feat(compress): move advanced CDict compression orchestration into Rust

Move deprecated advanced CDict one-shot validation and begin-then-end ordering
behind a Rust-owned boundary while preserving the explicit frame policy. Keep
the private CDict begin and end operations in C callbacks.

Test Plan:
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo test --manifest-path rust/Cargo.toml --release compress_using_cdict_advanced -- --nocapture
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo test --manifest-path rust/Cargo.toml --release
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/Cargo.toml --release --all-targets -- -D warnings
- ulimit -v 41943040; make -B -C programs -j1 zstd
- ulimit -v 41943040; make -C tests -j1 test-zstream ZSTREAM_TESTTIME=-T1s

lib/compress/zstd_compress.c

@@ -1499,6 +1499,30 @@ typedef char ZSTD_rust_compress_using_cdict_state_layout[
                 == 3 * sizeof(void*)
          && sizeof(ZSTD_rust_compressUsingCDictState) == 4 * sizeof(void*))
         ? 1 : -1];
+typedef struct {
+    void* callbackContext;
+    const void* cdict;
+    const ZSTD_frameParameters* fParams;
+    ZSTD_rust_compressUsingCDictBegin_f begin;
+    ZSTD_rust_compressUsingCDictEnd_f end;
+} ZSTD_rust_compressUsingCDictAdvancedState;
+size_t ZSTD_rust_compressUsingCDictAdvanced(
+        const ZSTD_rust_compressUsingCDictAdvancedState* state,
+        void* dst, size_t dstCapacity,
+        const void* src, size_t srcSize);
+typedef char ZSTD_rust_compress_using_cdict_advanced_state_layout[
+        (offsetof(ZSTD_rust_compressUsingCDictAdvancedState, callbackContext) == 0
+         && offsetof(ZSTD_rust_compressUsingCDictAdvancedState, cdict)
+                == sizeof(void*)
+         && offsetof(ZSTD_rust_compressUsingCDictAdvancedState, fParams)
+                == 2 * sizeof(void*)
+         && offsetof(ZSTD_rust_compressUsingCDictAdvancedState, begin)
+                == 3 * sizeof(void*)
+         && offsetof(ZSTD_rust_compressUsingCDictAdvancedState, end)
+                == 4 * sizeof(void*)
+         && sizeof(ZSTD_rust_compressUsingCDictAdvancedState)
+                == 5 * sizeof(void*))
+        ? 1 : -1];
 typedef size_t (*ZSTD_rust_compressBeginUsingCDictPublicBegin_f)(
         void* context, const void* cdict,
         const ZSTD_frameParameters* fParams, U64 pledgedSrcSize);
@@ -5851,18 +5875,6 @@ size_t ZSTD_compressBegin_usingCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict)
     return ZSTD_compressBegin_usingCDict_deprecated(cctx, cdict);
 }
 
-/*! ZSTD_compress_usingCDict_internal():
- * Implementation of various ZSTD_compress_usingCDict* functions.
- */
-static size_t ZSTD_compress_usingCDict_internal(ZSTD_CCtx* cctx,
-                                void* dst, size_t dstCapacity,
-                                const void* src, size_t srcSize,
-                                const ZSTD_CDict* cdict, ZSTD_frameParameters fParams)
-{
-    FORWARD_IF_ERROR(ZSTD_compressBegin_usingCDict_internal(cctx, cdict, fParams, srcSize), ""); /* will check if cdict != NULL */
-    return ZSTD_compressEnd_public(cctx, dst, dstCapacity, src, srcSize);
-}
-
 static size_t ZSTD_rust_compressUsingCDict_begin(
         void* context, const void* cdict,
         const ZSTD_frameParameters* fParams, U64 pledgedSrcSize)
@@ -5888,7 +5900,14 @@ size_t ZSTD_compress_usingCDict_advanced(ZSTD_CCtx* cctx,
                                 const void* src, size_t srcSize,
                                 const ZSTD_CDict* cdict, ZSTD_frameParameters fParams)
 {
-    return ZSTD_compress_usingCDict_internal(cctx, dst, dstCapacity, src, srcSize, cdict, fParams);
+    ZSTD_rust_compressUsingCDictAdvancedState state;
+    state.callbackContext = cctx;
+    state.cdict = cdict;
+    state.fParams = &fParams;
+    state.begin = ZSTD_rust_compressUsingCDict_begin;
+    state.end = ZSTD_rust_compressUsingCDict_end;
+    return ZSTD_rust_compressUsingCDictAdvanced(
+            &state, dst, dstCapacity, src, srcSize);
 }
 
 /*! ZSTD_compress_usingCDict() :

rust/src/zstd_compress_dictionary.rs

@@ -300,6 +300,68 @@ pub unsafe extern "C" fn ZSTD_rust_compressUsingCDict(
     unsafe { (state.end)(state.callback_context, dst, dst_capacity, src, src_size) }
 }
 
+/// Explicit projection for the deprecated public
+/// `ZSTD_compress_usingCDict_advanced` wrapper.
+///
+/// Rust owns CDict validation and begin-then-end ordering while C retains the
+/// private begin and end operations behind callbacks.
+#[repr(C)]
+pub struct ZSTD_rust_compressUsingCDictAdvancedState {
+    callback_context: *mut c_void,
+    cdict: *const c_void,
+    f_params: *const ZSTD_frameParameters,
+    begin: CompressUsingCDictBeginFn,
+    end: CompressUsingCDictEndFn,
+}
+
+const _: () = {
+    assert!(offset_of!(ZSTD_rust_compressUsingCDictAdvancedState, callback_context) == 0);
+    assert!(offset_of!(ZSTD_rust_compressUsingCDictAdvancedState, cdict) == size_of::<usize>());
+    assert!(
+        offset_of!(ZSTD_rust_compressUsingCDictAdvancedState, f_params) == 2 * size_of::<usize>()
+    );
+    assert!(offset_of!(ZSTD_rust_compressUsingCDictAdvancedState, begin) == 3 * size_of::<usize>());
+    assert!(offset_of!(ZSTD_rust_compressUsingCDictAdvancedState, end) == 4 * size_of::<usize>());
+    assert!(size_of::<ZSTD_rust_compressUsingCDictAdvancedState>() == size_of::<[usize; 5]>());
+};
+
+/// Compress a complete source using an explicit CDict frame policy.
+#[no_mangle]
+pub unsafe extern "C" fn ZSTD_rust_compressUsingCDictAdvanced(
+    state: *const ZSTD_rust_compressUsingCDictAdvancedState,
+    dst: *mut c_void,
+    dst_capacity: usize,
+    src: *const c_void,
+    src_size: usize,
+) -> usize {
+    if state.is_null() {
+        return ERROR(ZstdErrorCode::Generic);
+    }
+    let state = unsafe { &*state };
+    if state.callback_context.is_null() {
+        return ERROR(ZstdErrorCode::Generic);
+    }
+    if state.cdict.is_null() {
+        return ERROR(ZstdErrorCode::DictionaryWrong);
+    }
+    if state.f_params.is_null() {
+        return ERROR(ZstdErrorCode::Generic);
+    }
+
+    let begin_result = unsafe {
+        (state.begin)(
+            state.callback_context,
+            state.cdict,
+            state.f_params,
+            src_size as u64,
+        )
+    };
+    if ERR_isError(begin_result) {
+        return begin_result;
+    }
+    unsafe { (state.end)(state.callback_context, dst, dst_capacity, src, src_size) }
+}
+
 type CompressBeginUsingCDictPublicBeginFn =
     unsafe extern "C" fn(*mut c_void, *const c_void, *const ZSTD_frameParameters, u64) -> usize;
 
@@ -2779,6 +2841,78 @@ mod tests {
         assert_eq!(probe.events, ["begin"]);
     }
 
+    fn compress_using_cdict_advanced_test_state(
+        probe: &mut CompressUsingCDictProbe,
+        cdict: *const c_void,
+        f_params: &ZSTD_frameParameters,
+    ) -> ZSTD_rust_compressUsingCDictAdvancedState {
+        ZSTD_rust_compressUsingCDictAdvancedState {
+            callback_context: (probe as *mut CompressUsingCDictProbe).cast(),
+            cdict,
+            f_params,
+            begin: compress_using_cdict_test_begin,
+            end: compress_using_cdict_test_end,
+        }
+    }
+
+    #[test]
+    fn compress_using_cdict_advanced_preserves_frame_policy_and_begin_end_order() {
+        let mut probe = CompressUsingCDictProbe {
+            end_result: 41,
+            ..Default::default()
+        };
+        let cdict = ptr::dangling::<c_void>();
+        let f_params = ZSTD_frameParameters {
+            contentSizeFlag: 0,
+            checksumFlag: 1,
+            noDictIDFlag: 1,
+        };
+        let state = compress_using_cdict_advanced_test_state(&mut probe, cdict, &f_params);
+        let mut dst = [0u8; 4];
+        let src = [9u8, 8];
+
+        let result = unsafe {
+            ZSTD_rust_compressUsingCDictAdvanced(
+                &state,
+                dst.as_mut_ptr().cast(),
+                dst.len(),
+                src.as_ptr().cast(),
+                src.len(),
+            )
+        };
+
+        assert_eq!(result, probe.end_result);
+        assert_eq!(probe.events, ["begin", "end"]);
+        assert_eq!(probe.cdict, cdict);
+        assert_eq!(probe.frame_params.contentSizeFlag, 0);
+        assert_eq!(probe.frame_params.checksumFlag, 1);
+        assert_eq!(probe.frame_params.noDictIDFlag, 1);
+        assert_eq!(probe.pledged_src_size, src.len() as u64);
+        assert_eq!(probe.dst, dst.as_mut_ptr().cast());
+        assert_eq!(probe.dst_capacity, dst.len());
+        assert_eq!(probe.src, src.as_ptr().cast());
+        assert_eq!(probe.src_size, src.len());
+    }
+
+    #[test]
+    fn compress_using_cdict_advanced_rejects_a_missing_frame_policy_before_callback() {
+        let mut probe = CompressUsingCDictProbe::default();
+        let state = ZSTD_rust_compressUsingCDictAdvancedState {
+            callback_context: (&mut probe as *mut CompressUsingCDictProbe).cast(),
+            cdict: ptr::dangling(),
+            f_params: ptr::null(),
+            begin: compress_using_cdict_test_begin,
+            end: compress_using_cdict_test_end,
+        };
+
+        let result = unsafe {
+            ZSTD_rust_compressUsingCDictAdvanced(&state, ptr::null_mut(), 0, ptr::null(), 0)
+        };
+
+        assert_eq!(result, ERROR(ZstdErrorCode::Generic));
+        assert!(probe.events.is_empty());
+    }
+
     fn compress_begin_using_cdict_public_test_state(
         probe: &mut CompressUsingCDictProbe,
         cdict: *const c_void,