docs: Add comprehensive rustdoc to save mode functions and types

Co-authored-by: aider (openai/andrew/openrouter/sonoma-sky-alpha) <aider@aider.chat>

src/modes/save.rs

@@ -5,6 +5,19 @@ use std::io::{Read, Write};
 use crate::config;
 use crate::services::item_service::ItemService;
 
+/// Validates save mode arguments and exits with error if invalid.
+///
+/// This function checks that no item IDs are provided for save mode,
+/// as save operations create new items rather than modifying existing ones.
+///
+/// # Arguments
+///
+/// * `cmd` - Mutable reference to the Clap command for error reporting.
+/// * `ids` - Reference to the vector of item IDs (should be empty for save mode).
+///
+/// # Panics
+///
+/// Exits the program via Clap error if IDs are provided.
 fn validate_save_args(cmd: &mut Command, ids: &Vec<i64>) {
     if !ids.is_empty() {
         cmd.error(
@@ -15,13 +28,51 @@ fn validate_save_args(cmd: &mut Command, ids: &Vec<i64>) {
     }
 }
 
-// Tee reader that writes to a writer as it is read
+/// A tee reader that duplicates input to both a reader and a writer as it reads.
+///
+/// This struct implements the `Read` trait and forwards all read operations to
+/// an underlying reader while simultaneously writing the same data to a writer.
+/// It's useful for saving content to a file while also echoing it to stdout.
+///
+/// # Fields
+///
+/// * `reader` - The underlying reader providing the data source.
+/// * `writer` - The writer receiving copies of all read data.
 struct TeeReader<R: Read, W: Write> {
     reader: R,
     writer: W,
 }
 
 impl<R: Read, W: Write> Read for TeeReader<R, W> {
+    /// Reads data from the underlying reader and duplicates it to the writer.
+    ///
+    /// This implementation reads from the inner reader and then writes the same
+    /// bytes to the writer. If the read returns 0 bytes (EOF), it returns 0.
+    ///
+    /// # Arguments
+    ///
+    /// * `buf` - Buffer to fill with data from the reader.
+    ///
+    /// # Returns
+    ///
+    /// * `io::Result<usize>` - Number of bytes read, or an I/O error.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the underlying read or write operations fail.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut tee = TeeReader {
+    ///     reader: std::io::Cursor::new(b"Hello, world!"),
+    ///     writer: std::io::sink(),
+    /// };
+    /// let mut buf = [0; 5];
+    /// let n = tee.read(&mut buf).unwrap();
+    /// assert_eq!(n, 5);
+    /// assert_eq!(&buf[..n], b"Hello");
+    /// ```
     fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
         let n = self.reader.read(buf)?;
         if n > 0 {
@@ -31,6 +82,32 @@ impl<R: Read, W: Write> Read for TeeReader<R, W> {
     }
 }
 
+/// Main save mode function.
+///
+/// This function handles the save operation by reading from stdin, duplicating
+/// the input to stdout (for real-time display), and saving the content to the
+/// item service. It validates arguments, creates the tee reader, and processes
+/// the save operation.
+///
+/// # Arguments
+///
+/// * `cmd` - Mutable reference to the Clap command for error handling.
+/// * `settings` - Application settings containing configuration.
+/// * `ids` - Mutable vector of item IDs (should be empty for save mode).
+/// * `tags` - Mutable vector of tags to associate with the new item.
+/// * `conn` - Mutable reference to the database connection.
+/// * `data_path` - Path to the data storage directory.
+///
+/// # Returns
+///
+/// * `Result<(), anyhow::Error>` - Success or error if save fails.
+///
+/// # Examples
+///
+/// ```
+/// // In CLI context, this would be called internally
+/// mode_save(&mut cmd, &settings, &mut vec![], &mut vec!["important".to_string()], &mut conn, data_path)?;
+/// ```
 pub fn mode_save(
     cmd: &mut Command,
     settings: &config::Settings,