fix: demote path-not-exists validation errors to debug

The /image cross-library fallback tries the resolved library first and falls
back to any library holding the rel_path. The first attempt emitted error-level
noise on every grid tile in union mode. Split the validation error so only
traversal attempts log at error; missing-file cases log at debug.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/files.rs

@@ -1,6 +1,6 @@
 use ::anyhow;
 use actix::{Handler, Message};
-use anyhow::{Context, anyhow};
+use anyhow::Context;
 use std::collections::HashSet;
 use std::fmt::Debug;
 use std::fs::read_dir;
@@ -1024,33 +1024,58 @@ pub fn is_valid_full_path<P: AsRef<Path> + Debug + AsRef<std::ffi::OsStr>>(
 
     match is_path_above_base_dir(base, &mut path, new_file) {
         Ok(path) => Some(path),
-        Err(e) => {
+        Err(PathValidationError::DoesNotExist(p)) => {
+            debug!("Path does not exist under base {:?}: {:?}", base, p);
+            None
+        }
+        Err(PathValidationError::AboveBase(p)) => {
+            error!("Path above base directory {:?}: {:?}", base, p);
+            None
+        }
+        Err(PathValidationError::Other(e)) => {
             error!("{}", e);
             None
         }
     }
 }
 
+#[derive(Debug)]
+enum PathValidationError {
+    DoesNotExist(PathBuf),
+    AboveBase(PathBuf),
+    Other(anyhow::Error),
+}
+
+impl std::fmt::Display for PathValidationError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            PathValidationError::DoesNotExist(p) => write!(f, "Path does not exist: {:?}", p),
+            PathValidationError::AboveBase(p) => write!(f, "Path above base directory: {:?}", p),
+            PathValidationError::Other(e) => write!(f, "{}", e),
+        }
+    }
+}
+
 fn is_path_above_base_dir<P: AsRef<Path> + Debug>(
     base: P,
     full_path: &mut PathBuf,
     new_file: bool,
-) -> anyhow::Result<PathBuf> {
-    full_path
-        .absolutize()
-        .with_context(|| format!("Unable to resolve absolute path: {:?}", full_path))
-        .map_or_else(
-            |e| Err(anyhow!(e)),
-            |p| {
-                if p.starts_with(base) && (new_file || p.exists()) {
-                    Ok(p.into_owned())
-                } else if !p.exists() {
-                    Err(anyhow!("Path does not exist: {:?}", p))
-                } else {
-                    Err(anyhow!("Path above base directory"))
-                }
-            },
-        )
+) -> Result<PathBuf, PathValidationError> {
+    match full_path.absolutize() {
+        Err(e) => Err(PathValidationError::Other(
+            anyhow::Error::new(e)
+                .context(format!("Unable to resolve absolute path: {:?}", full_path)),
+        )),
+        Ok(p) => {
+            if p.starts_with(base) && (new_file || p.exists()) {
+                Ok(p.into_owned())
+            } else if !p.exists() {
+                Err(PathValidationError::DoesNotExist(p.into_owned()))
+            } else {
+                Err(PathValidationError::AboveBase(p.into_owned()))
+            }
+        }
+    }
 }
 
 /// Handler for GPS summary endpoint
@@ -1289,6 +1314,7 @@ impl Handler<RefreshThumbnailsMessage> for StreamActor {
 mod tests {
     use super::*;
     use crate::database::DbError;
+    use ::anyhow::anyhow;
     use std::collections::HashMap;
     use std::env;
     use std::fs::File;