docs: Add Rustdoc to gzip and user meta plugins, mark PLAN.md tasks done

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

src/compression_engine/gzip.rs

@@ -27,6 +27,11 @@ use flate2::write::GzEncoder;
 use crate::compression_engine::CompressionEngine;
 
 #[derive(Debug, Eq, PartialEq, Clone, Default)]
+/// GZip compression engine implementation.
+///
+/// This struct provides GZip compression and decompression capabilities using the
+/// `flate2` crate. It implements the `CompressionEngine` trait for integration
+/// with the keep system's compression framework.
 pub struct CompressionEngineGZip {}
 
 impl CompressionEngineGZip {
@@ -119,7 +124,7 @@ impl CompressionEngine for CompressionEngineGZip {
     /// let writer = engine.create("/path/to/file.gz".into()).expect("Create failed");
     /// ```
     fn create(&self, file_path: PathBuf) -> Result<Box<dyn Write>> {
-        debug!("COMPRESSION: Writting to {:?} using {:?}", file_path, *self);
+        debug!("COMPRESSION: Writing to {:?} using {:?}", file_path, *self);
 
         let file = File::create(file_path)?;
         let gzip_write = GzEncoder::new(file, Compression::default());
@@ -128,6 +133,11 @@ impl CompressionEngine for CompressionEngineGZip {
     }
 }
 
+#[derive(Debug)]
+/// Wrapper around `GzEncoder` that automatically finishes the compression stream on drop.
+///
+/// This ensures that the GZip trailer is written even if the encoder is dropped without
+/// an explicit `finish()` call, preventing corrupted output files.
 pub struct AutoFinishGzEncoder<W: Write> {
     encoder: Option<GzEncoder<W>>,
 }