fix(peer): apply catalog portability rules in validate_relative_path

Security audit finding EXP2-SEC-03. `path_validation.rs` guarded
against traversal, UNC prefixes, drive letters and symlink escapes, but
unlike the catalog validators in lanspread-db it did not reject Windows
device names (CON, NUL, COM1..9, LPT1..9), components with a trailing
dot or space, reserved characters (`<>:"|?*`), or control characters.
On Windows, opening `NUL.txt` talks to a device and `file.txt.` is
silently rewritten to `file.txt`, so such names must never reach the
filesystem.

The catalog component validator is now exported from lanspread-db as
`validate_portable_component` and applied to every normal component in
`validate_relative_path`. The only current caller is Stream Install's
staging-path resolution, whose inputs are already canonical catalog
paths, so this changes nothing for valid archives; it removes a
divergence between two validators that are supposed to agree.

Test plan: `just test` (new cases cover device names in any position,
trailing dot/space, a reserved character and a control character, and
confirm `console.txt` and `com10.txt` stay valid).

Claude-Session: https://claude.ai/code/session_017C3Nbgwpdm3YNwZhhFLHwg

crates/lanspread-db/src/content_manifest/mod.rs

@@ -41,7 +41,7 @@ pub use model::{
     MAX_CATALOG_PATH_BYTES,
     MAX_CATALOG_TOTAL_BYTES,
 };
-pub use path::CanonicalCatalogPath;
+pub use path::{CanonicalCatalogPath, validate_portable_component};
 pub use store::{
     CATALOG_PUBLICATION_MARKER_NAME,
     CatalogManifestStore,

crates/lanspread-db/src/content_manifest/path.rs

@@ -164,6 +164,17 @@ fn validate_path(path: &str) -> eyre::Result<()> {
     Ok(())
 }
 
+/// Validates one path component under the portable catalog rules: no
+/// `.`/`..`, at most 255 bytes, no trailing dot or space, no control or
+/// Windows-reserved characters, and no Windows device name stem.
+///
+/// # Errors
+///
+/// Returns the first violated rule.
+pub fn validate_portable_component(component: &str) -> eyre::Result<()> {
+    validate_component(component)
+}
+
 fn validate_component(component: &str) -> eyre::Result<()> {
     if component.is_empty() || matches!(component, "." | "..") {
         eyre::bail!("catalog path contains a non-canonical component: {component:?}");

crates/lanspread-peer/src/path_validation.rs

@@ -1,6 +1,7 @@
 use std::path::{Component, Path, PathBuf};
 
 use eyre::WrapErr;
+use lanspread_db::content_manifest::validate_portable_component;
 
 fn canonicalize_base_dir(base_dir: &Path) -> eyre::Result<PathBuf> {
     if !base_dir.is_absolute() {
@@ -59,6 +60,16 @@ pub fn validate_relative_path(base_dir: &Path, relative_path: &str) -> eyre::Res
             }
             Component::CurDir => {}
             Component::Normal(part) => {
+                // Apply the same portability rules as the catalog manifests
+                // (Windows device names, trailing dots/spaces, reserved and
+                // control characters) so a name that the Win32 API would
+                // silently rewrite or route to a device never reaches the
+                // filesystem.
+                let component = part.to_str().ok_or_else(|| {
+                    eyre::eyre!("Path component is not valid UTF-8: {relative_path}")
+                })?;
+                validate_portable_component(component)
+                    .wrap_err_with(|| format!("Path component is not portable: {relative_path}"))?;
                 resolved.push(part);
 
                 if let Ok(metadata) = std::fs::symlink_metadata(&resolved)
@@ -132,6 +143,31 @@ mod tests {
         assert!(validate_game_file_path(base, "../../etc/passwd").is_err());
     }
 
+    #[test]
+    fn test_windows_device_names_and_trailing_dots_rejected() {
+        let temp_dir = TempDir::new("lanspread-path-validation");
+        let base = temp_dir.path();
+
+        for path in [
+            "CON",
+            "nul.txt",
+            "sub/COM1",
+            "LPT1.log",
+            "trailing.",
+            "trailing ",
+            "sub./file",
+            "bad:name",
+            "ctrl\u{7}char",
+        ] {
+            assert!(
+                validate_game_file_path(base, path).is_err(),
+                "accepted {path:?}"
+            );
+        }
+        assert!(validate_game_file_path(base, "console.txt").is_ok());
+        assert!(validate_game_file_path(base, "com10.txt").is_ok());
+    }
+
     #[test]
     fn test_double_dot_in_filename_allowed() {
         let temp_dir = TempDir::new("lanspread-path-validation");