refactor: make sku_list resolve provider aliases generically

- Replace Together-specific import logic with generic provider prefix stripping
- Addresses PR #2796 review feedback about provider-specific code in core modules
- Add comprehensive test suite covering normal cases, provider prefixes, and edge cases
- Maintains backward compatibility while keeping sku_list provider-agnostic

llama_stack/models/llama/sku_list.py

@@ -19,9 +19,42 @@ LLAMA3_VOCAB_SIZE = 128256
 
 
 def resolve_model(descriptor: str) -> Model | None:
+    """Return the canonical `Model` that matches *descriptor*.
+
+    The helper originally accepted the model *descriptor* (e.g. "Llama-4-Scout-17B-16E-Instruct")
+    or the HuggingFace repository path (e.g. "meta-llama/Llama-4-Scout-17B-16E-Instruct").
+
+    Review feedback (see PR #2796) highlighted that callers - especially provider
+    adaptors - were passing provider-qualified aliases such as
+
+        "together/meta-llama/Llama-4-Scout-17B-16E-Instruct"
+
+    Having provider-specific logic here is undesirable.  Instead of hard-coding
+    aliases in *this* file we normalise the incoming descriptor by stripping a
+    leading provider prefix of the form "<provider>/" (e.g. "together/",
+    "groq/", …) *once* and then retry the lookup.  This keeps sku_list
+    provider-agnostic while still resolving all legitimate aliases that
+    individual providers register in their own modules.
+    """
+
+    # Direct match against descriptor or HF repo.
     for m in all_registered_models():
         if descriptor in (m.descriptor(), m.huggingface_repo):
             return m
+
+    # Handle provider-prefixed aliases - strip provider prefix ("together/", "groq/", etc.) if present.
+    if "/" in descriptor:
+        # Many provider aliases look like "<provider>/<repo_path>"; we only need
+        # the repo_path (everything after the first slash) for a successful
+        # lookup.  Splitting just once avoids over-stripping repo paths that
+        # legitimately contain more than one component (e.g. "meta-llama/…").
+        _, remainder = descriptor.split("/", 1)
+        # Recursively attempt to resolve the stripped descriptor to avoid code
+        # duplication.  The depth here is at most 1 because the second call will
+        # hit the fast path above.
+        if remainder != descriptor:  # guard against infinite recursion
+            return resolve_model(remainder)
+
     return None