re(xbg7): characterise the residual 47 misses — 99.25% of resources decode

examples/why_missed.rs reports the furthest gate per undecoded resource. Disc-wide
that is 47 rows / 43 distinct names, and they are mostly not ship geometry:

  30  e_rou_/_rou_ pose & proxy composites (24-vertex marker boxes, extent 0.010)
   6  .DAT particle composites in ptc_pack
   8  damage/LOD variants (e101_bdy_02_d, e901_wing_05_*_m, ...)
   3  props/other (g005 extent 0.196, _rou_f001_wep_05, e_rou_e005)

By gate: extent 32, coverage 8, winding 7. The extent bucket is almost entirely the
pose-proxy boxes, and lowering that floor was measured and refuted earlier. The one
genuinely interesting residual is e901_wing_05_L/R at winding 0.587/0.570 against the
0.70 floor — the signature of a thin double-sided sheet, unproven without a capture
with the boss on screen (flying stage 16 puts the container in memory but the unit
never appeared).

So: 6 247 / 6 294 resources decode (99.25 %), and every real mesh drawn in three
captured missions decodes at the GPU's own offsets with index runs matching byte for
byte (93/93 and 128/128).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NptfmpjdpNCKEez6d2xvA9

crates/sylpheed-formats/examples/why_missed.rs

@@ -0,0 +1,19 @@
+//! Why does a named resource never decode? Reports the furthest gate its best
+//! candidate reached. Usage: why_missed <container.xpr> [name-substring]
+use sylpheed_formats::mesh::{debug_best_rejection, xbg7_resource_names, Xbg7Model};
+use std::collections::HashSet;
+fn main() {
+    let a: Vec<String> = std::env::args().collect();
+    let bytes = std::fs::read(&a[1]).unwrap();
+    let filter = a.get(2).cloned().unwrap_or_default();
+    let decoded: HashSet<String> = Xbg7Model::stage_models(&bytes).into_iter().map(|m| m.name).collect();
+    for n in xbg7_resource_names(&bytes) {
+        if decoded.contains(&n) || (!filter.is_empty() && !n.contains(&filter)) {
+            continue;
+        }
+        match debug_best_rejection(&bytes, &n) {
+            Some((rank, why)) => println!("{n:<28} rank {rank}  {why}"),
+            None => println!("{n:<28} (no candidate reached any gate / skipped before anchoring)"),
+        }
+    }
+}