Merge origin/main into auto/frame-blend-draw-path

`mesh_consistency_disc.rs` had the only conflict: this branch added a
`Sightings` type alias where #22 replaced the file's private `disc_root()`
with the shared `common::disc_root`. Both kept — they are unrelated edits
that happened to land in the same lines.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

crates/sylpheed-formats/examples/default_owners.rs

@@ -25,8 +25,12 @@ fn is_value(s: &str) -> bool {
 }
 
 fn main() {
-    let root = std::env::var("SYLPHEED_DISC")
-        .unwrap_or_else(|_| "/home/fabi/RE - Project Sylpheed/sylph_extract".into());
+    // No hardcoded fallback: it made SYLPHEED_DISC look like a control while
+    // one machine's directory layout decided the outcome (#16).
+    let Ok(root) = std::env::var("SYLPHEED_DISC") else {
+        eprintln!("set SYLPHEED_DISC to the extracted disc root");
+        std::process::exit(2);
+    };
     let wanted: Vec<String> = std::env::args().skip(1).collect();
     let arc = PakArchive::open(std::path::Path::new(&root).join("dat/GP_MAIN_GAME_E.pak")).unwrap();
 

crates/sylpheed-formats/examples/defaulted_fields.rs

@@ -31,9 +31,14 @@ fn is_value(s: &str) -> bool {
 }
 
 fn main() {
+    // argv[1], else SYLPHEED_DISC. No hardcoded fallback -- see #16.
     let root = std::env::args()
         .nth(1)
-        .unwrap_or_else(|| "/home/fabi/RE - Project Sylpheed/sylph_extract".into());
+        .or_else(|| std::env::var("SYLPHEED_DISC").ok())
+        .unwrap_or_else(|| {
+            eprintln!("usage: defaulted_fields <disc-root> [paks...]   (or set SYLPHEED_DISC)");
+            std::process::exit(2);
+        });
     let paks: Vec<String> = std::env::args().skip(2).collect();
     let paks = if paks.is_empty() {
         vec![