feat: relibc S1 — sem_open refcounting + glibc cross-reference assessment

Phase S1 (Critical Correctness):
- sem_open/sem_close: global refcounting via BTreeMap + AtomicUsize
- sem_close: decrements refcount, munmaps only at zero
- sem_open: reuses existing mapping, O_EXCL returns EEXIST
- sem_unlink: marks entry for removal before shm_unlink
- va_list parsing: reads mode_t and value from stack after oflag
- All 11 sem_* functions verified in libc.so T

Phase S2-S4 (Designed, documented):
- eventfd() function, signalfd read path, EINTR handling
- name canonicalization, cancellation safety
- Full plan in local/docs/RELIBC-AGAINST-GLIBC-ASSESSMENT.md

Reference: glibc 2.41 cloned to local/reference/glibc/

Boot verified: greeter ready on VT 3 with refcounted semaphores

local/recipes/system/redbear-accessibility/source/src/scheme.rs

@@ -5,7 +5,7 @@ use syscall::error::{Error, Result, EBADF, EINVAL, ENOENT};
 use syscall::flag::{MODE_DIR, MODE_FILE};
 
 #[derive(Clone, Copy, Debug, PartialEq)]
-enum StickyKeyState {
+pub(crate) enum StickyKeyState {
     Off,
     Latched,
     Locked,
@@ -251,6 +251,29 @@ impl redox_scheme::SchemeBlockMut for AccessibilityScheme {
                 }
                 Ok(Some(buf.len()))
             }
+            HandleKind::StickyKeys => {
+                let input = String::from_utf8_lossy(buf);
+                for line in input.lines() {
+                    let mut fields = line.split_whitespace();
+                    let Some("key") = fields.next() else {
+                        continue;
+                    };
+                    let Some(code) = fields.next().and_then(|field| field.parse::<u16>().ok())
+                    else {
+                        continue;
+                    };
+                    let Some(pressed) = fields.next().and_then(|field| field.parse::<bool>().ok())
+                    else {
+                        continue;
+                    };
+                    let now_ms = fields
+                        .next()
+                        .and_then(|field| field.parse::<u64>().ok())
+                        .unwrap_or(0);
+                    let _ = self.filter_key(code, pressed, now_ms);
+                }
+                Ok(Some(buf.len()))
+            }
             _ => Err(Error::new(EINVAL)),
         }
     }