docs: Add rustdoc for filter_plugin, binary_detection, and lib.rs

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

src/common/binary_detection.rs

@@ -17,6 +17,39 @@ use std::collections::HashMap;
 /// * `Result<(), StatusCode>` - 
 ///     * `Ok(())` if binary content is allowed or content is not binary
 ///     * `Err(StatusCode::BAD_REQUEST)` if binary content is not allowed and content is binary
+/// Check if content is binary when allow_binary is false
+///
+/// Validates whether binary content is permitted for the item. If not allowed and content
+/// is detected as binary, returns a bad request status. Uses metadata or streams content
+/// for detection if needed.
+///
+/// # Arguments
+///
+/// * `item_service` - Reference to the async item service for content access.
+/// * `item_id` - The ID of the item to check.
+/// * `metadata` - Metadata associated with the item (checked for "text" key).
+/// * `allow_binary` - Whether binary content is allowed (bypasses check if true).
+///
+/// # Returns
+///
+/// * `Result<(), StatusCode>` - 
+///     * `Ok(())` if binary content is allowed or content is not binary.
+///     * `Err(StatusCode::BAD_REQUEST)` if binary content is not allowed and content is binary.
+///
+/// # Errors
+///
+/// Propagates `StatusCode` for validation failures.
+///
+/// # Examples
+///
+/// ```
+/// // If allow_binary = false and content is text
+/// check_binary_content_allowed(&service, 1, &metadata, false)?;
+/// // Succeeds
+///
+/// // If allow_binary = false and content is binary
+/// // Returns Err(StatusCode::BAD_REQUEST)
+/// ```
 pub async fn check_binary_content_allowed(
     item_service: &AsyncItemService,
     item_id: i64,
@@ -46,6 +79,34 @@ pub async fn check_binary_content_allowed(
 ///     * `Ok(true)` if content is binary
 ///     * `Ok(false)` if content is text
 ///     * `Err(StatusCode)` if an error occurs during checking
+/// Helper function to determine if content is binary
+///
+/// Checks existing "text" metadata first; if absent or unset, streams and analyzes
+/// the content to detect binary nature. Logs warnings on detection failures.
+///
+/// # Arguments
+///
+/// * `item_service` - Reference to the async item service for content access.
+/// * `item_id` - The ID of the item to check.
+/// * `metadata` - Metadata associated with the item (checked for "text" key).
+///
+/// # Returns
+///
+/// * `Result<bool, StatusCode>` - 
+///     * `Ok(true)` if content is binary.
+///     * `Ok(false)` if content is text.
+///     * `Err(StatusCode)` if an error occurs during checking (e.g., INTERNAL_SERVER_ERROR).
+///
+/// # Errors
+///
+/// * `StatusCode::INTERNAL_SERVER_ERROR` if content access fails.
+///
+/// # Examples
+///
+/// ```
+/// let is_bin = is_content_binary(&service, 1, &metadata).await?;
+/// assert!(is_bin == false); // For text content
+/// ```
 pub async fn is_content_binary(
     item_service: &AsyncItemService,
     item_id: i64,