fix: collisions keep the platform's order

Walking the systems sorted reordered the declarations doubled.py
reports from, so the export report named the CoCo reader first. The
declarations keep the platform's order again, and the packed file is
picked from the sorted walk the builder makes.

scripts/slots.py

@@ -675,7 +675,7 @@ class Collision:
 
     destination: str
     resolved: list[str]
-    # Each declaration with the file it resolved to, in the builder's order.
+    # Each declaration with the file it resolved to, in the platform's order.
     declarations: list[tuple[dict, str | None]] = field(default_factory=list)
     # The system of each declaration, in the same order.
     systems: list[str] = field(default_factory=list)
@@ -712,14 +712,14 @@ def find_collisions(
     """
     fold = bool(config.get("case_insensitive_fs", False))
     systems = config.get("systems") or {}
-    # The builder walks the systems sorted and lets a hash-constrained
-    # declaration that resolves by content take the path: the same order
-    # and the same choice say which file ships.
+    # The builder lets a hash-constrained declaration that resolves by
+    # content take the path, else the first it reaches walking the systems
+    # sorted: the same choice says which file ships.
     preferred = set(
         preferred_entries(systems, db, "bios", "", False, zip_contents, True).values()
     )
     by_dest: dict[str, list[tuple[str, dict]]] = {}
-    for sys_id, system in sorted(systems.items()):
+    for sys_id, system in systems.items():
         for entry in system.get("files") or []:
             if not isinstance(entry, dict):
                 continue
@@ -751,9 +751,13 @@ def find_collisions(
             # also names the first one's file.
             if any(_accepted_by_all(path, entries, db) for path in resolved):
                 continue
+            reached = sorted(
+                (sys_id, local)
+                for (sys_id, _entry), (_e, local) in zip(claims, declarations) if local
+            )
             shipped = next(
                 (local for entry, local in declarations if local and id(entry) in preferred),
-                resolved[0],
+                reached[0][1],
             )
             collisions.append(
                 Collision(