refactor: extract multipart upload parsing from routes

- Add app/assets/api/upload.py with parse_multipart_upload() for HTTP parsing
- Add ParsedUpload dataclass to schemas_in.py
- Add domain exceptions (AssetValidationError, AssetNotFoundError, HashMismatchError)
- Add manager.process_upload() with domain exceptions (no HTTP status codes)
- Routes map domain exceptions to HTTP responses
- Slim down upload_asset route to ~20 lines (was ~150)

Amp-Thread-ID: https://ampcode.com/threads/T-019c2519-abe1-738a-ad2e-29ece17c0e42
Co-authored-by: Amp <amp@ampcode.com>

app/assets/manager.py

@@ -12,9 +12,19 @@ import mimetypes
 import contextlib
 from typing import Sequence
 
+from pydantic import ValidationError
+
+import folder_paths
 import app.assets.services.hashing as hashing
 from app.database.db import create_session
 from app.assets.api import schemas_out, schemas_in
+from app.assets.api.schemas_in import (
+    AssetNotFoundError,
+    AssetValidationError,
+    HashMismatchError,
+    ParsedUpload,
+)
+from app.assets.api.upload import _cleanup_temp
 from app.assets.database.queries import (
     asset_exists_by_hash,
     fetch_asset_info_and_asset,
@@ -292,6 +302,81 @@ def upload_asset_from_temp_path(
     )
 
 
+def process_upload(
+    parsed: ParsedUpload,
+    owner_id: str = "",
+) -> schemas_out.AssetCreated:
+    """
+    Process a parsed multipart upload.
+
+    Args:
+        parsed: The parsed upload data from parse_multipart_upload
+        owner_id: The owner ID for the asset
+
+    Returns:
+        AssetCreated response (check created_new to determine if new asset was created)
+
+    Raises:
+        UploadError: On validation or processing errors
+    """
+    try:
+        spec = schemas_in.UploadAssetSpec.model_validate({
+            "tags": parsed.tags_raw,
+            "name": parsed.provided_name,
+            "user_metadata": parsed.user_metadata_raw,
+            "hash": parsed.provided_hash,
+        })
+    except ValidationError as ve:
+        _cleanup_temp(parsed.tmp_path)
+        raise AssetValidationError("INVALID_BODY", f"Validation failed: {ve.json()}")
+
+    # Validate models category against configured folders
+    if spec.tags and spec.tags[0] == "models":
+        if len(spec.tags) < 2 or spec.tags[1] not in folder_paths.folder_names_and_paths:
+            _cleanup_temp(parsed.tmp_path)
+            category = spec.tags[1] if len(spec.tags) >= 2 else ""
+            raise AssetValidationError("INVALID_BODY", f"unknown models category '{category}'")
+
+    # Fast path: if a valid provided hash exists, create AssetInfo without writing anything
+    if spec.hash and parsed.provided_hash_exists is True:
+        result = create_asset_from_hash(
+            hash_str=spec.hash,
+            name=spec.name or (spec.hash.split(":", 1)[1]),
+            tags=spec.tags,
+            user_metadata=spec.user_metadata or {},
+            owner_id=owner_id,
+        )
+
+        if result is None:
+            raise AssetNotFoundError(f"Asset content {spec.hash} does not exist")
+
+        # Drain temp if we accidentally saved (e.g., hash field came after file)
+        _cleanup_temp(parsed.tmp_path)
+        return result
+
+    # Otherwise, we must have a temp file path to ingest
+    if not parsed.tmp_path or not os.path.exists(parsed.tmp_path):
+        raise AssetNotFoundError("Provided hash not found and no file uploaded.")
+
+    try:
+        return upload_asset_from_temp_path(
+            spec,
+            temp_path=parsed.tmp_path,
+            client_filename=parsed.file_client_name,
+            owner_id=owner_id,
+            expected_asset_hash=spec.hash,
+        )
+    except ValueError as e:
+        _cleanup_temp(parsed.tmp_path)
+        msg = str(e)
+        if "HASH_MISMATCH" in msg or msg.strip().upper() == "HASH_MISMATCH":
+            raise HashMismatchError("Uploaded file hash does not match provided hash.")
+        raise AssetValidationError("BAD_REQUEST", "Invalid inputs.")
+    except Exception:
+        _cleanup_temp(parsed.tmp_path)
+        raise
+
+
 def update_asset(
     asset_info_id: str,
     name: str | None = None,
@@ -332,7 +417,7 @@ def set_asset_preview(
         owner_id=owner_id,
     )
     info = result["info"]
-    asset = result["asset"]
+    asset = result["asset"]T
     tags = result["tags"]
 
     return schemas_out.AssetDetail(