fix(assets): treat explicit empty hash filter as exact-match miss

Address review findings on the listAssets contract PR:

- Empty `?hash=` no longer collapses to "no filter" (which returned a full
  unfiltered page); it now stays "" and is matched exactly, yielding an
  empty page — consistent with the documented "malformed -> empty page"
  contract. Omitting the param entirely still disables the filter.
- Guard `list_references_page` on `asset_hash is not None` (page + count)
  so the present-empty vs omitted distinction is preserved.
- Add tests for hash normalization (uppercase/whitespace) and for the
  explicit-empty -> empty-page behavior.
- Clarify the `include_public` comment: core reads are owner-scoped with no
  separate public pool, so the flag is inert here; cloud enforces it in its
  own service layer.

app/assets/api/schemas_in.py

@@ -59,9 +59,11 @@ class ListAssetsQuery(BaseModel):
     # is `asset_hash`; the query param is `hash`).
     hash: str | None = None
 
-    # Declared for cloud/core contract parity. Core has no public asset pool, so
-    # this is inert: results are always the caller's own assets. Accepted (not
-    # rejected) so the FE needs no isCloud branch.
+    # Declared for cloud/core contract parity. In core, reads are owner-scoped
+    # (owner_id == "") and there is no separate shared/public pool for this flag
+    # to include or exclude, so it is inert here and intentionally not threaded
+    # into the query. Accepted (not rejected) so the FE needs no isCloud branch;
+    # cloud enforces the flag in its own service layer.
     include_public: bool = True
 
     # Accept either a JSON string (query param) or a dict
@@ -102,9 +104,11 @@ class ListAssetsQuery(BaseModel):
         # Normalize for an exact match against stored hashes (which are
         # lowercase `blake3:<hex>`). Liberal in what we accept — no pattern
         # enforcement; a non-matching value simply yields an empty page.
+        # An explicitly-supplied-but-empty value (`?hash=`) stays `""` so it
+        # is treated as an exact-match miss (empty page), not silently dropped
+        # to "no filter" — omit the param entirely to disable the filter.
         if isinstance(v, str):
-            v = v.strip().lower()
-            return v or None
+            return v.strip().lower()
         return v
 
     @field_validator("metadata_filter", mode="before")

app/assets/database/queries/asset_reference.py

@@ -294,7 +294,9 @@ def list_references_page(
         escaped, esc = escape_sql_like_string(name_contains)
         base = base.where(AssetReference.name.ilike(f"%{escaped}%", escape=esc))
 
-    if asset_hash:
+    # `is not None` (not truthiness): an explicit empty hash is an exact-match
+    # miss (empty page), while an omitted hash (None) disables the filter.
+    if asset_hash is not None:
         base = base.where(Asset.hash == asset_hash)
 
     base = apply_tag_filters(base, include_tags, exclude_tags)
@@ -349,7 +351,7 @@ def list_references_page(
         count_stmt = count_stmt.where(
             AssetReference.name.ilike(f"%{escaped}%", escape=esc)
         )
-    if asset_hash:
+    if asset_hash is not None:
         count_stmt = count_stmt.where(Asset.hash == asset_hash)
     count_stmt = apply_tag_filters(count_stmt, include_tags, exclude_tags)
     count_stmt = apply_metadata_filter(count_stmt, metadata_filter)

tests-unit/assets_test/test_list_filter.py

@@ -366,6 +366,51 @@ def test_list_assets_hash_filter_no_match(http, api_base, asset_factory, make_as
     assert body["total"] == 0
 
 
+def test_list_assets_hash_filter_normalizes_case_and_whitespace(
+    http, api_base, asset_factory, make_asset_bytes
+):
+    """`hash` is trimmed and lowercased before matching, so an upper-cased,
+    space-padded value still matches the stored lowercase hash."""
+    scope = f"lf-hashnorm-{uuid.uuid4().hex[:6]}"
+    tags = ["models", "checkpoints", "unit-tests", scope]
+    a = asset_factory("hnorm_a.safetensors", tags, {}, make_asset_bytes("hnorm_a", 1024))
+
+    target = a["hash"]
+    assert target == target.lower(), "stored hash is expected to be lowercase"
+    messy = f"  {target.upper()}  "
+
+    r = http.get(
+        api_base + "/api/assets",
+        params={"hash": messy, "limit": "50"},
+        timeout=120,
+    )
+    body = r.json()
+    assert r.status_code == 200, body
+    names = [x["name"] for x in body["assets"]]
+    assert names == [a["name"]]
+    assert body["total"] == 1
+
+
+def test_list_assets_hash_filter_empty_returns_empty_page(
+    http, api_base, asset_factory, make_asset_bytes
+):
+    """An explicitly-supplied but empty `hash` (`?hash=`) is an exact-match miss
+    and returns an empty page, rather than silently disabling the filter."""
+    scope = f"lf-hashempty-{uuid.uuid4().hex[:6]}"
+    tags = ["models", "checkpoints", "unit-tests", scope]
+    asset_factory("he_a.safetensors", tags, {}, make_asset_bytes("he_a", 800))
+
+    r = http.get(
+        api_base + "/api/assets",
+        params={"hash": "", "limit": "50"},
+        timeout=120,
+    )
+    body = r.json()
+    assert r.status_code == 200, body
+    assert body["assets"] == []
+    assert body["total"] == 0
+
+
 def test_list_assets_include_public_accepted(http, api_base, asset_factory, make_asset_bytes):
     """`include_public` is accepted for contract parity; core results are always
     the caller's own assets regardless of its value (the param is inert)."""