refactor: split the cross-reference into its two views

generate_cross_reference rendered the same relation twice in one
function, once per platform and once per upstream, and reached
complexity 53. Each view is now its own function and the caller is a
pair of calls.

Verified by generating the site with both versions against the same
data: all 533 pages identical apart from timestamps, with a control run
of the same code twice to confirm the comparison had no drift in it.

scripts/generate_site.py

@@ -3174,44 +3174,11 @@ def generate_gap_analysis(
 
 
 
-def generate_cross_reference(
-    coverages: dict,
-    profiles: dict,
-) -> str:
-    """Generate cross-reference: Platform -> Core -> Systems -> Upstream."""
-    unique = {
-        k: v for k, v in profiles.items() if v.get("type") not in ("alias", "test")
-    }
-
-    # Build core -> profile lookup by core name
-    core_to_profile: dict[str, str] = {}
-    for pname, p in unique.items():
-        for core in p.get("cores", [pname]):
-            core_to_profile[str(core)] = pname
-
-    total_cores = len(unique)
-    total_upstreams = len({
-        p.get("upstream", p.get("source", ""))
-        for p in unique.values()
-        if p.get("upstream") or p.get("source")
-    })
-
-    lines = [
-        f"# Cross-reference - {SITE_NAME}",
-        "",
-        f"Platform > Core > Systems > Upstream emulator. "
-        f"{total_cores} cores across {len(coverages)} platforms, "
-        f"tracing back to {total_upstreams} upstream projects.",
-        "",
-        "The libretro core is a port of the upstream emulator. "
-        "Files, features, and validation may differ between the two.",
-        "",
-        "[Download cross-reference CSV](downloads/cross-reference.csv){ .md-button } "
-        "[Open emulator API](api/v1/emulators.json){ .md-button } "
-        "[All data exports](data.md){ .md-button }",
-        "",
-    ]
-
+def _render_xref_by_platform(
+    coverages: dict, unique: dict, core_to_profile: dict
+) -> list[str]:
+    """Which cores each platform pulls in, and what they need."""
+    lines: list[str] = []
     # Per platform
     for pname in sorted(coverages.keys(), key=lambda x: coverages[x]["platform"]):
         cov = coverages[pname]
@@ -3306,6 +3273,14 @@ def generate_cross_reference(
 
         lines.append("")
 
+    return lines
+
+
+def _render_xref_by_upstream(
+    coverages: dict, unique: dict, core_to_profile: dict
+) -> list[str]:
+    """The same relation read the other way: one row per upstream."""
+    lines: list[str] = []
     # Reverse view: by upstream emulator
     lines.extend(
         [
@@ -3365,6 +3340,50 @@ def generate_cross_reference(
             f"{cls_str} | {plat_str} |"
         )
 
+    return lines
+
+
+def generate_cross_reference(
+    coverages: dict,
+    profiles: dict,
+) -> str:
+    """Generate cross-reference: Platform -> Core -> Systems -> Upstream."""
+    unique = {
+        k: v for k, v in profiles.items() if v.get("type") not in ("alias", "test")
+    }
+
+    # Build core -> profile lookup by core name
+    core_to_profile: dict[str, str] = {}
+    for pname, p in unique.items():
+        for core in p.get("cores", [pname]):
+            core_to_profile[str(core)] = pname
+
+    total_cores = len(unique)
+    total_upstreams = len({
+        p.get("upstream", p.get("source", ""))
+        for p in unique.values()
+        if p.get("upstream") or p.get("source")
+    })
+
+    lines = [
+        f"# Cross-reference - {SITE_NAME}",
+        "",
+        f"Platform > Core > Systems > Upstream emulator. "
+        f"{total_cores} cores across {len(coverages)} platforms, "
+        f"tracing back to {total_upstreams} upstream projects.",
+        "",
+        "The libretro core is a port of the upstream emulator. "
+        "Files, features, and validation may differ between the two.",
+        "",
+        "[Download cross-reference CSV](downloads/cross-reference.csv){ .md-button } "
+        "[Open emulator API](api/v1/emulators.json){ .md-button } "
+        "[All data exports](data.md){ .md-button }",
+        "",
+    ]
+
+    lines.extend(_render_xref_by_platform(coverages, unique, core_to_profile))
+    lines.extend(_render_xref_by_upstream(coverages, unique, core_to_profile))
+
     lines.extend(["", f"*Generated on {_timestamp()}*"])
     return "\n".join(lines) + "\n"