
occupied, causing procmgr panics during bootstrap. The fix matches dup2
behavior: close the target fd first, then insert the new one.

Also removes diagnostic crate::info! logging added during root cause
investigation of the FD table desync between userspace FILETABLE and
kernel posix_fdtbl.

src/context/context.rs

@@ -854,15 +854,6 @@ impl FdTbl {
             self.active_count += 1;
             Some(i)
         } else {
-            crate::info!("insert_file EEXIST: index={:#x} real_index={} fdtbl.len()={} is_upper={} posix_fdtbl.len()={} upper_fdtbl.len()={} active_count={}", index, real_index, fdtbl.len(), index & UPPER_FDTBL_TAG != 0, self.posix_fdtbl.len(), self.upper_fdtbl.len(), self.active_count);
-            // Dump the posix fdtbl contents
-            for (i, slot) in self.posix_fdtbl.iter().enumerate() {
-                if slot.is_some() {
-                    crate::info!("  posix_fdtbl[{}] = Some(<file>)", i);
-                } else {
-                    crate::info!("  posix_fdtbl[{}] = None", i);
-                }
-            }
             None
         }
     }

src/syscall/fs.rs

@@ -309,34 +309,28 @@ pub fn dup(fd: FileHandle, buf: UserSliceRo, token: &mut CleanLockToken) -> Resu
 }
 
 /// Duplicate a file descriptor, placing into a specific fd slot (upstream 0.9.0).
+/// If the target slot is occupied, the existing descriptor is closed first
+/// (POSIX `dup3` semantics, consistent with `dup2` below).
 pub fn dup_into(
     fd: FileHandle,
     new_cd: FileHandle,
     buf: UserSliceRo,
     token: &mut CleanLockToken,
 ) -> Result<FileHandle> {
-    crate::info!("dup_into: fd={:#x} new_cd={:#x} buf_len={}", fd.get(), new_cd.get(), buf.len());
-    let new_file = match duplicate_file(fd, buf, false, token) {
-        Ok(f) => f,
-        Err(e) => {
-            crate::info!("dup_into: duplicate_file failed: {}", e);
-            return Err(e);
-        }
-    };
-    crate::info!("dup_into: duplicate_file ok, inserting at new_cd={:#x}", new_cd.get());
+    if fd == new_cd {
+        return Ok(new_cd);
+    }
+
+    let _ = close(new_cd, token);
+
+    let new_file = duplicate_file(fd, buf, false, token)?;
+
     let current_lock = context::current();
     let mut current = current_lock.read(token.token());
     let (context, mut token) = current.token_split();
-    match context.insert_file(new_cd, new_file, &mut token) {
-        Some(h) => {
-            crate::info!("dup_into: insert ok, handle={:#x}", h.get());
-            Ok(h)
-        }
-        None => {
-            crate::info!("dup_into: insert_file returned None (EEXIST)");
-            Err(Error::new(EEXIST))
-        }
-    }
+    context
+        .insert_file(new_cd, new_file, &mut token)
+        .ok_or(Error::new(EMFILE))
 }
 
 /// Duplicate file descriptor, replacing another