refactor(cli): move pass-through selection policy to Rust

Move automatic decompression pass-through selection into a pure Rust scalar policy while preserving explicit preference values, stdout probing, overwrite semantics, assertions, diagnostics, and all C-owned file/resource callbacks. The C fileio boundary now supplies only the policy inputs before constructing the existing callback projection.

Test Plan: ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/Cargo.toml --all-targets -- -D warnings; cargo clippy --manifest-path rust/cli/Cargo.toml --all-targets -- -D warnings; cargo test --manifest-path rust/cli/Cargo.toml --all-targets (188 passed); cargo +nightly fmt --manifest-path rust/Cargo.toml --all -- --check; make -j1; ./tests/rustLibSmoke; make -j1 -C tests test (all shell tests, large streaming tests, native tester, fuzzer phases, and zstream tester passed).

programs/fileio.c

@@ -471,6 +471,9 @@ int FIO_rust_finishDecompressFrames(int status,
                                     U64 decodedSize,
                                     const FIO_rust_decompress_callbacks_t* callbacks);
 int FIO_rust_decompressStatusDiagnostic(int status);
+int FIO_rust_decompressPassThroughPolicy(int passThrough,
+                                         int overwrite,
+                                         int destinationIsStdout);
 
 typedef void (*FIO_rust_decompress_read_fill_fn)(
         void* opaque, size_t requested, const unsigned char** buffer, size_t* loaded);
@@ -4216,18 +4219,14 @@ static int FIO_decompressFrames(FIO_ctx_t* const fCtx,
                                 const char* dstFileName, const char* srcFileName)
 {
     U64 filesize = 0;
-    int passThrough = prefs->passThrough;
+    int const passThrough = FIO_rust_decompressPassThroughPolicy(
+        prefs->passThrough,
+        prefs->overwrite,
+        prefs->passThrough == -1 ? !strcmp(dstFileName, stdoutmark) : 0);
     FIO_rust_decompression_projection_t projection;
     FIO_rust_decompress_callbacks_t callbacks;
     int status;
 
-    if (passThrough == -1) {
-        /* If pass-through mode is not explicitly enabled or disabled,
-         * default to the legacy behavior of enabling it if we are writing
-         * to stdout with the overwrite flag enabled.
-         */
-        passThrough = prefs->overwrite && !strcmp(dstFileName, stdoutmark);
-    }
     assert(passThrough == 0 || passThrough == 1);
 
     projection.fCtx = fCtx;

rust/src/fileio_asyncio.rs

@@ -64,6 +64,31 @@ pub const FIO_RUST_DECOMPRESS_DIAGNOSTIC_LZMA_UNSUPPORTED: c_int = 4;
 pub const FIO_RUST_DECOMPRESS_DIAGNOSTIC_LZ4_UNSUPPORTED: c_int = 5;
 pub const FIO_RUST_DECOMPRESS_DIAGNOSTIC_UNSUPPORTED_FORMAT: c_int = 6;
 
+/// Resolves the legacy automatic pass-through mode without touching the
+/// destination name or any C-owned file state.  Explicit values are returned
+/// unchanged so the C assertion keeps its original validation behavior.
+#[inline]
+fn decompress_pass_through_policy(
+    pass_through: c_int,
+    overwrite: c_int,
+    destination_is_stdout: c_int,
+) -> c_int {
+    if pass_through == -1 {
+        (overwrite != 0 && destination_is_stdout != 0) as c_int
+    } else {
+        pass_through
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn FIO_rust_decompressPassThroughPolicy(
+    pass_through: c_int,
+    overwrite: c_int,
+    destination_is_stdout: c_int,
+) -> c_int {
+    decompress_pass_through_policy(pass_through, overwrite, destination_is_stdout)
+}
+
 /// Maps decompression results to the diagnostics that the C CLI displays.
 /// Statuses without a legacy diagnostic deliberately map to `NONE`, retaining
 /// the previous C callback's silent default case.
@@ -5299,6 +5324,25 @@ impl PoolInner {
 mod tests {
     use super::*;
 
+    #[test]
+    fn decompression_pass_through_policy_preserves_explicit_and_default_modes() {
+        for pass_through in [0, 1] {
+            assert_eq!(
+                decompress_pass_through_policy(pass_through, 0, 0),
+                pass_through
+            );
+            assert_eq!(
+                decompress_pass_through_policy(pass_through, 1, 1),
+                pass_through
+            );
+        }
+
+        assert_eq!(decompress_pass_through_policy(-1, 0, 0), 0);
+        assert_eq!(decompress_pass_through_policy(-1, 0, 1), 0);
+        assert_eq!(decompress_pass_through_policy(-1, 1, 0), 0);
+        assert_eq!(decompress_pass_through_policy(-1, 1, 1), 1);
+    }
+
     #[test]
     fn decompression_status_diagnostic_preserves_cli_mapping() {
         for (status, diagnostic) in [