refactor: name the output/input paths passed to OutSink

OutSink::open_with_options took two adjacent positional Option<&Path>
parameters (output_file, input_file). The type system cannot tell them
apart, so a future call site that swaps them still compiles - and the
same-file-aliasing guard would then check the wrong path, silently
re-enabling the accidental-overwrite protection bypass it exists to
prevent. All three current call sites were correct; this hardens the
signature before a wrong one appears.

Introduce OutSinkPaths, a struct with named output_file/input_file
fields, so every call site must label which path plays which role.

No behavior change.

Test plan: cargo clippy (default/--tests) clean; cargo test passes
all 56 tests.

src/crypto.rs

@@ -179,8 +179,10 @@ pub fn encrypt(
     let plaintext_length = input.length;
     let mut f_plain = AheadReader::from(input.reader, chunk_sz);
     let mut f_encrypted = OutSink::open_with_options(
-        options.output_file.as_deref(),
-        options.input_file.as_deref(),
+        OutSinkPaths {
+            output_file: options.output_file.as_deref(),
+            input_file: options.input_file.as_deref(),
+        },
         &options.output,
     )?;
 
@@ -292,8 +294,10 @@ pub fn decrypt(
 
     let mut f_encrypted = AheadReader::from(reader, cipher_chunk);
     let mut f_plain = OutSink::open_with_options(
-        options.output_file.as_deref(),
-        options.input_file.as_deref(),
+        OutSinkPaths {
+            output_file: options.output_file.as_deref(),
+            input_file: options.input_file.as_deref(),
+        },
         &options.output,
     )?;
 
@@ -423,8 +427,10 @@ pub fn decrypt_range(
     let last_idx = n_chunks - 1;
 
     let mut out = OutSink::open_with_options(
-        options.output_file.as_deref(),
-        Some(&options.input_file),
+        OutSinkPaths {
+            output_file: options.output_file.as_deref(),
+            input_file: Some(&options.input_file),
+        },
         &options.output,
     )?;
 

src/utils.rs

@@ -198,6 +198,16 @@ fn output_aliases_input(output: &Path, input: Option<&Path>) -> io::Result<bool>
     }
 }
 
+/// Paths for [`OutSink::open_with_options`], named so the output and input
+/// roles cannot be swapped silently at a call site (both are `Option<&Path>`).
+pub(crate) struct OutSinkPaths<'a> {
+    /// Where the finished output is renamed to; `None` means stdout.
+    pub output_file: Option<&'a Path>,
+    /// The input being read; only consulted by the aliasing guard that
+    /// permits in-place overwrite of the input without `--force`.
+    pub input_file: Option<&'a Path>,
+}
+
 /// Output sink that supports atomic file replacement.
 ///
 /// For file outputs: bytes are written to a private, randomly named temp file.
@@ -219,11 +229,10 @@ pub(crate) enum OutSink {
 
 impl OutSink {
     pub(crate) fn open_with_options(
-        output_file: Option<&Path>,
-        input_file: Option<&Path>,
+        paths: OutSinkPaths<'_>,
         options: &OutputOptions,
     ) -> io::Result<Self> {
-        match output_file {
+        match paths.output_file {
             None if options.buffer_verify_stdout => {
                 let dir = temp_dir_for_stdout(options.temp_dir.as_deref());
                 Ok(Self::BufferVerify {
@@ -235,7 +244,7 @@ impl OutSink {
                 let final_path = f.to_path_buf();
                 if final_path.exists()
                     && !options.force
-                    && !output_aliases_input(&final_path, input_file)?
+                    && !output_aliases_input(&final_path, paths.input_file)?
                 {
                     return Err(io::Error::new(
                         io::ErrorKind::AlreadyExists,