diff --git a/crates/pinakes-core/src/media_type/builtin.rs b/crates/pinakes-core/src/media_type/builtin.rs
index 67f1d68..bd84aca 100644
--- a/crates/pinakes-core/src/media_type/builtin.rs
+++ b/crates/pinakes-core/src/media_type/builtin.rs
@@ -61,9 +61,40 @@ pub enum MediaCategory {
 }
 
 impl BuiltinMediaType {
-  /// Get the unique ID for this media type
-  pub fn id(&self) -> String {
-    format!("{:?}", self).to_lowercase()
+  /// Get the unique, stable ID for this media type.
+  pub fn id(&self) -> &'static str {
+    match self {
+      Self::Mp3 => "mp3",
+      Self::Flac => "flac",
+      Self::Ogg => "ogg",
+      Self::Wav => "wav",
+      Self::Aac => "aac",
+      Self::Opus => "opus",
+      Self::Mp4 => "mp4",
+      Self::Mkv => "mkv",
+      Self::Avi => "avi",
+      Self::Webm => "webm",
+      Self::Pdf => "pdf",
+      Self::Epub => "epub",
+      Self::Djvu => "djvu",
+      Self::Markdown => "markdown",
+      Self::PlainText => "plaintext",
+      Self::Jpeg => "jpeg",
+      Self::Png => "png",
+      Self::Gif => "gif",
+      Self::Webp => "webp",
+      Self::Svg => "svg",
+      Self::Avif => "avif",
+      Self::Tiff => "tiff",
+      Self::Bmp => "bmp",
+      Self::Cr2 => "cr2",
+      Self::Nef => "nef",
+      Self::Arw => "arw",
+      Self::Dng => "dng",
+      Self::Orf => "orf",
+      Self::Rw2 => "rw2",
+      Self::Heic => "heic",
+    }
   }
 
   /// Get the display name for this media type
diff --git a/crates/pinakes-core/src/media_type/mod.rs b/crates/pinakes-core/src/media_type/mod.rs
index 7c5ed9f..9d221c5 100644
--- a/crates/pinakes-core/src/media_type/mod.rs
+++ b/crates/pinakes-core/src/media_type/mod.rs
@@ -1,6 +1,6 @@
-//! Extensible media type system
+//! Media types
 //!
-//! This module provides an extensible media type system that supports both
+//! Supports both
 //! built-in media types and plugin-registered custom types.
 
 use std::path::Path;
@@ -13,7 +13,7 @@ pub mod registry;
 pub use builtin::{BuiltinMediaType, MediaCategory};
 pub use registry::{MediaTypeDescriptor, MediaTypeRegistry};
 
-/// Media type identifier - can be either built-in or custom
+/// Media type identifier, can be either built-in or custom
 #[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
 #[serde(untagged)]
 pub enum MediaType {
@@ -33,7 +33,7 @@ impl MediaType {
   /// Get the type ID as a string
   pub fn id(&self) -> String {
     match self {
-      Self::Builtin(b) => b.id(),
+      Self::Builtin(b) => b.id().to_string(),
       Self::Custom(id) => id.clone(),
     }
   }
@@ -61,8 +61,8 @@ impl MediaType {
   }
 
   /// Get the category for this media type
-  /// For custom types without a registry, returns MediaCategory::Document as
-  /// default
+  /// For custom types without a registry, returns [`MediaCategory::Document`]
+  /// as default
   pub fn category(&self) -> MediaCategory {
     match self {
       Self::Builtin(b) => b.category(),
@@ -192,7 +192,7 @@ impl MediaType {
   }
 }
 
-// Implement From<BuiltinMediaType> for easier conversion
+// Implement `From<BuiltinMediaType>` for easier conversion
 impl From<BuiltinMediaType> for MediaType {
   fn from(builtin: BuiltinMediaType) -> Self {
     Self::Builtin(builtin)
diff --git a/crates/pinakes-core/src/thumbnail.rs b/crates/pinakes-core/src/thumbnail.rs
index 60d4e37..7dd7852 100644
--- a/crates/pinakes-core/src/thumbnail.rs
+++ b/crates/pinakes-core/src/thumbnail.rs
@@ -12,6 +12,25 @@ use crate::{
   model::MediaId,
 };
 
+/// RAII guard that removes a file on drop.
+struct TempFileGuard(PathBuf);
+
+impl TempFileGuard {
+  fn new(path: PathBuf) -> Self {
+    Self(path)
+  }
+
+  fn path(&self) -> &Path {
+    &self.0
+  }
+}
+
+impl Drop for TempFileGuard {
+  fn drop(&mut self) {
+    let _ = std::fs::remove_file(&self.0);
+  }
+}
+
 /// Generate a thumbnail for a media file and return the path to the thumbnail.
 ///
 /// Supports images (via `image` crate), videos (via ffmpeg), PDFs (via
@@ -145,7 +164,6 @@ fn generate_pdf_thumbnail(
   dest: &Path,
   config: &ThumbnailConfig,
 ) -> Result<()> {
-  // Use pdftoppm to render first page, then resize with image crate
   let temp_prefix = dest.with_extension("tmp");
   let status = Command::new("pdftoppm")
     .args(["-jpeg", "-f", "1", "-l", "1", "-singlefile"])
@@ -167,11 +185,10 @@ fn generate_pdf_thumbnail(
     )));
   }
 
-  // pdftoppm outputs <prefix>.jpg
-  let rendered = temp_prefix.with_extension("jpg");
-  if rendered.exists() {
-    // Resize to thumbnail size
-    let img = image::open(&rendered).map_err(|e| {
+  // pdftoppm outputs <prefix>.jpg -- guard ensures cleanup on all paths
+  let rendered = TempFileGuard::new(temp_prefix.with_extension("jpg"));
+  if rendered.path().exists() {
+    let img = image::open(rendered.path()).map_err(|e| {
       PinakesError::MetadataExtraction(format!("pdf thumbnail open: {e}"))
     })?;
     let thumb = img.thumbnail(config.size, config.size);
@@ -183,7 +200,7 @@ fn generate_pdf_thumbnail(
     thumb.write_with_encoder(encoder).map_err(|e| {
       PinakesError::MetadataExtraction(format!("pdf thumbnail encode: {e}"))
     })?;
-    let _ = std::fs::remove_file(&rendered);
+    // Guard drops here and cleans up the temp file
     Ok(())
   } else {
     Err(PinakesError::MetadataExtraction(
@@ -235,12 +252,11 @@ fn generate_raw_thumbnail(
   dest: &Path,
   config: &ThumbnailConfig,
 ) -> Result<()> {
-  // Try dcraw to extract embedded JPEG preview, then resize
-  let temp_ppm = dest.with_extension("ppm");
+  let temp_ppm = TempFileGuard::new(dest.with_extension("ppm"));
   let status = Command::new("dcraw")
     .args(["-e", "-c"])
     .arg(source)
-    .stdout(std::fs::File::create(&temp_ppm).map_err(|e| {
+    .stdout(std::fs::File::create(temp_ppm.path()).map_err(|e| {
       PinakesError::MetadataExtraction(format!(
         "failed to create temp file: {e}"
       ))
@@ -254,18 +270,15 @@ fn generate_raw_thumbnail(
     })?;
 
   if !status.success() {
-    let _ = std::fs::remove_file(&temp_ppm);
+    // Guard drops and cleans up temp_ppm
     return Err(PinakesError::MetadataExtraction(format!(
       "dcraw exited with status {}",
       status
     )));
   }
 
-  // The extracted preview is typically a JPEG; try loading it
-  if temp_ppm.exists() {
-    let result = image::open(&temp_ppm);
-    let _ = std::fs::remove_file(&temp_ppm);
-    let img = result.map_err(|e| {
+  if temp_ppm.path().exists() {
+    let img = image::open(temp_ppm.path()).map_err(|e| {
       PinakesError::MetadataExtraction(format!("raw preview decode: {e}"))
     })?;
     let thumb = img.thumbnail(config.size, config.size);
@@ -277,6 +290,7 @@ fn generate_raw_thumbnail(
     thumb.write_with_encoder(encoder).map_err(|e| {
       PinakesError::MetadataExtraction(format!("raw thumbnail encode: {e}"))
     })?;
+    // Guard drops and cleans up temp_ppm
     Ok(())
   } else {
     Err(PinakesError::MetadataExtraction(
@@ -290,11 +304,10 @@ fn generate_heic_thumbnail(
   dest: &Path,
   config: &ThumbnailConfig,
 ) -> Result<()> {
-  // Use heif-convert to convert to JPEG, then resize
-  let temp_jpg = dest.with_extension("tmp.jpg");
+  let temp_jpg = TempFileGuard::new(dest.with_extension("tmp.jpg"));
   let status = Command::new("heif-convert")
     .arg(source)
-    .arg(&temp_jpg)
+    .arg(temp_jpg.path())
     .stdout(std::process::Stdio::null())
     .stderr(std::process::Stdio::null())
     .status()
@@ -305,17 +318,15 @@ fn generate_heic_thumbnail(
     })?;
 
   if !status.success() {
-    let _ = std::fs::remove_file(&temp_jpg);
+    // Guard drops and cleans up temp_jpg
     return Err(PinakesError::MetadataExtraction(format!(
       "heif-convert exited with status {}",
       status
     )));
   }
 
-  if temp_jpg.exists() {
-    let result = image::open(&temp_jpg);
-    let _ = std::fs::remove_file(&temp_jpg);
-    let img = result.map_err(|e| {
+  if temp_jpg.path().exists() {
+    let img = image::open(temp_jpg.path()).map_err(|e| {
       PinakesError::MetadataExtraction(format!("heic decode: {e}"))
     })?;
     let thumb = img.thumbnail(config.size, config.size);
@@ -327,6 +338,7 @@ fn generate_heic_thumbnail(
     thumb.write_with_encoder(encoder).map_err(|e| {
       PinakesError::MetadataExtraction(format!("heic thumbnail encode: {e}"))
     })?;
+    // Guard drops and cleans up temp_jpg
     Ok(())
   } else {
     Err(PinakesError::MetadataExtraction(
@@ -449,14 +461,11 @@ pub fn extract_epub_cover(epub_path: &Path) -> Result<Option<Vec<u8>>> {
 
 /// Extract full-size cover from a PDF file (first page)
 pub fn extract_pdf_cover(pdf_path: &Path) -> Result<Option<Vec<u8>>> {
-  // Use pdftoppm to extract the first page at high resolution
-  let pdftoppm = "pdftoppm";
-
   let temp_dir = std::env::temp_dir();
   let temp_prefix =
     temp_dir.join(format!("pdf_cover_{}", uuid::Uuid::new_v4()));
 
-  let status = Command::new(pdftoppm)
+  let status = Command::new("pdftoppm")
     .args(["-jpeg", "-f", "1", "-l", "1", "-scale-to", "1200"])
     .arg(pdf_path)
     .arg(&temp_prefix)
@@ -472,13 +481,15 @@ pub fn extract_pdf_cover(pdf_path: &Path) -> Result<Option<Vec<u8>>> {
     )));
   }
 
-  // pdftoppm outputs files like prefix-1.jpg
-  let output_path = format!("{}-1.jpg", temp_prefix.display());
-  let output_pathbuf = PathBuf::from(&output_path);
+  // pdftoppm outputs files like prefix-1.jpg -- guard ensures cleanup
+  let output = TempFileGuard::new(PathBuf::from(format!(
+    "{}-1.jpg",
+    temp_prefix.display()
+  )));
 
-  if output_pathbuf.exists() {
-    let data = std::fs::read(&output_pathbuf)?;
-    let _ = std::fs::remove_file(&output_pathbuf);
+  if output.path().exists() {
+    let data = std::fs::read(output.path())?;
+    // Guard drops and cleans up the temp file
     Ok(Some(data))
   } else {
     Ok(None)