feat: #37 Batch1 — detect_material_type/read_image_meta/read_text_stats/parse_text out-pointer FFI

新增 4 个 _separate 函数绕过 RustBuffer struct-passing：
- ffi_zx_document_ffi_detect_material_type_separate
- ffi_zx_document_ffi_read_image_meta_separate
- ffi_zx_document_ffi_read_text_stats_separate
- ffi_zx_document_ffi_parse_text_separate

提取 write_result_to_out! 宏和 read_str_input helper 减少样板代码。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/zx_document_ffi/src/lib.rs

@@ -242,6 +242,88 @@ fn clear_exported_events(count: u32) {
     zx_document_core::events::clear_exported_events(count as usize)
 }
 
+/// Helper: serialize a Result<T, DocumentError> into out-pointers.
+/// Generic over T; the RustBuffer methods are accessed via the concrete type
+/// after the `lower_return` call.
+macro_rules! write_result_to_out {
+    ($result:expr, $out_capacity:ident, $out_len:ident, $out_data:ident, $out_error_code:ident) => {{
+        use uniffi::LowerReturn;
+        match <Result<_, DocumentError> as LowerReturn<UniFfiTag>>::lower_return($result) {
+            Ok(buf) => {
+                unsafe {
+                    *$out_capacity = buf.capacity() as u64;
+                    *$out_len = buf.len() as u64;
+                    *$out_data = buf.data_pointer() as *mut u8;
+                    *$out_error_code = 0;
+                }
+                std::mem::forget(buf);
+            }
+            Err(_) => {
+                unsafe { *$out_error_code = -1; }
+            }
+        }
+    }};
+}
+
+/// Helper: read a UTF-8 string from raw bytes, or set error and return false.
+unsafe fn read_str_input(len: i32, data: *const u8, out_error_code: *mut i8) -> Option<String> {
+    let slice = std::slice::from_raw_parts(data, len as usize);
+    match std::str::from_utf8(slice) {
+        Ok(s) => Some(s.to_string()),
+        Err(_) => { *out_error_code = -1; None },
+    }
+}
+
+// ─── Batch 1 out-pointer functions: String input → Result<T, E> output ───
+
+#[no_mangle]
+pub extern "C" fn ffi_zx_document_ffi_detect_material_type_separate(
+    len: i32, data: *const u8,
+    out_capacity: *mut u64, out_len: *mut u64, out_data: *mut *mut u8, out_error_code: *mut i8,
+) {
+    let file_path = match unsafe { read_str_input(len, data, out_error_code) } {
+        Some(s) => s, None => return,
+    };
+    let result = crate::detect_material_type(file_path);
+    write_result_to_out!(result, out_capacity, out_len, out_data, out_error_code);
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_zx_document_ffi_read_image_meta_separate(
+    len: i32, data: *const u8,
+    out_capacity: *mut u64, out_len: *mut u64, out_data: *mut *mut u8, out_error_code: *mut i8,
+) {
+    let file_path = match unsafe { read_str_input(len, data, out_error_code) } {
+        Some(s) => s, None => return,
+    };
+    let result = crate::read_image_meta(file_path);
+    write_result_to_out!(result, out_capacity, out_len, out_data, out_error_code);
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_zx_document_ffi_read_text_stats_separate(
+    len: i32, data: *const u8,
+    out_capacity: *mut u64, out_len: *mut u64, out_data: *mut *mut u8, out_error_code: *mut i8,
+) {
+    let file_path = match unsafe { read_str_input(len, data, out_error_code) } {
+        Some(s) => s, None => return,
+    };
+    let result = crate::read_text_stats(file_path);
+    write_result_to_out!(result, out_capacity, out_len, out_data, out_error_code);
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_zx_document_ffi_parse_text_separate(
+    len: i32, data: *const u8,
+    out_capacity: *mut u64, out_len: *mut u64, out_data: *mut *mut u8, out_error_code: *mut i8,
+) {
+    let content = match unsafe { read_str_input(len, data, out_error_code) } {
+        Some(s) => s, None => return,
+    };
+    let result = crate::parse_text(content);
+    write_result_to_out!(result, out_capacity, out_len, out_data, out_error_code);
+}
+
 // Reverse conversion: FFI DocumentBlock → core DocumentBlock, used by search.
 fn core_block_from_ffi(block: DocumentBlock) -> core_blocks::DocumentBlock {
     match block {