docs: document src/services/types.rs, src/modes/common.rs, and src/services/error.rs

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

src/services/error.rs

@@ -1,22 +1,44 @@
 use thiserror::Error;
 
 /// Core error types used across services for consistent error handling.
+///
+/// This enum centralizes errors from database, I/O, validation, and other operations.
+/// It implements Error and Debug for propagation and logging. Use this for all service-level errors.
+///
+/// # Variants
+///
+/// * `Database(rusqlite::Error)` - Wraps SQLite errors from queries or transactions.
+/// * `Io(std::io::Error)` - Wraps I/O errors from file operations or streams.
+/// * `ItemNotFound(i64)` - Specific item not found by ID.
+/// * `ItemNotFoundGeneric` - Generic item not found (no ID specified).
+/// * `InvalidInput(String)` - User or config input validation failure with message.
+/// * `Compression(String)` - Compression/decompression errors with details.
+/// * `Other(anyhow::Error)` - Catch-all for other anyhow-wrapped errors.
+/// * `Migration(rusqlite_migration::Error)` - Database migration failures.
 #[derive(Error, Debug)]
 pub enum CoreError {
     #[error("Database error: {0}")]
+    /// Database operation failed.
     Database(#[from] rusqlite::Error),
     #[error("I/O error: {0}")]
+    /// File or stream I/O operation failed.
     Io(#[from] std::io::Error),
     #[error("Item not found with id {0}")]
+    /// Item with the specified ID does not exist in the database.
     ItemNotFound(i64),
     #[error("Item not found")]
+    /// Item does not exist (no specific ID).
     ItemNotFoundGeneric,
     #[error("Invalid input: {0}")]
+    /// Input validation failed.
     InvalidInput(String),
     #[error("Compression error: {0}")]
+    /// Compression or decompression operation failed.
     Compression(String),
     #[error(transparent)]
+    /// Other unexpected error.
     Other(#[from] anyhow::Error),
     #[error("Migration error: {0}")]
+    /// Database schema migration failed.
     Migration(#[from] rusqlite_migration::Error),
 }