gwshop: fix primary-branch tie-break and refresh the committed catalog

- src/gwshop.rs: pick the FIRST longest facet path on ties, matching the
  original Python max(paths, key=len). Rust's max_by_key returned the last,
  which silently reclassified ~2298 entries for products faceted under
  several branches (e.g. a generic kit listed per chapter). Adds a regression
  test.
- AGENTS.md: document the first-longest tie-break and the facet-partition
  coverage shortfall (non-system merchandise left out; no model kits).
- data/gwshop_catalog.json: regenerate with the fixed binary (3491 -> 3459
  entries; 34 removed, 2 added, 188 structural + 785 collections changes).

AGENTS.md

@@ -242,6 +242,14 @@ sorting pipeline — **change it first, then the code**. Summary:
   public **search-only** key live in the gitignored `algolia.json` (or
   `ALGOLIA_APP_ID`/`ALGOLIA_API_KEY`); never commit any other Algolia key.
   `data/gwshop_catalog.json` is the committed snapshot and the sorter default.
+- The dump partitions the index on the `GameSystemsRoot` hierarchical facet
+  (the search-only key cannot `/browse`; plain pagination caps at 1000 hits).
+  When a product is faceted under several branches of equal depth (e.g. a
+  generic kit listed per chapter), the **first longest path wins** — Python's
+  `max(paths, key=len)` semantics, reproduced explicitly because Rust's
+  `max_by_key` returns the *last* maximum. Products carrying no
+  `GameSystemsRoot` path (paints, Black Library books, White Dwarf, bases,
+  gifts — no miniature kits) are left out; the coverage shortfall is logged.
 - Bookkeeping (`sorter_applied.jsonl`, `sorter_low_confidence.txt`) is written
   to `<library>/../_logs/` by default — never inside the library, which may be
   a seeded torrent whose file set is frozen.

src/gwshop.rs

@@ -454,12 +454,18 @@ pub fn build_catalog(hits: &[Value]) -> Value {
             continue;
         }
         // primary branch = longest path (most specific), e.g.
-        // [40k, Space Marines, Raven Guard, Walker]
-        let primary = paths
-            .iter()
-            .max_by_key(|p| p.len())
-            .cloned()
-            .unwrap_or_default();
+        // [40k, Space Marines, Raven Guard, Walker].
+        // python `max(paths, key=len)` keeps the FIRST longest path on ties;
+        // Rust's `max_by_key` would keep the LAST, so select explicitly to
+        // stay faithful to the original (products faceted under several
+        // branches, e.g. a generic kit listed per chapter, depend on this).
+        let primary = paths.iter().fold(Vec::new(), |best, p| {
+            if p.len() > best.len() {
+                p.clone()
+            } else {
+                best
+            }
+        });
         let at = |i: usize| -> Value {
             primary
                 .get(i)
@@ -596,6 +602,30 @@ mod tests {
         assert_eq!(e["source"], "gwshop");
     }
 
+    #[test]
+    fn build_catalog_primary_branch_prefers_first_longest_tie() {
+        // python max(paths, key=len) keeps the first longest path; the class
+        // layer must come from that branch, not the last tied one.
+        let hit = json!({
+            "objectID": "obj3",
+            "name": "Stomper Tribe",
+            "sku": "S3",
+            "GameSystemsRoot": {
+                "lvl0": ["Age of Sigmar"],
+                "lvl1": ["Age of Sigmar > Grand Alliance Destruction"],
+                "lvl2": ["Age of Sigmar > Grand Alliance Destruction > Sons of Behemat"],
+                "lvl3": [
+                    "Age of Sigmar > Grand Alliance Destruction > Sons of Behemat > Gargant",
+                    "Age of Sigmar > Grand Alliance Destruction > Sons of Behemat > Monster",
+                ],
+            }
+        });
+        let cat = build_catalog(&[hit]);
+        let e = &cat["entries"][0];
+        assert_eq!(e["faction"], "Sons of Behemat");
+        assert_eq!(e["class"], "Gargant");
+    }
+
     #[test]
     fn build_catalog_dedups_and_handles_pathless() {
         let hit = json!({"objectID": "obj2", "name": "Paint"});