feat(backend): CivitAI download support for other model types with subtype routing

py/services/download_routing.py

@@ -10,9 +10,13 @@ two can never disagree.
 from __future__ import annotations
 
 import logging
-from typing import Iterable
+from typing import Iterable, Optional
 
-from ..utils.constants import DIFFUSION_MODEL_BASE_MODELS
+from ..utils.constants import (
+    CIVITAI_FILE_TYPE_TO_OTHER_SUB_TYPE,
+    CIVITAI_TYPE_TO_OTHER_SUB_TYPE,
+    DIFFUSION_MODEL_BASE_MODELS,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -51,3 +55,49 @@ def is_diffusion_model_download(
         return True
 
     return False
+
+
+def resolve_other_download_sub_type(
+    civitai_model_type: str,
+    file_types: Iterable[str] = (),
+    selected_file_type: Optional[str] = None,
+) -> Optional[str]:
+    """Resolve the "other"-page sub_type for a download.
+
+    Fixed priority (locked design, docs/plans/other-models-page.md §9.2):
+
+    1. Explicit user file pick — when the picked file's type maps, it wins
+       even when model.type maps to something else.
+    2. model.type via CIVITAI_TYPE_TO_OTHER_SUB_TYPE.
+    3. file.type fallback — only when model.type maps to nothing. Must NOT
+       override a mapped model.type: checkpoint models routinely bundle
+       VAE/Text Encoder component files.
+    4. Still undecidable -> None (caller must ask the user for a folder).
+    """
+    if selected_file_type:
+        mapped = CIVITAI_FILE_TYPE_TO_OTHER_SUB_TYPE.get(selected_file_type)
+        if mapped:
+            logger.info(
+                "Explicit file pick type '%s' routes other download to '%s'",
+                selected_file_type,
+                mapped,
+            )
+            return mapped
+
+    normalized_model_type = (civitai_model_type or "").strip().lower()
+    mapped = CIVITAI_TYPE_TO_OTHER_SUB_TYPE.get(normalized_model_type)
+    if mapped:
+        return mapped
+
+    for file_type in file_types:
+        mapped = CIVITAI_FILE_TYPE_TO_OTHER_SUB_TYPE.get(file_type)
+        if mapped:
+            logger.info(
+                "model.type '%s' unmapped; file type '%s' routes other download to '%s'",
+                civitai_model_type,
+                file_type,
+                mapped,
+            )
+            return mapped
+
+    return None