refactor(cli): move zstd frame action policy to Rust

Project the zstd frame decoder status into a Rust action classification while
preserving C-owned diagnostics, error-help formatting, private resources, and
exact decoding return values. Unknown statuses retain the assertion fallback
and the existing frame-decoding error result.

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_BUILD_JOBS=1 cargo clippy --manifest-path rust/cli/Cargo.toml --all-targets -- -D warnings` -- passed
- `ulimit -v 41943040; cargo +nightly fmt --manifest-path rust/Cargo.toml --all -- --check` -- passed
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 make -j1` -- passed
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 ./tests/rustLibSmoke` -- passed
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 make -j1 -C tests test` -- passed, including large streaming, native, fuzzer, and zstream phases

programs/fileio.c

@@ -404,6 +404,13 @@ enum {
     FIO_RUST_ZSTD_FRAME_DECODING_ERROR = 1,
     FIO_RUST_ZSTD_FRAME_PREMATURE_END = 2,
 };
+enum {
+    FIO_RUST_ZSTD_FRAME_ACTION_OK = 0,
+    FIO_RUST_ZSTD_FRAME_ACTION_DECODING_ERROR = 1,
+    FIO_RUST_ZSTD_FRAME_ACTION_PREMATURE_END = 2,
+    FIO_RUST_ZSTD_FRAME_ACTION_INVALID = 3,
+};
+int FIO_rust_decompressZstdFrameAction(int status);
 typedef void (*FIO_rust_frame_progress_fn)(void* opaque,
                                            const char* srcFileName,
                                            U64 decodedSize);
@@ -3786,23 +3793,24 @@ FIO_decompressZstdFrames(FIO_ctx_t* const fCtx, dRess_t* ress,
         fCtx, ress->dctx, ress->readCtx, ress->writeCtx, srcFileName,
         alreadyDecoded, &decodedSize, &zstdError,
         FIO_decompressZstdFrameProgress);
+    int const action = FIO_rust_decompressZstdFrameAction(status);
 
-    if (status == FIO_RUST_ZSTD_FRAME_OK)
+    switch (action) {
-        return decodedSize;
+        case FIO_RUST_ZSTD_FRAME_ACTION_OK:
-    if (status == FIO_RUST_ZSTD_FRAME_DECODING_ERROR) {
+            return decodedSize;
-        DISPLAYLEVEL(1, "%s : Decoding error (36) : %s \n",
+        case FIO_RUST_ZSTD_FRAME_ACTION_DECODING_ERROR:
-                        srcFileName, ZSTD_getErrorName(zstdError));
+            DISPLAYLEVEL(1, "%s : Decoding error (36) : %s \n",
-        FIO_zstdErrorHelp(prefs, ress, zstdError, srcFileName);
+                            srcFileName, ZSTD_getErrorName(zstdError));
-        return FIO_ERROR_FRAME_DECODING;
+            FIO_zstdErrorHelp(prefs, ress, zstdError, srcFileName);
+            return FIO_ERROR_FRAME_DECODING;
+        case FIO_RUST_ZSTD_FRAME_ACTION_PREMATURE_END:
+            DISPLAYLEVEL(1, "%s : Read error (39) : premature end \n",
+                         srcFileName);
+            return FIO_ERROR_FRAME_DECODING;
+        default:
+            assert(0);
+            return FIO_ERROR_FRAME_DECODING;
     }
-    if (status == FIO_RUST_ZSTD_FRAME_PREMATURE_END) {
-        DISPLAYLEVEL(1, "%s : Read error (39) : premature end \n",
-                     srcFileName);
-        return FIO_ERROR_FRAME_DECODING;
-    }
-
-    assert(0);
-    return FIO_ERROR_FRAME_DECODING;
 }
 
 

rust/src/fileio_prefs.rs

@@ -348,6 +348,42 @@ const FIO_RUST_ZSTD_ERROR_HELP_WINDOW_GUIDANCE: c_int = 1;
 #[cfg(feature = "decompression")]
 const FIO_RUST_ZSTD_ERROR_HELP_UNSUPPORTED_WINDOW_LOG: c_int = 2;
 
+#[cfg(feature = "decompression")]
+const FIO_RUST_ZSTD_FRAME_OK: c_int = 0;
+#[cfg(feature = "decompression")]
+const FIO_RUST_ZSTD_FRAME_DECODING_ERROR: c_int = 1;
+#[cfg(feature = "decompression")]
+const FIO_RUST_ZSTD_FRAME_PREMATURE_END: c_int = 2;
+
+#[cfg(feature = "decompression")]
+pub const FIO_RUST_ZSTD_FRAME_ACTION_OK: c_int = 0;
+#[cfg(feature = "decompression")]
+pub const FIO_RUST_ZSTD_FRAME_ACTION_DECODING_ERROR: c_int = 1;
+#[cfg(feature = "decompression")]
+pub const FIO_RUST_ZSTD_FRAME_ACTION_PREMATURE_END: c_int = 2;
+#[cfg(feature = "decompression")]
+pub const FIO_RUST_ZSTD_FRAME_ACTION_INVALID: c_int = 3;
+
+#[cfg(feature = "decompression")]
+#[inline]
+fn decompress_zstd_frame_action(status: c_int) -> c_int {
+    match status {
+        FIO_RUST_ZSTD_FRAME_OK => FIO_RUST_ZSTD_FRAME_ACTION_OK,
+        FIO_RUST_ZSTD_FRAME_DECODING_ERROR => FIO_RUST_ZSTD_FRAME_ACTION_DECODING_ERROR,
+        FIO_RUST_ZSTD_FRAME_PREMATURE_END => FIO_RUST_ZSTD_FRAME_ACTION_PREMATURE_END,
+        _ => FIO_RUST_ZSTD_FRAME_ACTION_INVALID,
+    }
+}
+
+/// Classify a zstd-frame status without owning the CLI's diagnostics or
+/// private decompression resources.  C keeps the exact messages, error-help
+/// call, and return values for each resulting action.
+#[cfg(feature = "decompression")]
+#[no_mangle]
+pub extern "C" fn FIO_rust_decompressZstdFrameAction(status: c_int) -> c_int {
+    decompress_zstd_frame_action(status)
+}
+
 #[cfg(feature = "decompression")]
 type FIO_rust_zstdErrorHelpDisplayFn =
     unsafe extern "C" fn(*mut c_void, c_int, *const c_char, u64, c_uint, c_uint, c_uint);
@@ -2460,6 +2496,37 @@ mod tests {
     use std::fs;
     use std::mem::{align_of, offset_of, size_of};
 
+    #[cfg(feature = "decompression")]
+    #[test]
+    fn decompress_zstd_frame_action_preserves_status_classes() {
+        let cases = [
+            (FIO_RUST_ZSTD_FRAME_OK, FIO_RUST_ZSTD_FRAME_ACTION_OK),
+            (
+                FIO_RUST_ZSTD_FRAME_DECODING_ERROR,
+                FIO_RUST_ZSTD_FRAME_ACTION_DECODING_ERROR,
+            ),
+            (
+                FIO_RUST_ZSTD_FRAME_PREMATURE_END,
+                FIO_RUST_ZSTD_FRAME_ACTION_PREMATURE_END,
+            ),
+            (-1, FIO_RUST_ZSTD_FRAME_ACTION_INVALID),
+            (3, FIO_RUST_ZSTD_FRAME_ACTION_INVALID),
+        ];
+
+        for (status, expected_action) in cases {
+            assert_eq!(
+                decompress_zstd_frame_action(status),
+                expected_action,
+                "unexpected action for zstd frame status {status}"
+            );
+            assert_eq!(
+                FIO_rust_decompressZstdFrameAction(status),
+                expected_action,
+                "export disagrees for zstd frame status {status}"
+            );
+        }
+    }
+
     #[test]
     fn source_exclusion_preserves_case_sensitive_suffixes_and_null_policy() {
         let cases = [