refactor: make shared path and cache utilities wasm-safe

Move native-only path and Tokio dependencies behind cfg gates so shared crates can compile for wasm32. Replace the absolute-path implementation with a lexical normalization fallback on wasm, use a std mutex for the cache helper on wasm, and degrade git symlink creation to an unsupported-platform error instead of a compile-time failure.

codex-rs/utils/cache/src/lib.rs

@@ -5,7 +5,13 @@ use std::num::NonZeroUsize;
 use lru::LruCache;
 use sha1::Digest;
 use sha1::Sha1;
+#[cfg(target_arch = "wasm32")]
+use std::sync::Mutex;
+#[cfg(target_arch = "wasm32")]
+use std::sync::MutexGuard;
+#[cfg(not(target_arch = "wasm32"))]
 use tokio::sync::Mutex;
+#[cfg(not(target_arch = "wasm32"))]
 use tokio::sync::MutexGuard;
 
 /// A minimal LRU cache protected by a Tokio mutex.
@@ -119,6 +125,7 @@ where
     }
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 fn lock_if_runtime<K, V>(m: &Mutex<LruCache<K, V>>) -> Option<MutexGuard<'_, LruCache<K, V>>>
 where
     K: Eq + Hash,
@@ -127,6 +134,14 @@ where
     Some(tokio::task::block_in_place(|| m.blocking_lock()))
 }
 
+#[cfg(target_arch = "wasm32")]
+fn lock_if_runtime<K, V>(m: &Mutex<LruCache<K, V>>) -> Option<MutexGuard<'_, LruCache<K, V>>>
+where
+    K: Eq + Hash,
+{
+    m.lock().ok()
+}
+
 /// Computes the SHA-1 digest of `bytes`.
 ///
 /// Useful for content-based cache keys when you want to avoid staleness
@@ -141,6 +156,7 @@ pub fn sha1_digest(bytes: &[u8]) -> [u8; 20] {
     out
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 #[cfg(test)]
 mod tests {
     use super::BlockingLruCache;