re: coverage is 96.4% (6069/6294) -- and the 225 misses get a gate breakdown

undecoded.rs supplies the denominator the coverage numbers never had; the disc
holds 6294 XBG7 resources, 6069 decode, 225 are searched and missed, 0 lack a
descriptor. gate_histogram.rs attributes each miss to the furthest gate its best
candidate reached: 120 connectivity, 74 grouped-pool (different path), 15
degenerate/extent, 9 winding, 7 buffer-not-covered. Recorded as a work-list, not
a verdict -- a wrong candidate can pass more gates than the true block.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/sylpheed-formats/examples/undecoded.rs

@@ -0,0 +1,56 @@
+//! Which XBG7 resources never decode, and how big is that population?
+//!
+//! Coverage has been reported as "resources decoded" without a denominator. This
+//! prints both, per container and in total, and names the misses so the gate
+//! attribution (`why_rejected`) has a work list.
+use sylpheed_formats::mesh::{debug_resource_params, xbg7_resource_names, Xbg7Model};
+use std::collections::HashSet;
+
+fn main() {
+    let dir = std::env::args().nth(1).expect("resource3d dir");
+    let show = std::env::args().nth(2).is_some();
+    let mut files: Vec<_> = std::fs::read_dir(&dir)
+        .unwrap()
+        .flatten()
+        .map(|e| e.path())
+        .filter(|p| p.extension().and_then(|s| s.to_str()) == Some("xpr"))
+        .collect();
+    files.sort();
+
+    let (mut total, mut decoded, mut no_decl) = (0usize, 0usize, 0usize);
+    let mut misses: Vec<String> = Vec::new();
+    for f in &files {
+        let Ok(bytes) = std::fs::read(f) else { continue };
+        let names = xbg7_resource_names(&bytes);
+        if names.is_empty() {
+            continue;
+        }
+        let got: HashSet<String> = Xbg7Model::anchor_models_cancellable(&bytes, 0.0, &|| false)
+            .into_iter()
+            .map(|m| m.name)
+            .collect();
+        for n in &names {
+            total += 1;
+            if got.contains(n) {
+                decoded += 1;
+            } else if debug_resource_params(&bytes, n).is_none() {
+                // No vertex declaration / no index markers: the anchor scan
+                // never even considers these, so they are a different question
+                // from "searched and not found".
+                no_decl += 1;
+            } else {
+                misses.push(format!("{}|{n}", f.file_name().unwrap().to_string_lossy()));
+            }
+        }
+    }
+    println!(
+        "XBG7 resources: {total} total, {decoded} decoded ({:.1}%), {no_decl} without a usable descriptor, {} searched-and-missed",
+        100.0 * decoded as f64 / total as f64,
+        misses.len()
+    );
+    if show {
+        for m in &misses {
+            println!("{m}");
+        }
+    }
+}