fix(cli): preserve stdin directory probe traces

The directory-source migration initially skipped its C probe for stdin because
stdin can never be a directory from the CLI's normal marker path. The original
C source-open callback nevertheless called `UTIL_isDirectory` for every source,
including the stdin marker, and file-stat trace tests rely on those calls being
observable.

Always invoke the private C directory probe before source opening and keep the
same positive-result rejection. This preserves the trace side effect for stdin
while retaining Rust ownership of the rejection decision and the old source
open ordering.

Test Plan:
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/Cargo.toml --all-targets -- -D warnings` -- passed
- `ulimit -v 41943040; cargo +nightly fmt --manifest-path rust/Cargo.toml --all -- --check` -- passed
- `git diff --cached --check` -- passed
- The capped upstream run exposed two stdin file-stat trace mismatches; the suite will be rerun after this compatibility fix.

rust/src/fileio_asyncio.rs

@@ -3080,13 +3080,11 @@ pub unsafe extern "C" fn FIO_rust_decompressFilename(
     assert!(!projection.dst_file_name.is_null());
     assert!(!projection.src_file_name.is_null());
 
-    if projection.source_is_stdin == 0 {
-        let source_is_directory = projection
-            .source_is_directory
-            .expect("source directory callback is required for named files");
-        if unsafe { source_is_directory(projection.opaque, projection.src_file_name) } != 0 {
-            return 1;
-        }
+    let source_is_directory = projection
+        .source_is_directory
+        .expect("source directory callback is required");
+    if unsafe { source_is_directory(projection.opaque, projection.src_file_name) } != 0 {
+        return 1;
     }
 
     let open_source = projection
@@ -6067,6 +6065,16 @@ mod tests {
         assert!(state.events.is_empty());
     }
 
+    #[test]
+    fn decompress_file_policy_probes_stdin_marker_before_opening_source() {
+        let mut state = DecompressPolicyState::default();
+        let projection = decompress_policy_projection(&mut state, 0, 0, 1, 0, 0);
+
+        assert_eq!(unsafe { FIO_rust_decompressFilename(&projection) }, 0);
+        assert_eq!(state.source_directory_checks, 1);
+        assert_eq!(state.events[0], DECOMPRESS_POLICY_OPEN_SOURCE);
+    }
+
     #[test]
     fn decompress_file_policy_orders_cleanup_and_successful_source_removal() {
         let mut state = DecompressPolicyState {